RU2303323C1 - Method and device for directional phase-failure ground-fault protection of ac distribution network - Google Patents

Abstract

FIELD: selective phase-failure ground-fault protection of power networks with arbitrarily connected neutral.

SUBSTANCE: proposed method involves detection of too high first half-wave amplitudes in high-frequency components of zero-sequence current and voltage exceeding reference value. Phase shift between them is measured as soon as high-frequency current crosses zero, Phase shift equal to or about 90 deg. is recorded during check interval. Then low and maximal admissible amplitudes of zero-sequence voltage low-frequency component is checked. Assumed as maximal admissible amplitude of low-frequency component is maximal short-time shift of neutral admissible for particular line. Assumed as low-value of low-frequency component amplitude is continuous maximal level of neutral shift admissible for particular line. Low-frequency component amplitude is checked for excess above low value under check. If result is adequate, low-frequency component amplitude is measured during check interval. Alarm signal is generated upon recording of excess value in time interval specified including time period of high-frequency transients on occurrence of phase-failure ground faults, time taken to compensate for capacitive currents on occurrence of phase-failure ground faults, and time required to tune away noise and self-eliminated phase-failure ground faults. Device implementing proposed method has high-frequency current and voltage channels and low-frequency zero-sequence voltage channel, phase-sensing element, control circuit, four delay shapers, phase detection result clear unit, and alarm signal generating circuit.

EFFECT: enhanced reliability and selectivity, reduced malfunction probability.

6 cl, 4 dwg

Description

 The invention relates to the protection of electrical lines from accidents, namely to protection that responds to earth fault current, and can be used for selective protection in case of a single-phase earth fault in distribution electric networks with any neutral connection method.

A patent search in relation to the claimed method of directional protection against a single-phase earth fault in an alternating current distribution electric network showed the following.

A known method of directional protection against a single-phase earth fault in an alternating current electrical distribution network, which is implemented in a device for directional protection of a zero sequence from a single-phase earth fault in a network with insulated neutral (USSR, copyright certificate No. 792421, Н02Н 3/16, 1980) . In accordance with the method, the phase difference between the current and voltage signals of the zero sequence is measured at the operating frequency of the network, the results of measurements are compared with the specified interval of phase angle angles, the signal of the high-frequency component of the zero sequence current is isolated, and its amplitude is compared with the reference value, while the reference is exceeded the values of the amplitude of the high-frequency component of the zero sequence current and finding the phase shift in a given interval form a ariyny signal.

The disadvantage of this method is that in it to detect a single-phase earth fault (SCR), the low-frequency components of the current and voltage of the zero sequence are analyzed, namely, the phase shift between the low-frequency components of the current and voltage of the zero sequence is monitored. This does not reflect the reliable state of the line during a single-phase earth fault, since during the single-phase earth fault (OZZ), the high-frequency transient that occurs in this case plays a significant role. The presence in the method of the operation of isolating the signal of the high-frequency component of the current of the zero sequence and the control of its exceeding the amplitude of the reference value does not guarantee that the detected excess is caused by the interference signal, since the method does not identify the selected high-frequency component. As a result , the reliability of the method decreases, the selectivity with respect to the interference signal decreases, and the likelihood of false positives increases. In addition, in the method there is no control of the amplitude of the voltage of the zero sequence during the SCR, which reduces the reliability of the method, and therefore, increases the likelihood of false positives.

Closest to the proposed one is a method of directional protection against a single-phase earth fault in a distribution electric AC network (RF Patent No. 2097893, Н02Н 3/16, 11.27.97). SUBSTANCE: method involves isolating a low-frequency component corresponding to the operating frequency from a zero-sequence voltage signal from a zero voltage signal, extracting high-frequency components from current and zero-sequence voltage signals, measuring the amplitudes of their first half-waves, comparing the measurement results with the corresponding reference values and, if there is a simultaneous excess over the reference values , fixing the phase relationship between the signals of the high-frequency components of the current and voltage zero At the moment when the high-frequency current passes through zero, the amplitude of the extracted low-frequency signal of the zero sequence voltage is simultaneously measured, the obtained value is compared with the reference one, the result is recorded, then the results are compared and, when the phase angle is found in the specified interval and if the maximum value is exceeded by the voltage amplitude zero sequence, control the preservation of the obtained measurement results for a given time interval, while maintaining enii measurement results after a predetermined time interval is formed alarm, the duration of the predetermined time interval is set according to length of time of existence of high frequency transients at single-phase fault to ground or to increase it to the time interval required for compensation of capacitive currents in single-phase earth fault.

The disadvantage of this method consists, first of all, in the reduction of selectivity to the interference signal due to the lack of the ability to ensure, when determining the SCR, a clear reference of the fixed phase relationship between the signals of the high-frequency components of the current and voltage of the zero sequence at the time the high-frequency current passes through zero to the measured amplitude of the low-frequency component zero sequence voltage. This is due to the fact that the process of detecting signs of SCR at high and low frequencies proceeds independently, without reference to each other in time: phase shift is fixed, the amplitude of the low-frequency component of the zero-sequence voltage is fixed, compared with reference values, when the angle is within the specified limits and the presence exceeding the amplitude of the maximum allowable value at a given time interval forms a signal about the presence of the SCR. In this case, both the result of monitoring the phase shift and the result of monitoring the excess of the amplitude of the low-frequency component of the zero-sequence voltage can be the result of an interference signal. The inability to control the simultaneous occurrence of both signs of the SCR can lead to a false response of the device by an interference signal, the source of which, as already mentioned, in this case can be both low-frequency and high-frequency channels.

In addition, the method provides only one reference value of the amplitude of the LF component of the voltage of the zero sequence, while in accordance with the Rules for the technical operation of power plants and networks of the Russian Federation (PTE) during the operation of the network, the neutral voltage is zero only when the phase conductivity is completely symmetrical relative to the earth. In normal mode, the natural asymmetry is due to the different arrangement of wires on the supports, the uneven distribution of capacitors in phases to protect rotating machines, coupling capacitors and other work of technological equipment. In addition, the consumer himself introduces an artificial neutral bias in some situations to ensure the network is operational. In the presence of asymmetry, a neutral bias occurs. As a result, distribution electric networks have such parameters as the maximum short-term neutral displacement level acceptable for a given network (up to two hours) and the long-term maximum neutral displacement level that is less than half the permissible short-term maximum level (Rules for the technical operation of electric stations and networks of the Russian Federation Federation / Ministry of Fuel and Energy of the Russian Federation, RAO "UES of Russia", M .: SPO OGRES, 1996, pp. 280-287, hereinafter PTE). Thus, with neutral offsets, it is allowed for a limited time that the voltage amplitude exceeds the zero sequence value corresponding to the operating mode of the network. Moreover, as follows from the PTE, these maximum values for the distribution network are known. In the known method there are no means to control two voltage levels of the low-frequency signal. This does not allow to take into account the possibility of a neutral bias permissible by PTE, and therefore does not allow to exclude an unjustified disconnection of the network connection, i.e. reduces the reliability of the method and increases the likelihood of a false positive protection.

The permissible long-term maximum level of neutral bias is less than half the permissible short-term maximum level. However, in distribution electric networks with a neutral bias, in which a voltage is established on the neutral that corresponds to the permissible long-term maximum level of the neutral bias, the fixation of the excess of the lower level can also be a sign of an SCR or an interference signal. The lack of the method of controlling the time variation of the permissible long-term maximum level of neutral bias reduces the reliability of protection against the SCR, and therefore reduces the reliability of the method. In addition, with SCR at the beginning and at the end of the development of neutral voltage (at the beginning and at the end of the transient envelope), interference noise can be generated. The lack of the ability to track, during OZZ, changes in the amplitude of the low-frequency signal, starting from the lower level, taking into account the presence of noise, it does not allow to tune out interference noise at the beginning and at the end of the envelope, which reduces the reliability and selectivity of the method with respect to the interference signal, which increases the likelihood of false positives. The inability to control the excess of the amplitude of the low frequency component of the zero sequence voltage using two threshold amplitude values does not allow to cover all possible causes of the neutral bias, as well as the individuality of the electrical parameters of the network, which deprives the known method of universality.

In addition, in the known method, when deciding on the issuance of a signal for the presence of OZZ, the possibility of the influence of interference signals is not taken into account. As a result, the selectivity with respect to the interference signal is reduced, and therefore, the likelihood of false alarms is increased.

Thus, the analogue and prototype of the claimed method of directional protection against a single-phase earth fault in an electric AC network, identified as a result of a patent search, do not allow achieving a technical result when increasing the reliability of the method, increasing the selectivity with respect to the interference signal and reducing the likelihood of false positives.

The results of a patent search conducted in relation to a device for implementing the inventive method showed the following.

A device for directional protection of the zero sequence from a single-phase earth fault in a network with isolated neutral, containing channels of current and voltage of the zero sequence and the high-frequency component of the current of the zero sequence. The outputs of the channels of current and zero sequence voltage are connected to a phase-sensitive element, which is connected through a threshold element to one of the inputs of the output signal generating circuit, the second input of which is connected to the channel output of the high-frequency component of the zero sequence current, and the circuit output is the output of the device. In addition, the channel of the high-frequency component of the zero-sequence current contains a series-connected high-pass filter, the input of which is the input of the channel, and a threshold element, the output of which is the output of the channel (USSR, copyright certificate No. 792421, H2N 3/16, 1980). The device generates an alarm when the phase angle of the current and voltage of the zero sequence are found in the specified interval at the operating frequency of the network and if there is a zero sequence of harmonics of the working frequency with an amplitude exceeding the permissible in the high-frequency component of the current.

A disadvantage of the known device for protecting against a single-phase earth fault in an alternating current electric network is its low noise immunity during the transition mode of restoration of symmetry of the phase voltages of the network after eliminating a single-phase earth fault and, as a consequence, in increasing the probability of false alarms. This is because with a single-phase earth fault, the frequency of freely damped oscillations is determined by the equivalent inductance of the measuring transformers of zero voltage sequence and the total capacitance relative to the ground. The non-linearity of the inductance of voltage transformers contributes to the formation of high-frequency components in the current and voltage of the zero sequence. At the same time, some of them appear in the response band of the zero sequence channel, which leads to a false response of the protection.

The need for reliable isolation of low-frequency voltage and zero-sequence current signals, that is, detuning from high-frequency signals (HFS) of voltage and zero-sequence current when a threshold element is triggered, having a much larger amplitude than the steady-state current of a single-phase earth fault at the operating frequency, causes other problems . Typically, the filtering ability of low-pass filters (low-pass filters) is improved to this end. However, stricter filtering increases the inertia of the low-pass filter, which can lead to a false response of the phase-sensitive element, i.e. cause the device to malfunction. In addition, it is known that the establishment of transients in the low-pass filter or the time of the correct response of the threshold element (PE) to the signal from the low-pass filter can last T _f = (3-5) ω ^-1 , where ω is the operating frequency. In the arc OZZ mode, the shock effects of the HF voltage and zero-sequence current of large amplitude excite the natural oscillations of the low-pass filter. The addition of the natural oscillations of the low-pass filter from the next breakdowns of the OZZ depending on the interval of their repetition can lead to both PE triggering and failure. In the event of a PE triggering, a significant additional phase shift will occur at the output of the coupled input blocks of the low-pass filter + PE due to pulse-width modulation by the total PE signal. It can also lead to a false response of a phase-sensitive element that analyzes the PE outputs, which leads to a false response of the device.

Since the known device for detecting the SCR allows you to analyze only the low-frequency components (LF) of the current and voltage of the zero sequence, namely, it controls the phase shift between the low-frequency components, this does not reflect the reliable state of the network connection during a single-phase earth fault, since during the SCR plays a significant role the resulting high-frequency transient. The ability of the device to control the signal of the high-frequency component of the zero sequence current and to exceed its amplitude with the reference value does not guarantee that the detected excess is not caused by an interference signal, since the device does not have the ability to identify the selected high-frequency component. As a result, the reliability of monitoring the presence of an OZZ decreases, and therefore, the reliability of the device decreases, the selectivity with respect to the interference signal decreases, and the likelihood of false alarms increases. The channel of the high-frequency component of the zero-sequence current only monitors the presence of the maximum permissible level of high-frequency harmonics in the signal of the zero-sequence current at the industrial frequency. At the same time, the device does not have the means to make sure that exceeding the threshold value is not caused by an interference signal. In addition, the device does not have the ability to control the amplitude of the NPP voltage of the zero sequence during the SCR, which also reduces the reliability of the control results, since the presence of an excess of the amplitude of the PSP voltage of the zero sequence in this case is one of the reliable signs of the SCR. As a result, the reliability of the device decreases and the likelihood of false positives increases.

Closest to the proposed one is a device for directional protection against a single-phase earth fault in an electrical alternating current network (RF Patent No. 2097893, Н02Н 3/16, 11.27.97). The device contains high-frequency channels of current and voltage of the zero sequence, the inputs of which are respectively the inputs of current and voltage signals of the zero sequence, a low-frequency channel of voltage of the zero sequence, the input of which is connected to the input of the voltage signal of the zero sequence, a circuit for generating the result of the comparison of the phases of the high-frequency signals connected to the outputs of the high-frequency channels, an adjustable delay circuit connected to the outputs of the result formation circuit cf phase of the high-frequency signals to the output of the low-frequency channel, and to the input of the alarm generation circuit, the output of which is the output of the device.

The principle of operation of the device is to use a high-frequency signal for overcharging the phase capacitances of the network that occur at the very beginning of a single-phase earth fault. The device provides the selection and analysis of the first amplitudes of the signals of the high-frequency components of the current and voltage of the zero sequence that occur as a result of transients during an alternating arc fault to ground; fixes the excess of the selected amplitudes above the threshold value for signals of negative and positive polarity; fixes a phase shift between the first unipolar signals, records that the threshold value is exceeded by the voltage amplitude of the zero sequence and generates an alarm when the phase shift is equal to or close to 90 ° and the maximum allowable value is exceeded by the voltage amplitude of the zero sequence. The delay scheme allows you to change the duration of a given time interval, which allows you to take into account the duration of the transient during the SCR or, increasing it, take into account the time required to compensate for capacitive currents in a single-phase earth fault.

A disadvantage of the known device consists, first of all, in the reduction of selectivity to the interference signal due to the lack of means that provide a clear link in the case of OZZ of the fixed phase relationship between the signals of the high-frequency components of the current and voltage of the zero sequence at the moment the high-frequency current passes through zero to the measured amplitude of the low-frequency component zero sequence voltage. This is explained by the fact that both signals are input to the delay line at an arbitrary moment in time without timing in relation to each other. The time of their arrival is not fixed, i.e. the device does not take into account the time of their appearance one relative to the other. Lack of control over the simultaneity of their appearance can lead to a false response of the device by an interference signal, the source of which in this case can be both low-frequency and high-frequency channels.

In addition, in accordance with the Rules for the technical operation of power plants and networks of the Russian Federation, when the network is operating, the neutral voltage is zero only with complete symmetry of the phase conductivity relative to the ground. In normal mode, the natural asymmetry is due to the different arrangement of wires on the supports, the uneven distribution of capacitors in phases to protect rotating machines, coupling capacitors and other work of technological equipment. In addition, the consumer himself introduces an artificial neutral bias in some situations to ensure the network is operational. In the presence of asymmetry, a neutral bias occurs. As a result, distribution electric networks have such parameters as the maximum short-term neutral displacement level acceptable for a given network (up to two hours) and the long-term maximum neutral displacement level that is less than half the permissible short-term maximum level (Rules for the technical operation of electric stations and networks of the Russian Federation Federation / Ministry of Fuel and Energy of the Russian Federation, RAO "UES of Russia", M .: SPO OGRES, 1996, pp. 280-287, hereinafter PTE). Thus, with neutral offsets, it is allowed for a limited time that the voltage amplitude exceeds the zero sequence value corresponding to the operating mode of the network. Moreover, as follows from the PTE, these maximum values for the distribution network are known. In the low-frequency channel of the known device there are no means to control two levels of permissible voltage of the low-frequency signal. The ability to control only one value of the voltage amplitude of the zero sequence does not allow to take into account the presence of a possible neutral bias, and therefore does not allow to exclude unjustified disconnection of the network connection. In addition, in the event that the neutral offset is natural, the possibility of this fact in the known device is not taken into account at all. At the same time, the duration of transient processes after an OZZ depends on the amplitude of the excess of the low-frequency component of the zero-sequence voltage of the maximum permissible value: if, for example, we set the lower threshold as the maximum short-term neutral displacement acceptable for the distribution network (up to two hours), then the transient process after OZZ will end earlier, in comparison with the upper reference threshold - the permissible long-term maximum level of neutral displacement. It follows that the known device, in the presence of a neutral bias, does not feel the correct moment in time of the end of the transient process, which leads to the issuing of a signal about the presence of an SCR or with delay, or prematurely, which leads to a decrease in the reliability of the device, to unjustified disconnection of the network connection. The lack of tools to control two voltage levels of the low-frequency signal does not allow to take into account the possibility of the presence of a neutral offset acceptable by the PTE, and therefore does not allow to exclude unjustified disconnection of the network connection, i.e. reduces the reliability of the known device and increases the likelihood of a false positive protection, and also deprives the device of versatility.

The permissible long-term maximum level of neutral bias is less than half the permissible short-term maximum level. However, in distribution electric networks with a neutral bias, in which a voltage is established on the neutral, which corresponds to the permissible continuous maximum level of the neutral bias, fixing the excess of the lower level can also be a sign of OZZ. The lack of the device’s ability to control the changes in time of the permissible long-term maximum level of neutral bias reduces the reliability of protection against SCR, and therefore reduces the reliability of the device. In addition, with SCR at the beginning and at the end of the development of neutral voltage (at the beginning and at the end of the transient envelope), interference noise can be generated. The inability to track changes in the amplitude of the NPP during the SCR, starting from the lower level, taking into account the presence of noise, does not allow to tune out interference noise at the beginning and at the end of the envelope, which reduces the reliability of the device, the selectivity of the device with respect to the interference signal and increases the likelihood of false alarms.

In addition, in the known device, the duration of the time interval for monitoring the presence of OZZ is set discretely by restructuring the delay line for a particular network, which deprives the device of universality. At the same time, the device does not have the means to take into account the influence on the decision to issue a signal for the presence of a fault zone of self-eliminating short-term single-phase earth faults, the existence of which does not adversely affect the electrical network, as well as alternating fault zones and interference signals caused by the inclusion of powerful consumer loads, or the launch of high-voltage propulsion systems. As a result, the selectivity with respect to the interference signal is reduced, and therefore, the likelihood of false alarms is increased.

Thus, the analogue and prototype of the claimed device identified as a result of a patent search that implements a method of directional protection against a single-phase earth fault in an alternating current electric distribution network do not allow to achieve a technical result consisting in increasing the reliability of the device, in increasing the selectivity with respect to to an interference signal, in reducing the likelihood of false alarms, in ensuring the universality of the device.

The proposed method of directional protection against a single-phase earth fault in an alternating current electric network solves the problem of creating an appropriate method, the implementation of which allows to achieve a technical result, which consists in increasing the reliability of the method, in increasing the selectivity with respect to the interference signal and in reducing the likelihood of false alarms, in ensuring universality.

The essence of the invention “Method of directional protection against a single-phase earth fault in a distribution electric network of alternating current” consists in the fact that in case of a single-phase earth fault, a low-frequency component corresponding to the operating frequency is isolated from a voltage signal of zero sequence, in addition, high-frequency components are isolated from current signals and zero sequence voltages, measure the amplitudes of their first half-waves, compare the measurement results with the corresponding reference values and if there is a simultaneous excess over the reference values, the phase relationships between the signals of the high-frequency components of the current and the zero-sequence voltage are measured at the moment the high-frequency current passes through zero, in addition, the amplitude of the extracted low-frequency component of the zero-sequence voltage is measured, the obtained value is compared with the reference, the result is fixed, and when the phase angle is within the specified limits and if the reference value is exceeded, the low-frequency amplitude of the other component of the zero sequence voltage, an alarm is generated after a time interval that is set taking into account the time of existence of high-frequency transients during a single-phase earth fault and taking into account the time required to compensate for capacitive currents during a single-phase earth fault, new is that as the reference value for the amplitude of the low-frequency component of the voltage of the zero sequence take the maximum allowable and lower controlled value of the amplitude In this case, the maximum short-term neutral displacement acceptable for the distribution network is taken as the maximum allowable value of the amplitude of the low-frequency component, and the long-term maximum neutral displacement acceptable for the distribution network is taken as the lower controlled value of the amplitude of the low-frequency component, if, as a result of measurement phase relations between the signals of the high-frequency components of the current and voltage of the zero sequence since the high-frequency current passes through zero the phase angle is within the specified limits, the measurement result of the phase angle is fixed during the control time interval, the duration of which is set according to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value after which, during the control time interval, the amplitude of the extracted low-frequency component of the zero sequence voltage is measured, To do this, first check if the amplitude of the low-frequency component of the zero-voltage component exceeds the zero sequence of the lower monitored value and, if the excess of the lower monitored value is detected, the maximum maximum permissible value is exceeded by the amplitude of the low-frequency component of the zero sequence voltage if the fact of exceeding the maximum permissible value is recorded , then an alarm is generated after the moment of fixation through the time interval that is set, in addition, taking into account the time that allows you to tune from interference signals and self-eliminating single-phase earth faults.

The technical result in the claimed method of directional protection against a single-phase earth fault in a distribution electric AC network is achieved as follows. As is known from the literature, under the influence of atmospheric or transient switching processes in electrical systems, voltage waves arise, superimposed on the operating voltage of the phases. The overvoltage pulse created in this way can cause a phase-to-earth breakdown somewhere in the system in the place of weakened insulation - a single-phase earth fault. In a network, the arc at the point of fault in some cases (with a sufficient distance between the wire and the ground) burns unstable, periodically extinguishing and igniting again (sometimes, as the damage site is warmed up, the unstable burning of the arc becomes stable). Regardless of the cause, an earth fault causes an increase in phase voltage. The presence of high-frequency transients is also characteristic of the OZZ. Since the charge and discharge circuits in the SCR are equivalent oscillatory circuits, this causes a phase shift between the corresponding RF components of the current and voltage of the zero sequence equal to or close to 90 °.

In the inventive method, the conclusion about the presence of an earth fault is made by analyzing the amplitudes of the high-frequency components of the current and voltage of the zero sequence and phase relationships between them and simultaneously monitoring the amplitude of the low-frequency component of the voltage of the zero sequence at the operating frequency. For this, high-frequency components are isolated from the signals of the current and voltage of the zero sequence. This allows you to directly evaluate the parameters of the high-frequency component of the transient process, which poses the greatest danger to the network in case of OZZ. Measurement of the first half-wave of a high-frequency signal allows one to take into account its polarity, which increases the reliability of the analysis results and increases the reliability of the method.

Fixing the phase relationship between the high-frequency components (HFS) of the current and the zero-sequence voltages makes it possible to verify the presence of a phase shift between them close to or equal to 90 °, which is not only one of the signs of the presence of an SCR, but also ensures the selectivity of the claimed method with respect to the high-frequency signal interference, since it confirms the correspondence to each other of the selected RF components of the current and voltage of the zero sequence.

In addition, since the fixation of the phase relation is carried out at the moment the high-frequency current passes through zero, i.e. when the signal amplitude of the high-frequency component of the zero-sequence voltage must be maximum, this also provides the binding of the RF components of the current and the zero-sequence voltage, which also increases the selectivity of the proposed protection method with respect to the interference signal.

As shown above, in accordance with the Rules for the technical operation of power plants and networks of the Russian Federation, when the network is operating, the neutral voltage is zero only with complete symmetry of the phase conductivity relative to the ground. In normal mode, the natural asymmetry is due to the different arrangement of wires on the supports, the uneven distribution of capacitors in phases to protect rotating machines, coupling capacitors and other work of technological equipment. In addition, the consumer himself introduces an artificial neutral bias in some situations to ensure the network is operational. In the presence of asymmetry, a neutral bias occurs. As a result, distribution electric networks have such parameters as the maximum short-term neutral displacement level permissible for a given network (up to two hours) and the long-term maximum neutral displacement level that is less than half the permissible short-term maximum level (Rules for the technical operation of electric stations and networks of the Russian Federation / Ministry of Fuel and Energy of the Russian Federation, RAO "UES of Russia", Moscow: SPO OGRES, 1996, pp. 280-287, hereinafter PTE). Thus, with neutral offsets, it is allowed for a limited time that the voltage amplitude exceeds the zero sequence value corresponding to the operating mode of the network. Moreover, as follows from the PTE, these maximum values for the distribution network are known. The claimed method provides two reference values for the amplitude of the low frequency component of the zero-sequence voltage: as the reference value for the amplitude of the low-frequency component of the voltage of the zero sequence, the maximum allowable and lower controlled amplitude values are used, while the maximum allowable for the given network is taken as the maximum allowable amplitude of the low-frequency component short-term level of neutral displacement, and as the lower one we control second low frequency component amplitude values take maximum permissible continuous neutral displacement for a given network. Therefore, the claimed method allows you to control two voltage levels of the low-frequency signal. This allows you to take into account the possibility of a neutral bias permissible by the PTE, and therefore, allows to exclude unjustified disconnection of the network connection, i.e. increases the reliability of the method and reduces the likelihood of a false positive protection. In addition, this allows not only to take into account the possibility of neutral displacement, but also to control the value of neutral displacement acceptable for the distribution network via PTE, and therefore also allows to exclude unjustified disconnection of the network connection, which increases the reliability of the method and reduces the likelihood of false protection operation.

The permissible long-term maximum level of neutral bias is less than half the permissible short-term maximum level. However, in distribution electric networks with a neutral bias, in which a voltage is established on the neutral that corresponds to the permissible long-term maximum level of the neutral bias, fixing the excess of the lower level can also be a sign of OZZ. The presence in the claimed method of controlling the excess of the low-frequency component of the voltage of the zero sequence voltage with the permissible long-term maximum level of neutral bias allows one to adequately evaluate the transient process and respond to the possibility of the occurrence of an SCR, then monitoring over the course of the time interval the presence of exceeding the maximum permissible value of the amplitude of the low-frequency component of the zero-voltage voltage . This increases the reliability of protection against OZZ, and therefore, increases the reliability of the method. In addition, during the SCR at the beginning and at the end of the development of neutral voltage (at the beginning and at the end of the transient envelope), interference noise is generated. Tracking the change in the amplitude of the low frequency component of the zero sequence voltage below the permissible long-term maximum level of neutral bias is impractical, since this mode is valid for the network. Due to the introduction of a lower controlled value of the amplitude of the low-frequency signal, the claimed method makes it possible to track changes in the amplitude of the low-frequency signal during OZZ, starting from the level that practically cuts off noise, which allows you to tune out interference noise at the beginning and at the end of the envelope of the voltage generated during the OZZ and increases reliability, selectivity method with respect to the interference signal, reduces the likelihood of false positives.

Moreover, despite the fact that the controlled levels of the low-frequency component of the zero sequence voltage correspond to a network with a neutral bias, the claimed method also works in networks with no neutral bias. This gives the method versatility.

The ability to control the excess of the amplitude of the LF component of the zero-sequence voltage using two standards of the amplitude value allows you to take into account all possible neutral operating modes, as well as the individuality of the electrical network operation modes, which also gives the claimed method universality.

In addition, the claimed method provides, when determining the SCR, the possibility of clearly linking the recorded phase relationship between the signals of the high-frequency components of the current and the zero-sequence voltage at the time the high-frequency current passes through zero to the measured amplitude of the low-frequency component of the zero-sequence voltage. This is because in the claimed method, if, as a result of measuring the phase relations between the signals of the high-frequency components of the current and voltage of the zero sequence at the moment of passage of the high-frequency current through zero, the phase angle is within the specified limits, then the measurement result of the phase angle is fixed in the course of the control time interval. In this case, the amplitude of the extracted low-frequency component of the zero sequence voltage is measured during the control time interval. In this case, the duration of the control time interval is set corresponding to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value. All this together provides a binding of the fixed phase relationship between the signals of the high-frequency components of the current and voltage of the zero sequence at the time the high-frequency current passes through zero to the measured amplitude of the low-frequency component of the voltage of the zero sequence, and therefore, increases the reliability of the method, increases the selectivity with respect to the interference signal and reduces the likelihood of false positives.

In addition, since in the claimed method, the amplitude of the LF signal is measured only if the phase angle is within the specified limits, the result is taken into account the sequence of occurrence of signs of the SCR, i.e. it is taken into account that the first sign of the SCR is the occurrence of a high-frequency process, which confirms the fixation of the phase shift within specified limits (close to or equal to 90 °). As a result, the reliability of the method increases, since the likelihood of false positives decreases.

Identification of the signs of SCR at high and low frequencies with reference to their time provides the ability to control the simultaneity of the appearance of both signs of SCZ, which reduces the likelihood of false triggering by an interference signal, the source of which in this case can be both low-frequency and high-frequency channels.

Due to the fact that in the claimed method, the presence of an excess of the low-frequency component of the voltage of the zero-sequence voltage of the zero sequence of the lower controlled value is first checked, this allows us to make the right decision on further actions, since the absence of the excess allows us to assume that the phase was fixed by the interference signal. Fixing the excess of the lower monitored value, as already shown above, can be a sign of both SPL and interference. Therefore, in case of fixing the excess of the lower monitored value, the presence of exceeding the maximum permissible value by the amplitude of the low-frequency component of the zero sequence voltage is monitored during the control time interval. Since the value of the control time interval is selected corresponding to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value, this ensures the reliability of the control results and reduces the likelihood of unjustified disconnection of the network connection, and therefore increases the reliability of the method, reduces the likelihood of false positives protection and increases selectivity with respect to the interference signal. In addition, the duration of the control interval can be set corresponding to the average statistical rise time of the voltage amplitude of the zero sequence during OZZ obtained by the inventors as a result of the study of various electrical networks, which is approximately 3 ms. This allows you to use one common control time interval for any neutral operation modes (with isolated neutral, with resistive, partially or fully compensated neutral), regardless of the presence of differences in individual parameters, which makes the method universal.

Due to the fact that in the inventive method, in the case of fixing the fact that the maximum permissible value is exceeded by the amplitude of the low-frequency component of the zero-sequence voltage, the alarm signal is generated after the moment of fixation through a time interval that is set taking into account the time of existence of high-frequency transients during a single-phase earth fault and taking into account the time, necessary to compensate for capacitive currents in case of a single-phase earth fault, and also which is set taking into account the time allowing to get rid of interference signals and self-eliminating single-phase earth faults, the selectivity of the method with respect to the interference signal is increased and the probability of false protection tripping is reduced, which increases the reliability of the method. The ability to set the time interval for generating an alarm for all cases of the neutral operating mode, as well as taking into account the time that allows you to tune out interference signals and self-eliminating single-phase earth faults, gives the claimed method universality.

From the foregoing, it follows that the claimed technical result in the proposed method of directional protection against a single-phase earth fault in an electrical distribution AC network is achieved as follows:

the method is based on the analysis of the amplitudes of the high-frequency current signals and the zero sequence voltage, the determination of the phase angle between the VHS current and the zero sequence voltage when the high frequency current passes through zero, the amplitude control of the low-frequency component of the zero sequence voltage. In this case, the decision on the presence of an OZZ is made on the basis of the following: the presence of an excess of the amplitudes of the high-frequency signals; the phase angle between the VPS current and the zero sequence voltage is within or equal to 90 °; the voltage amplitude of the zero sequence exceeds the minimum and maximum allowable values, which was absent in the prototype; the phase angle and the excess voltage amplitude of the zero sequence of the maximum allowable value recorded in the control time interval, which was absent in the prototype. Thus, in comparison with the prototype, the claimed method, when determining the SCR, takes into account the possibility of a neutral bias and provides the possibility of clearly linking the fixed phase relationship between the signals of the high-frequency components of the current and the zero-sequence voltage at the moment the high-frequency current passes through zero to the measured amplitude of the low-frequency component of the zero-sequence voltage . This is possible due to the fact that the result of measuring the phase angle (within or equal to 90 °) is fixed during the control time interval, the duration of which is set to the corresponding time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value. In this case, the maximum allowable excess of the low-frequency component of the voltage of the zero sequence amplitude is monitored during the control time interval. This ensures the reliability of the method, selectivity to interference signals and reduces the likelihood of false positives.

In addition, the claimed method allows you to control two voltage levels of the low-frequency signal. In this case, the maximum short-term neutral displacement acceptable for a given network is taken as the maximum allowable value of the amplitude of the low-frequency component, and the long-term maximum neutral neutral tolerance acceptable for this network is taken as the lowest controlled value of the low-frequency component amplitude. This allows you to take into account the possibility of a neutral bias permissible by the PTE, and therefore, allows to exclude unjustified disconnection of the network connection, i.e. increases the reliability of the method and reduces the likelihood of a false positive protection. The ability to control the excess of the amplitude of the low-frequency component of the zero-sequence voltage using two standards of the amplitude value allows you to take into account all possible neutral operating modes, as well as the individuality of the electrical parameters of the network, which ensures the reliability of the method, selectivity to interference signals and reduces the likelihood of false alarms, and also gives the declared way versatility.

Thus, from the foregoing, it follows that the claimed method of directional protection against a single-phase earth fault in an alternating current electric distribution network ensures the achievement of a technical result consisting in increasing the reliability of the method, in increasing the selectivity with respect to the interference signal and in reducing the likelihood of false alarms , and also ensures the achievement of a technical result, which consists in the versatility of the method.

A device for implementing the method of directional protection against a single-phase earth fault in an alternating current electrical distribution network, which implements the claimed method, solves the problem of creating an appropriate device, the implementation of which allows to achieve a technical result, which consists in increasing the reliability of the device, in increasing selectivity with respect to the interference signal , in reducing the likelihood of false positives, in ensuring the versatility of the device.

The inventive device for implementing a method of directional protection against a single-phase earth fault in a distribution electric network of alternating current "consists in that the device for implementing a method of directional protection against a single-phase earth fault in a distribution electric network of alternating current, containing high-frequency current channels and zero sequence voltage, the inputs of which are respectively the input of the zero sequence current signal and the voltage input zero-sequence, while the high-frequency channels are identical, the low-frequency channel of the zero-sequence voltage, the input of which is connected to the input of the zero-sequence voltage signal, is a phase-sensitive element, the inputs of which are connected from the first to the fourth, respectively, the outputs of the positive and negative polarity of the first half-wave of the high-frequency signals of the current channels and zero sequence voltage, and the alarm generation circuit, the output of which is the output ohms of the device, an additional control circuit for the low-frequency channel of the zero sequence voltage (CI), the first to fourth delay time drivers, the first OR element, a phase detection result reset circuit (SFC) are introduced, the control blocking signal output and the shapers outputs are connected to the inputs of the first OR element, the output of which is connected to the input blocking phase-sensitive element, the information inputs of the first driver of the delay time are connected to the outputs of the high-frequency channel current zero sequence, and the output is connected to its own input of the operation blocking and to the first input of the SFD, the output of which is connected to the cancellation input of the second delay time former, the input of which is connected to the output of the phase-sensitive element, and the output is also connected to the information input of the fourth time former delays, while the inverse output of the second driver is connected to the input of the reference resolution of the third driver, the information input of which is connected to the output of the fourth the shaper and to the second input of the SFD, while the input of the reference resolution of the fourth shaper and the output are connected respectively to the output and the second input of the control unit, the first input of which and the input of the countdown of the fourth shaper are connected to the output of the low-frequency channel of the zero sequence voltage, the control input of which is connected to the control output SU, in addition, the output of the third driver is connected to the input of the alarm signal generating circuit, while the low-frequency voltage channel is zero nosti comprises serially connected full-wave rectifier, a first low-pass filter and threshold element with galvanic separation and controllable response threshold, the rectifier input is the input of the low frequency channel output and the control input of the threshold element - respectively the output and the control input of the channel. In addition, the phase-sensitive element contains the first and second D-triggers and the second OR element, the inputs of which are connected to the outputs of the triggers, and the output is the output of the phase-sensitive element, while the C- and D-inputs of the first trigger are connected to the positive polarity outputs of the first half-wave of high-frequency signals channels of current and voltage of the zero sequence, and C- and D-inputs of the second trigger are connected to the outputs of the negative polarity of the first half-wave of high-frequency signals of channels of current and voltage of the zero trace functions, respectively, while the R-inputs of the triggers are connected and are the blocking input of the phase-sensitive element. Moreover, the control circuit of the low-frequency channel of the zero-voltage voltage contains a fifth delay driver, a second low-pass filter, a delay line, a third D-trigger, an element NOT, an element AND, and a third OR element, and the input of the element is NOT the first input of the control system and is connected to the input canceling the count of the fifth driver, in addition, the output of the element is NOT connected to the input of the second low-pass filter and to the inputs of the resolution of the third D-trigger and the fifth driver, the output of which is connected to the input of the link and a delay, the output of which is connected to the first input of the third OR element, the second input of which is the second input of the control unit, and the output is the output of the lock signal of the control unit, in addition, the information input of the fifth driver is connected to the signal source of a single level, and the output of the third element is connected, in addition, to the input of the countdown of the third D-flip-flop, the information input of which is connected to the signal source of the unit level, and the output is the control output of the control system and, in addition, is connected to the first input of the element And that, the second input of which is connected to the output of the second low-pass filter, and the output is the output of SR. Moreover, the phase detection result reset circuit (SFD) contains a short pulse shaper and an OR-NOT element, the input of a short pulse shaper is the first input of the SFD, the first input of the OR-NOT element is the second input of the SFD, the second input of the OR-NOT element is connected to the output of the shaper short pulses, and the output of the OR-NOT element is the output of the SFD. In the low-frequency channel of the zero-sequence voltage, the threshold element with a controlled response threshold contains an npn transistor, in which a resistor is connected in parallel to the base-collector junction, and a first zener diode is connected in series to the base, to which a second zener diode is connected in series, to which a control key is connected, an open contact which is connected to the control input of the LF channel, and minus the second zener diode is connected to the output of the LF channel.

The technical result in a device that implements the claimed method is achieved as follows. As described above, from the literature it is known that under the influence of atmospheric or transient switching processes in electrical systems, voltage waves appear, superimposed on the operating voltage of the phases. The overvoltage pulse created in this way can cause a phase-to-earth breakdown somewhere in the system in the place of weakened insulation - a single-phase earth fault. In a network, the arc at the point of fault in some cases (with a sufficient distance between the wire and the ground) burns unstable, periodically extinguishing and igniting again (sometimes, as the damage site is warmed up, the unstable burning of the arc becomes stable). Regardless of the cause, an earth fault causes an increase in phase voltage. The presence of high-frequency transients is also characteristic of the OZZ. Since the charge and discharge circuits in the SCR are equivalent oscillatory circuits, this causes a phase shift between the corresponding high-frequency (HF) components of the current and voltage of the zero sequence, equal to or close to 90 °. The principle of operation of the claimed device, which implements a method of directional protection against a single-phase earth fault in an alternating current distribution electric network, consists in analyzing the amplitude of the signals of the high-frequency components of the current and voltage of the zero sequence during the SCR, in analyzing the phase relationships between them and controlling the amplitude of the low-frequency component of the voltage zero sequence at the time when the phase shift between the corresponding high-frequency (HF) components of the current and yazheniya zero sequence equal or close to 90 °.

The presence in the device of high-frequency channels of current and zero sequence voltage (HPS 3i ₀ and HFS 3u ₀ ) and a low-frequency channel of zero sequence voltage (3u ₀ ) allows us to estimate the parameters of high-frequency components of current and voltage of zero sequence at the beginning of the SCR, which are characteristic of the SCR, and also evaluate the magnitude of the LF component of the neutral voltage in this situation, which ensures the reliability of the device, selectivity with respect to the interference signal and reduce the likelihood of false positives atyvany.

Due to the fact that the channels of the RFL 3i ₀ and RFL 3u ₀ are identical, the phase relations between the RFL 3i ₀ and RFL 3u ₀ signals are provided at the inputs of the phase-sensitive element, which increases the selectivity of the device with respect to the interference signal. The presence in the RF channels of the outputs of the negative and positive polarity of the first half-wave of high-frequency signals takes into account the random nature of the polarity of the high-frequency signals, and also allows you to fix the beginning of the high-frequency transient, i.e. the beginning of OZZ, which ensures the reliability of the device.

The phase-sensitive element provides control of the phase relations between the recorded unipolar amplitudes of the RF signals 3i ₀ and the RF 3u ₀ signals, and provides the possibility of fixing a phase ratio close to or equal to 90 °, which ensures selectivity with respect to the interference signal. The construction of a phase-sensitive element on two D-flip-flops, the first and second, allows you to fix the phase relationship at the moment of passage through zero of the RFS 3i ₀ , moreover, for both polarities of the signals, the RFL 3i ₀ and the RFL 3u ₀ . For this, in one of the triggers, the D- and C-inputs are connected to the negative polarity outputs of the first half-wave of high-frequency signals, and in the other, to the positive polarity outputs, which takes into account the random polarity of the amplitude of the high-frequency signal, increases the reliability of the device and provides selectivity with respect to interference signal. In this case, the D-inputs are connected to the outputs of the high-frequency channel of the zero-sequence voltage, and the C-inputs are connected to the outputs of the high-frequency channel of the zero-sequence current, which makes it possible to fix the phase relationship between the unipolar VPS 3i ₀ and VPS 3u ₀ , close to or equal to 90 ° when passing current through zero. This provides selectivity for the interference signal. In addition, the construction of a phase-sensitive element on the first and second D-flip-flops provides the ability to control its operation, namely, it is possible to block it by R-inputs to prevent the possibility of operation from an interference signal, which increases the noise immunity of the device and, therefore, increases its reliability. The ability to block the phase-sensitive element from being triggered by an interference signal prevents unreasonable disconnection of undamaged network connections, which reduces the likelihood of false positives. The second OR element, the inputs of which are connected to the outputs of the first and second D-flip-flops, and the output is the output of the phase-sensitive element, provides the possibility of obtaining the result of detecting signals of either positive or negative polarity, which takes into account the polarity of high-frequency signals and increases the reliability of the device. The possibility of fixing a phase shift close to or equal to 90 ° between the VPS 3i ₀ and VPS 3u ₀ reduces the likelihood of a false alarm, since in this case a phase shift close to or equal to 90 ° serves as a reference to the useful signal. In addition, the proposed implementation and connection of the phase-sensitive element to the outputs of the RF channels makes it possible to fix a phase shift equal to or close to 90 ° when the RFI 3i ₀ passes through zero, i.e. when the amplitude of the high frequency voltage signal of the zero sequence is maximum. It also provides a snap to the desired signal. As a result, the reliability of the device, the selectivity with respect to the interference signal are increased, and the likelihood of false alarms is reduced.

The low-frequency (LF) channel of the zero-sequence voltage, which consists of a half-wave rectifier, the first low-pass filter, a threshold element with galvanic isolation and a controlled threshold, provides during OZZ the ability to control the amplitude of the low-frequency component of the voltage of the zero sequence, which increases the selectivity with respect to the interference signal and reduces the number of false positives, and therefore increases the reliability of the device.

The introduction of a half-wave rectifier into the LF channel during OZZ provides the ability to control the amplitudes of half-waves of the LF component of the zero sequence voltage of both polarities, which was not in the prototype. This increases the information content, and therefore, the reliability of the device. The low-pass filter isolates the working frequency signal from the signal arriving at its input and cuts off the interference signals, which increases the selectivity of the device with respect to interference. The introduction of a threshold element with galvanic isolation into the NPF channel also increases the stability of the device with respect to interference, since it galvanically decouples the threshold element from the metal parts of the device housing and other elements and components of the device, which eliminates the effect of the induced signal on the threshold element from the electrical connections between the elements and device nodes, and therefore, eliminates the possibility of a threshold element from an interference signal, which also increases the selectivity of the device in relation to the interference signal.

In addition, it is known that, in accordance with the Rules for the Technical Operation of Power Plants and Networks of the Russian Federation, when the network is operating, the neutral voltage is zero only with complete symmetry of the phase conductivity relative to the ground. In normal mode, the natural asymmetry is due to the different arrangement of wires on the supports, the uneven distribution of capacitors in phases to protect rotating machines, coupling capacitors and other work of technological equipment. In addition, the consumer himself can, if necessary, ensure the operability of the network, introduce a neutral offset artificially. In the presence of asymmetry, a neutral bias occurs. As a result, distribution electric networks have such parameters as the maximum short-term neutral displacement level acceptable for a given network (up to two hours) and the long-term maximum neutral displacement level that is less than half the permissible short-term maximum level (Rules for the technical operation of electric stations and networks of the Russian Federation Federation / Ministry of Fuel and Energy of the Russian Federation, RAO "UES of Russia", M .: SPO OGRES, 1996, pp. 280-287, hereinafter PTE). Thus, with neutral offsets, it is allowed for a limited time that the voltage amplitude exceeds the zero sequence value corresponding to the operating mode of the network. Moreover, as follows from the PTE, these maximum values for the distribution network are known. The introduction of a threshold element with a controlled response threshold into the LF channel of the device allows you to take into account the possibility of neutral bias by setting two thresholds: the maximum allowable value of the amplitude of the low-frequency component, which is set equal to the maximum short-term level of neutral bias acceptable for the distribution network, and the lower controlled value of the amplitude of the low-frequency component, which is set equal to the permissible continuous maxi low neutral bias level. Such an approach to the selection of thresholds for the operation of a controlled threshold element allows us to take into account the possibility of a neutral bias, and therefore, eliminates the unjustified disconnection of the network connection, i.e. increases the reliability of the device and reduces the likelihood of a false positive protection. When constructing a threshold element with a controlled response threshold, the principle of changing the operating mode of the transistor by controlling the operating mode of the base circuit is used. This is achieved by introducing a transistor into the threshold element, in which a resistor is connected in parallel to the base-collector junction, and the first zener diode is connected in series to the base, to which the second zener diode is connected in series, to which the control key is connected, which allows connecting both zener diodes to the base or one , adjust the collector current - base. In this case, the NC contact of the control key is connected to the control input of the low-frequency channel, which makes it possible to change the operation mode of the transistor according to the control signal from the control system. Due to the fact that the minus of the second zener diode is connected to the output of the low-frequency channel, a signal is generated at the output of the low-frequency channel to fix the excess of the lower controlled or maximum allowable amplitude of the low-frequency signal when the voltage across the collector of the transistor changes.

The permissible long-term maximum level of neutral bias is less than half the permissible short-term maximum level. However, in distribution electric networks with a neutral bias, in which a voltage is established on the neutral that corresponds to the permissible long-term maximum level of the neutral bias, fixing the excess of the lower level can also be a sign of OZZ. The presence in the claimed method of controlling the excess of the LF amplitude of the voltage component of the zero sequence of the permissible long-term maximum level of neutral bias allows you to adequately evaluate the transient process and respond to the possibility of the occurrence of an SCR in accordance with the development of the transient process, which increases the reliability of protection against SCR, and therefore, increases the reliability of the method . In addition, the ability to control the lower voltage level in networks with a neutral offset increases the reliability of the device. This is due to the fact that the moment of exceeding the controlled voltage level is perceived by the device as a voltage surge ending in a transient process. At this point, high-frequency channels extract high-frequency components of current and voltage from signals of the zero sequence. At the same time, when the lower controlled level of the LF component of the zero-sequence voltage is exceeded, a phase shift between the high-frequency components of the current and the zero-sequence voltage, close to or equal to 90 °, can be fixed, which is one of the signs of the presence of SCR. However, the presence of a second triggering threshold of a controlled threshold element provides the ability to control further voltage exceeding the maximum value, and in its absence, the device does not generate a signal about the presence of an SCR. As a result, unreasonable disconnection of the network connection is excluded, which increases the reliability of the device, selectivity to the interference signal and reduces the likelihood of false positives.

In addition, during the SCR at the beginning and at the end of the development of the neutral voltage (at the beginning and at the end of the envelope of the voltage developing during the SCR), interference noise can be generated. The ability to monitor changes in the amplitude of the low-frequency signal during OZZ, starting from a predetermined lower level, below which (below the permissible long-term maximum level of neutral bias), the operating mode for the network is permissible; a voltage signal generated during OZZ, which increases the reliability of operation, the selectivity of the device with respect to the interference signal and reduces the likelihood of false positives.

At the same time, despite the fact that the controlled levels of the low-frequency component of the zero sequence voltage correspond to networks with a neutral bias, they are optimal for distribution networks with no neutral bias. This gives the device versatility.

As a result, the introduction of a threshold element with a controlled response threshold into the LF channel allows us to take into account the possibility of a network neutral offset, which eliminates unjustified disconnection of the network connection, i.e. increases the reliability of the device and reduces the likelihood of a false positive protection. Moreover, the values of the thresholds are universal, which ensures the universality of the device.

The control circuit of the low-frequency channel of the zero sequence voltage (CS) generates a control signal for the controlled threshold element, providing the possibility of sequential control of its threshold. This allows you to take into account the presence of a network neutral offset by setting the required response threshold, increases the reliability of the device, and also gives the device universality. In addition, at its output, the control system generates information about the presence of exceeding the maximum allowable value by the amplitude of the low-frequency component of the zero-sequence voltage, which is one of the main signs of the OZZ and ensures the reliability of the device. With OZZ, the control circuit generates a device blocking signal, block its operation from the interference signal until the transients in the LF channel end, which increases the reliability of operation, selectivity with respect to the interference signal and reduces the likelihood of false positives.

Introduction to the device shapers delay time from the first to the fourth allows you to generate time delays that ensure the selectivity of the device relative to the interference signal. By connecting the outputs of all the formers and the control lock output through the first OR element to the phase-sensitive blocking input, in the process of analyzing the signals characteristic of the OZZ, the device is sequentially blocked from possible operation by an interference signal, which is especially important for undamaged network connection, as it eliminates its unjustified shutdown, and therefore reduces the likelihood of false positives.

Introduction to the device of the first driver of the delay time, the information inputs of which are connected to the outputs of the high-frequency channel of the zero-sequence current channel, and the output is connected to its own input of the operation blocking and to the first input of the SFD and, through the first OR element, to the blocking input of the phase-sensitive element, protects the device from non-selective operation with respect to the interference signal of the high-frequency channel of the zero sequence current channel. The first driver is triggered on the trailing edge of the high-frequency signal of the zero sequence current, blocking the phase-sensitive element through the first OR element for the generated delay time, after the latter is triggered. Blocking of the phase-sensitive element by the output signal of the first driver of the delay time also occurs when partial discharges in the insulation or in the presence of interference in the RF signal of the zero-sequence current, which increases the selectivity and reliability.

The second delay time former provides registration of the fact of the operation of the phase-sensitive element, fixing it for a period of up to 1.5 s and, at the same time, through the element OR blocking of the phase-sensitive element. At the same time, the introduction of the delay time generated by the second shaper provides detuning from short-term self-liquidating OZZ, as well as from interference caused by switching on powerful consumer loads or starting high-voltage propulsion systems, with a duration range from 0.012 to 1.5 s (0.012 s is the minimum time for detuning from ferroresonance processes; 1.5 s is the total statistical time at which propulsion systems complete the launch). This increases the reliability of the device, selectivity with respect to the interference signal and reduces the likelihood of false positives.

The introduction of the fourth delay time driver, the reference resolution input of which is connected to the control system output, provides information on the presence or absence of exceeding the maximum allowable value by the amplitude of the low-frequency component of the zero sequence voltage. Due to the connection between the output of the LF channel and the input for canceling the counting of the fourth shaper, the output signal of the LF channel allows, if there is an excess of the maximum allowable value, the amplitude of the LF component of the voltage of the zero sequence, or prohibits, in its absence, the operation of the fourth and fifth (in the control circuit) time shapers. Due to the fact that the information input of the fourth driver is connected to the output of the second driver, which contains information about the presence of a phase-sensitive element, the fourth driver, if there is an excess of voltage in the LF channel and there is a phase shift within the specified limits, sets an active signal at its output.

In this case, the achievement of the technical result by the introduction of a control circuit is provided as follows. In the control system, the element does NOT invert the input signal coming from the output of the low-frequency channel to the first input of the control system to ensure the operability of the fifth delay driver and the third D-trigger according to the output signal of the low-frequency channel. As a result, the third D-flip-flop detects the presence of an excess of the low-frequency signal amplitude of the lower controlled level and generates at the control output of the control signal the control threshold of the triggered threshold element in the low-frequency channel (communication of the control output of the control with the control input of the low-frequency channel), briefly increasing it to the maximum allowable. This allows you to monitor a further change in the amplitude of the LF signal and record during this time the presence of exceeding the maximum allowable value. Due to the fact that the second low-pass filter is triggered only when the amplitude of the low frequency signal exceeds the upper threshold of the controlled threshold element, it is possible to fix the excess. The And element, by connecting its inputs to the outputs of the second low-pass filter and the third D-trigger, generates a reference signal for the fourth driver at the moment of fixing the excess of the upper threshold. The signal enters the fourth shaper due to the connection of the output of the control system with the input of the resolution reference of the shaper. In the presence of 033, due to the connection of the output of the fourth shaper with the second input of the control system, the signal from the output of the fourth shaper brings the control system to its initial state (D-trigger is reset; the fifth shaper is reset by the signal from the first input of the control system), at which the lower threshold of the controlled threshold is set in the low-frequency channel item.

In the absence of a signal from the output of the fourth shaper in the LF channel, the upper threshold of the controlled threshold element is held for a predetermined time due to the delay line. The latter allows you to set the delay time - the control time interval equal to the average, during which during the SCR the amplitude of the low-frequency component of the zero sequence voltage reaches a value that exceeds the maximum allowable. As a result, it is possible to control the amplitude of the low frequency component of the zero sequence voltage in networks with different parameters from each other. This increases the reliability of the device, and also gives it versatility.

After the lower threshold of the controlled threshold element is set in the LF channel, the further triggering of the threshold element occurs from each half-wave of the low-frequency voltage signal of the zero sequence, until the amplitude exceeds the lower controlled level. As a result, due to the connection of the output of the LF channel with the cancellation inputs of the fourth and fifth shapers of the delay time, it is prohibited to count the time of these shapers for the entire duration of the transition process in the LF channel, which increases the selectivity of the device with respect to the interference signal.

In the absence of an SCR, the control circuit sets the device blocking signal at its output after the time formed by the delay line. This is ensured by connecting the fifth shaper to the first input of the control system (LF channel output) by the input of counting cancellation, and, through the element NOT, by the resolution enable input, and by connecting the fifth shaper to the delay line in series. The delay time of the fifth shaper provides the ability to take into account the time duration of the transient in the LF channel. This ensures reliable blocking of the phase-sensitive element by the control signal output, which excludes the device from tripping in recovery mode and, therefore, excludes the possibility of unjustified shutdown of the network, reduces the likelihood of false positives, increases the reliability of the device and increases the selectivity to interference. Moreover, the introduction of a delay line allows you to set almost any length of the control time interval for tracking the change in the amplitude of the low-frequency component of the zero sequence voltage. This makes it possible to set the duration of the control time interval equal to the average statistical time obtained by the authors as a result of studying various electrical networks, during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum allowable value - about 3 ms. This allows you to take into account the operating mode of the neutral, differences in the individual parameters of the distribution networks, which allows to obtain a technical result, which consists in ensuring the universality of the device, and also increases the reliability of the device.

Only if there is a phase shift between the RF signals of the current and voltage of the zero sequence within the specified limits, the fourth driver of the delay time generates a signal about the presence of the voltage amplitude exceeding the zero sequence of the maximum allowable value. In this case, the time delay of the fourth driver takes into account the duration of the transient in the LF channel, which ensures reliable recording of information about the amplitude of the LF signal and increases the selectivity of the device with respect to the interference signal. In addition, due to this, blocking signals generated by the output signal of the fourth driver (SU lock output and the fourth signal output of the fourth driver) provide reliable blocking of the phase-sensitive element during SCR, which excludes the device from tripping in unlock mode and increases the selectivity to interference.

Moreover, due to the connection of the information input of the fourth shaper with the output of the second shaper, the signal is generated in time of the appearance of the signal when the amplitude of the zero sequence voltage exceeds the maximum permissible value and the phase shift is fixed within the specified limits between the RF components of the current and the zero sequence voltage, which was not in the prototype. As a result, the reliability of the device, the selectivity to interference signals, and the likelihood of false alarms are reduced.

The third pulse shaper, due to its connections with the circuit elements of the device, transmits an alarm to the input of the alarm generation circuit while maintaining the signs of OZZ at its input and holds it at the circuit input for the delay time it generates, which takes into account the occurrence of interference signals when the contacts of the actuating relay of the circuit alarm generation. As a result, the reliability of the device increases, selectivity to interference signals and the likelihood of false alarms is reduced. At the same time, at the output of the alarm signal generating circuit, an output signal is generated about the presence of an OZZ duration determined by the delay time of the third driver.

Due to the claimed connections, the phase detection result (SFC) reset circuit cancels, after the delay time of the first driver, the detection result of the phase-sensitive element if it is triggered by high-frequency interference if the maximum allowable threshold is not exceeded by the amplitude of the low-frequency component of the zero-sequence voltage. It also increases the selectivity of the device with respect to the interference signal, reduces the likelihood of false alarms and increases the reliability of the device. In this case, the short-pulse shaper, due to communication with the first input of the circuit, generates a reset pulse for the second shaper by cutting the pulse from the output of the first shaper (i.e., after the delay time of the first shaper) in the absence of a second input of the circuit (second input of the OR element NOT) a signal that the maximum permissible value is exceeded by the amplitude of the LF component of the zero sequence voltage.

Thus, in the claimed device, due to the claimed implementation, the decision on the presence of an OZZ is made on the grounds of: the presence of an excess of the amplitudes of the high-frequency signals; the phase angle between the VPS current and the zero sequence voltage is within or equal to 90 °; the voltage amplitude of the zero sequence exceeds the minimum and maximum allowable values, which was absent in the prototype; the phase angle and the excess of the zero sequence voltage amplitude of the maximum permissible value are fixed in the control time interval, the duration of which is set equal to the average statistical time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value, which was also absent in the prototype. As a result, in comparison with the prototype, the claimed device, when determining the SCR, takes into account the possibility of a neutral bias and provides a clear link to the measured amplitude of the LF component of the zero-sequence voltage of the recorded phase shift between the signals of the HF components of the current and zero-sequence voltage at the moment the high-frequency current passes through zero .

The presence of first-to-fifth delay time formers and their connections with other elements of the device circuit provides the possibility of establishing a time interval for generating an alarm for any variants of the neutral operating modes and individual distribution network parameters, taking into account the existence of high-frequency transient processes during a single-phase earth fault, with taking into account the time required to compensate for capacitive currents with a single-phase earth fault, taking into account interference signals and self-cleaning yuschihsya single-phase earth fault, which allows the use of the claimed device to protect all electric distribution networks. The result is the achievement of a technical result, which consists in the universality of the device.

Thus, from the foregoing, it follows that the proposed device for implementing the method of directional protection against a single-phase earth fault in an electric alternating current network, which implements the claimed method, allows to achieve a technical result, which consists in increasing the reliability of the device, in increasing selectivity with respect to interference signal, in reducing the likelihood of false alarms, in ensuring the universality of the device.

Figure 1 shows a block diagram of a device for implementing a method of directional protection against a single-phase earth fault in an electrical distribution AC network; figure 2 is a circuit diagram of the control circuit of the low-frequency channel voltage zero sequence; figure 3 is a diagram of an electrical circuit reset the result of phase detection; 4 is a diagram of an electrical threshold element with a controlled threshold.

A device for implementing the method of directional protection against a single-phase earth fault in an alternating current distribution electric network contains identically executed high-frequency channels 1, 2 of current and zero-sequence voltage, the inputs of which are respectively the input of the zero-sequence current signal and the input of the zero-sequence voltage signal; a low-frequency channel 3 voltage of the zero sequence, the input of which is connected to the input of the voltage signal of the zero sequence; phase-sensitive element 4, the inputs of which are connected from the first to the fourth, respectively, the outputs of positive 5, 6 and negative 7, 8 polarity of the first half-wave of high-frequency signals of current channels and zero-sequence voltage, respectively; alarm generating circuit 9, the output of which is the output of the device; the control circuit 10 of the low-frequency channel 3 voltage zero sequence (SU); shapers delay time from the first 11 to the fourth 14, the first element OR 15, circuit 16 reset the result of phase detection (SFD). The output 17 of the lock signal SU 10 and the outputs of the shapers are connected to the inputs of the first element OR 15, the output of which is connected to the input of the blocking of the phase-sensitive element 4. The information inputs of the first 11 shaper of the delay time are connected to the outputs 5, 7 of the high-frequency channel of the zero sequence current, and the output is connected to own input lock operation and to the first input of the SFD 16, the output of which is connected to the input of the cancellation of the countdown of the second 12 shaper time delay, the input of which is connected to the output of of the sensing element 4, and the output, in addition, is connected to the information input of the fourth 14 of the delay time former. In this case, the inverse output of the second 12 shaper is connected to the input of the reference resolution of the third 13 shaper, the information input of which is connected to the output of the fourth 14 of the shaper and the second input of the SFD 16. The input of the resolution resolution of the fourth 14 of the shaper and the output are connected respectively to the output 18 and the second input 19 of the control system 10, the first input of which 20 and the cancellation input of the fourth fourth shaper are connected to the output of the low-frequency channel of the zero sequence voltage, the control input of which is connected to the control SU present output 10. Output 21 of the third generator 13, connected to the input circuit 9 is the formation of an alarm.

The low frequency voltage channel 3 of the zero-sequence voltage comprises a half-wave rectifier 22, a first low-pass filter 23 and a threshold element 24 with galvanic isolation and a controlled threshold that are connected in series. The input of the rectifier 22 is the input of the low-frequency channel 3, the output and the control input of the threshold element 24 is the output and the control input of the channel, respectively.

The phase-sensitive element 4 contains the first 25 and second 26 D-flip-flops and the second 27 element OR, the inputs of which are connected to the outputs of the triggers, and the output is the output of the phase-sensitive element. The C- and D-inputs of the first 25 flip-flops are connected to the positive polarity outputs 5, 6 of the first half-wave of high-frequency signals of current and voltage channels 1, 2 and the zero-sequence voltage, and the C- and D-inputs of the second trigger are connected to the negative polarity outputs 7, 8 of the first half-wave high-frequency signals of channels 1, 2 of the current and voltage of the zero sequence, respectively. The R-inputs of the triggers 25, 26 are connected and are the input blocking phase-sensitive element.

The control circuit 10 of the low-frequency voltage channel of the zero sequence voltage contains a fifth 28 delay time driver, a second low-pass filter 29 and 30 a delay line, a third D-trigger 31, an element NOT 32, an AND 33 element, and a third OR 34 element. The input of the NOT 32 element is the first 20 by the input of SU 10 and is connected to the input of counting cancellation of the fifth driver, in addition, the output of the element NOT 32 is connected to the input of the second low-pass filter 29 and to the inputs of the resolution of the third 31 D-trigger and fifth 28 of the driver, the output of which is connected to the input 30 of the rear A horn, the output of which is connected to the first input of the third 34th OR element, the second input of which is the second 19th input of the control unit 10, and the output is the output 17 of the lock signal of the control unit 10. The information input of the fifth 28 shaper is connected to the signal source of a single level, and the output of the third 34th element OR is connected, in addition, to the input of the countdown of the third 31 D-flip-flop, the information input of which is connected to the signal source of the unit level, and the output is the control output 21 of the control system 10 and, in addition, the element is connected to the first input And 33, a second input connected to the output of the second LPF 29 and the output 18 is the output of 10 SU.

The phase detection result (SFD) reset circuit 16 contains a short pulse shaper 35 and an OR-NOT element 36, the input of the pulse shaper 35 being the first input of the SFD 16, the first input of the OR element 36 is the second input of the SFD 16, and the second input of the OR element 36 - NOT connected to the output of the shaper 35 short pulses, and the output of the element 36 OR is NOT the output of the SFD 16.

The threshold element 24 with a controlled threshold of operation contains an npn transistor 37, in which a resistor 38 is connected in parallel with the base-collector junction, and the first is connected to the base in series with the first 39 zener diode, to which the second 40 zener diode is connected in series, in parallel with which the control key 41 is connected, opening contact which is connected to the control input of the LF channel, and minus the second zener diode is connected to the output of the LF channel.

The delay time formers from the first 11 to the fourth 14 and fifth 28 are single-shots that can be performed, for example, on pulse counters.

The alarm generating circuit 9 can be made in the form of an executive relay.

High-frequency channels 1, 2 of the current and voltage of the zero sequence are identical and can be performed in accordance with those described in the prototype (RF patent No. 2097893, H2N 3/16, 11/27/97). Each of the high-frequency channels 1, 2 contains a pre-filter connected in series, the input of which is the channel input, a high-pass filter and a circuit for extracting the first half-wave of a high-frequency signal, the first output of which is connected respectively to the first low-pass filter and the first threshold element, and the second output connected respectively to the second low-pass filter and the second threshold element connected in series, the outputs of the first and second threshold elements i are respectively the outputs of positive 5, 6 and negative 7, 8 polarity of the first half-wave of high-frequency current signals and zero sequence voltage.

In channels 1, 2, the preliminary filter provides filtering of the operating frequency, as well as the frequency band that is not included in the object of research. The high-pass filter provides the selection of the signal of the high-frequency component of the current (voltage) of the zero sequence, which is formed as a result of transients during an alternating arc fault to ground. The allocation scheme for the first half-wave of the signal takes into account the random nature of the initial phase and polarity of the analyzed high-frequency signal. Low-pass filters, the first and second, provide the final filtering of the desired high-frequency signal, filtering the pick-up signals. The presence of threshold elements, the first and second, provides the ability to control the excess of the amplitude of the high-frequency signal of the reference value for both positive and negative polarity, and also provides the normal operation of the subsequent elements of the device.

The method of directional protection against a single-phase earth fault in an electrical distribution AC network is implemented as follows.

In accordance with the claimed method, in the case of a single-phase earth fault, a low-frequency component corresponding to the operating frequency, high-frequency components from current signals and zero-sequence voltage are isolated from the zero-sequence voltage signal. The amplitudes of the first half-waves of the high-frequency components are measured. Compare the measurement results with the corresponding reference values and, if there is a simultaneous excess over the reference values, measure the phase relationship between the signals of the high-frequency components of the current and voltage of the zero sequence at the time of passage through zero of the high-frequency current. If, as a result of measuring the phase relations between the signals of the high-frequency components of the current and the voltage of the zero sequence, is within the specified limits, the result of measuring the phase angle is fixed during the control time interval. The duration of the control time interval is set corresponding to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value, which is about 3 ms. Then, during the control time interval, the amplitude of the extracted low-frequency component of the zero sequence voltage is measured. As a reference value for the amplitude of the low-frequency component of the voltage of the zero sequence take the maximum allowable and lower controlled value of the amplitude. In this case, the maximum short-term neutral displacement acceptable for a given network is taken as the maximum allowable value of the amplitude of the low-frequency component, and the long-term maximum neutral neutral tolerance acceptable for this network is taken as the lowest controlled value of the low-frequency component amplitude. First, the presence of an excess of the low-frequency component of the voltage of the zero-sequence voltage of the zero sequence of the lower monitored value is checked and, in the case of fixing the excess of the lower monitored value, the presence of the excess of the maximum permissible value of the amplitude of the low-frequency component of the voltage of the zero sequence is monitored. If the fact of exceeding the maximum permissible value is recorded, then the alarm signal is generated after the moment of fixation through the time interval, which is set taking into account the time of existence of high-frequency transients during a single-phase earth fault and taking into account the time required to compensate for capacitive currents during a single-phase earth fault, and also taking into account the time allowing to tune out from interference signals and self-eliminating single-phase earth faults, the average operating time of which is from 0.012 s to 1.5 s .

The claimed method implements a device of directional protection against a single-phase earth fault in a distribution electric AC network. The signals at the inputs of current and voltage of the zero sequence are supplied to the device from the corresponding transformers (not shown in Fig. 1). In the case of occurrence of a zero-sequence current and voltage signals at a controlled OZZ connection, high-frequency components appear that emit RF channels 1 and 2, information about which is set either at outputs 5, 6 of positive or at outputs 7, 8 of negative polarity of the first half-wave of high-frequency channel signals current 1 and voltage 2 of the zero sequence. At the moment the high-frequency signal of the zero sequence current passes through zero at the input C of the first 25 (second 26) D-trigger of the phase-sensitive element 4, information is recorded about the presence at the input D of the positive (negative) half-wave of the high-frequency component of the zero sequence voltage. When recording a single signal at input D at the output of the second element OR 27 of the phase-sensitive element, an active signal level appears.

After the phase-sensitive element 4 is triggered, by cutting off a high-frequency pulse of a zero-sequence current of negative or positive polarity (outputs of 5, 6 or 7, 8 RF channels), the first 11 delay time driver is started, which self-locks for its own delay time and simultaneously blocks it with its own the output signal is a phase-sensitive element 4. The signal from the output of the first 11 shaper blocks the phase-sensitive element also with partial discharges in the isolation of the network or in the presence of x in the zero-sequence current signals, thereby preventing its operation, and therefore, charging of the device for the intact network connection from the interference signal. Thus, as a result of the operation of the first 11 shaper at the first input of the SFD 16 during the delay time of the first shaper 11, there is information about fixing the excess of the high-frequency signal current of the zero sequence zero reference value.

The signal from the output of the phase-sensitive element 4 starts for a period of 1.5 s the second 12 delay time former, which starts the countdown. At the same time, an active level appears at the output of the second 12 shaper, which is set at the information input of the fourth 14 shaper. At the same time, the signal from the output of the second driver 12 through the first element OR 15 blocks the triggers 25, 26 of the phase-sensitive element 4 at the inputs R. As a result, the information input of the second 12 driver of the delay time contains information about the presence of a phase shift between the recorded high-frequency voltage signals and zero-sequence current, close to 90 °.

At the same time, the low-frequency channel 3 of the zero sequence voltage operates. The rectified input voltage from the output of the half-wave rectifier 22 passes through the first 23 low-pass filter, which extracts a useful component from the input signal that carries information about the amplitude of the low-frequency component of the zero-sequence voltage. Next, the signal is supplied to the threshold element 24 with a controlled threshold.

The control circuit 10 of the low-frequency channel of the zero-voltage voltage performs sequential control of the threshold value of the threshold element 24 of channel 3. In this case, the response threshold is set based on the following: as the maximum permissible value of the amplitude of the low-frequency component, the maximum short-term neutral bias level acceptable for the distribution network is taken, and in as the lower controlled value of the amplitude of the low-frequency component take acceptable For a distribution network, a continuous maximum level of neutral offset.

The control circuit 10 of the low-frequency channel 3 voltage zero sequence and the threshold element 24 with a controlled threshold act as follows. After turning on the power and setting the device to its initial state, the following voltage levels are established on the elements and outputs of the control system: at the first input 20 (low-frequency channel output 3) - “1”, at the input of counting cancellation of the fifth 28 shaper - “1”, at the input of the reference resolution the fifth shaper 28 is “0”, the output of the fifth 28 shaper is “0”, the output of the delay line 30 is “0”, the output 17 of the blocking signal is “0”, the control output 21 is “0”, the output of the second Low-pass filter 29 - "0", at the output 18 - "0". The threshold element 24 has a lower response threshold corresponding to the long-term maximum neutral displacement acceptable for the distribution network. In this case, the resistor 38 sets the operating point of the transistor 37, the control key 41 is closed, the zener diode 39 is connected to the base of the transistor 37.

If the amplitude of the low-frequency component of the voltage exceeds the zero sequence voltage of the lower monitored value, the lower threshold of the controlled threshold element 24 is triggered. In this case, the fifth 28 delay time former and the third 31 D-trigger are triggered. As a result, the SU 10 issues a control signal (output 21) to the LF channel 3 to set the upper threshold for the operation of the pore element 24, which corresponds to the maximum short-term level of neutral bias acceptable for the distribution network, and switches the threshold for a short time. In this case, the control key 41 is closed, the zener diodes 39 and 40 are connected to the base of the transistor.

The duration of the time interval during which the upper threshold is maintained at the threshold element 24 is set corresponding to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value. According to statistics, this time is on average 3 ms.

At the same time, the following voltage levels are set on the elements and outputs of the control system 10: at the first input 20 (the output of the LF channel 3) - “0”, at the input of cancellation of the fifth 28 shaper - “0”, at the input of the resolution of the fifth 28 shaper - “1 ", At the output 28 of the fifth shaper -" 1 ", at the output of the delay line -" 0 ", at the output 17 of the blocking signal -" 0 ", at the control output 21 -" 1 ", at the output of the second 30 low-pass filter -" 0 ", at the exit 18 - "0".

At the input of the cancellation of the counting of the fourth 14 of the shaper, a single signal is installed from the output of the low-frequency channel 3, which prohibits the operation of the shaper 14.

After increasing the response threshold, the output of the threshold element 24 returns to its initial state in a time much shorter than the pulse duration (less than 0.3 ms), which passes the second low-pass filter 29. As a result, when the response threshold is switched from lower to upper, the second low-pass filter prohibits the AND element 33 (output 18) to generate a signal to start the fourth 14 shaper.

At the input of the counting cancellation of the fourth 14 shaper, a zero signal is set from the output of the low-frequency channel 3, which allows the fourth 14 shaper to operate, i.e. fourth 14 shaper activated.

In the control circuit 10, the fifth 28 shaper enters the active state and generates at its output “1” for the delay line 30, which delays the signal by 3 ms. The device starts monitoring the change in the amplitude of the low-frequency component of the voltage of the zero sequence of channel 3 for 3 ms (control interval), which is set by the delay line 30. In the case of fixing during this time interval the excess of the low-frequency component of the maximum short-term level of neutral bias acceptable for the distribution network , element And 33 gives a signal to start the fourth 14 of the shaper (output 18), which is fed to its reference resolution input. For the damaged network at this moment in time, the signal from the output of the second 12 shaper is installed on the information input of the fourth 14 shaper, which contains information that the phase angle between the VPS 3i ₀ and VPS 3u ₀ is within the specified limits (close to or equal to 90 ° ) In this case, the fourth 14 shaper generates at its output an active signal containing information about the presence of OZZ. At the same time, the signal from the output of the fourth 14 shaper enters the input 19 of the control system and, through the third element, OR 34, enters the cancellation input of the third 31 D-flip-flop, and resets it to its original state. As a result, the threshold element 24 again sets the lower threshold. The same signal from the output of the fourth 14 shaper generates a blocking signal for the phase-sensing element, which is important for intact connection, as it prevents the device from platoon interference signal.

In the event of a damaged connection, the following voltage levels are established at the elements and outputs of the SU 10: at the first input 20 (the output of the low-frequency channel 3) - “0”, at the input of the countdown of the fifth shaper - “0”, at the input of the resolution of the fifth shaper and the output - “1”, at the output of the fifth driver - “1”, at the output of the second delay line - “0”, at the output 17 of the blocking signal - “1”, at the control output 21 - “0”, at the output of the second low-pass filter 29 - “1 ", At the exit 18 -" 1 ".

At this time, since the SU 10 is set to its initial state, the lower threshold of the threshold element 24 is set in the LF channel 3 and the further actuation of the threshold element 24 occurs from each half-wave of the low-frequency component of the zero-sequence voltage signal for the duration of the transition process until its amplitude exceeds the lower controlled level. As a result, the output of channel 3 receives the signals of the prohibition of counting the time to the inputs of canceling the counting of the fourth 14 and fifth 28 shapers of the delay time for a time, which is determined by the time of restoration of the normal operation of the network from the moment of the last operation of the threshold element 24. After the end of the transient process in channel 3, the shaper 14 starts the countdown and after the counted-down delay time, a zero signal is set at its output. As a result, at the output of the fourth shaper, the signal about the presence of an OZZ is stored during the transient time in channel 3 plus the delay time of the shaper 14 itself. Since the delay time of the second shaper (1.5 s) is average, selected taking into account the lifetime of high-frequency transients during single-phase earth fault, taking into account the time required to compensate for capacitive currents with a single-phase earth fault, taking into account the time that allows you to tune out interference signals and self tranyayuschihsya single-phase ground fault, the delay time of the fourth and fifth formers are selected such that the sum over time of the transition process in the LF channel 3 at nesamolikvidiruyuschihsya PTG it does not exceed 1.5 s. In the example embodiment of the device this time may be, for example, 0.6 s.

If there is an active signal at the second input of the SFD 16 from the output of the fourth shaper 14 after the delay time (5 ms) of the first 11 shaper, the SFD 16 stores a zero signal at its output and the second driver 12 continues the countdown.

After the delay time of the second 12 shaper expires and if there is an active “1” level from the output of the fourth 14 shaper at the information input of the third shaper at that moment of time, the latter is triggered by a signal from the inverse output of the second 12 shaper. A single level from the output of the third 13 shaper additionally blocks the phase-sensitive element 4 and activates the alarm generating circuit 9, the output of which is the output of the device. The device generates an alarm.

In the case when the phase angle between the VPS 3i ₀ and VPS 3u ₀ is not fixed within the specified limits (close to or equal to 90 °), the second 12 shaper has a passive “0” level at the information input of the fourth 14 shaper, which is a sign that the connection is not damaged. In this case, the passive “0” level is also set at the output of the fourth shaper 14, even though the amplitude of the low frequency component exceeds the zero voltage component of the zero sequence short-term maximum value. In this situation, the control signal at the output 21 of the control system, at which the upper threshold of the threshold element 24 is set, lasts 3 ms, since the signal at the input of the countdown of the third 31 D-trigger appears from the output of the delay line 30. The third 31 D-trigger is reset to the original state after 3 ms, after which the threshold threshold is set at threshold element 24, at the same time (after 3 ms), a blocking signal for the phase-sensitive element 4 appears at the output 17 of the control system 4. At the elements and outputs of the control system 10, the following voltage levels: at the first input 20 (LF channel 3 output) - “0”, at the input of cancellation of the fifth 28 shaper - “0”, at the input of the resolution of the fifth 28 shaper - “1”, at the output of the fifth 28 shaper - “1 ", At the output of the delay line 30 after 3 ms -" 1 ", at the output 17 of the blocking signal -" 1 ", at the control output 21 -" 0 ", at the output of the second low-pass filter 29 -" 1 ", at the output 18 -" 0 ".

At the output of the fourth shaper 14, a passive “0” level is also set if the amplitude of the low-frequency component does not exceed the maximum short-term neutral displacement level acceptable for the distribution network, despite the presence of the fourth 14 shaper of the active level from the output of the second 12 shaper.

In both cases, in the absence of an SCR at the second input of the SFD 16, a passive "0" signal is established from the output of the fourth 14 driver, which is fed to the first input of the OR-NOT 36 element in the SFD 16. At the first input of the SFD 16 (input of the short-pulse generator 35), as shown above, the signal is set from the output of the first 11 shaper. As a result, after the delay time of the first 11 shaper, which is chosen to be somewhat longer than the control time interval (approximately 5 ms) to implement the device’s operability, the short pulse shaper 35 generates a zero level from the first 11 shaper by the signal cut, which is fed to the second input of the OR element -NOT 36, at the output of which a signal for canceling the countdown of the second 12 shaper is formed and resets it. In this case, the device does not generate an alarm.

The device does not generate an alarm even in the case of self-liquidating OZZ, since in this case the transition process in channel 3 stops much earlier than with non-self-liquidating OZZ, and the fourth former also starts the countdown. As a result, a single signal from the output of the shaper 14 is replaced by zero before the end of the countdown time (1.5 s) of the shaper 12. The presence of a passive “0” level from the output of the fourth 14 shaper at the information input of the third shaper prohibits its start by the signal from the inverse output of the second 12 shaper and the device does not generate an alarm.

Claims (6)

1. A method of directional protection against a single-phase earth fault in an alternating current electrical distribution network, according to which, when a single-phase earth fault occurs, a low-frequency component corresponding to the operating frequency is isolated from a voltage signal of zero sequence, in addition, high-frequency components are isolated from current and voltage signals zero sequence, measure the amplitudes of their first half-waves, compare the measurement results with the corresponding reference values and, if available simultaneous excess over the reference values, measure the phase relationship between the signals of the high-frequency components of the current and voltage of the zero sequence at the moment of passage of the high-frequency current through zero, in addition, measure the amplitude of the selected low-frequency component of the voltage of the zero sequence, compare the obtained value with the reference, record the result, and at finding the phase angle within the specified limits and the presence of exceeding the reference value by the amplitude of the low-frequency component zero-sequence voltages generate an alarm signal after a time interval that is set taking into account the lifetime of high-frequency transients during a single-phase earth fault and taking into account the time required to compensate for capacitive currents during a single-phase earth fault, characterized in that as a reference value for the amplitude the low-frequency component of the voltage zero sequence take the maximum allowable and lower controlled value of the amplitude, while e of the maximum permissible value of the amplitude of the low-frequency component, take the maximum short-term neutral displacement acceptable for the distribution network, and the longest maximum neutral displacement, acceptable for the distribution network, which is acceptable for the distribution network, is taken as the lower control value of the amplitude of the low-frequency component, if, as a result of measuring the phase relations between the high-frequency signals components of current and voltage of the zero sequence at the time of passage after a high-frequency current zero, the phase angle is within the specified limits, then the result of the phase angle measurement is fixed during the control time interval, the duration of which is set according to the time during which, when a single-phase earth fault occurs, the neutral voltage reaches the maximum permissible value, after why during the control time interval the amplitude of the extracted low-frequency component of the voltage of the zero sequence is measured, for which first The presence of an excess of the low-frequency component of the voltage of the zero-sequence voltage of the zero sequence of the lower monitored value is checked, and, if the excess of the lower monitored value is recorded, the presence of the excess of the maximum permissible value by the amplitude of the low-frequency component of the voltage of the zero sequence is monitored, if the fact of exceeding the maximum permissible value is recorded, then an alarm is generated after the moment of fixation after a time interval, cat The second one is also set, taking into account the time, allowing to tune out interference signals and self-eliminating single-phase earth faults. 2. A device for implementing a method of directional protection against a single-phase earth fault in an alternating current distribution electric network, comprising high-frequency channels of current and zero sequence voltage, the inputs of which are respectively the input of the zero-sequence current signal and the input of the zero-sequence voltage signal, while the high-frequency channels are made identically; a low-frequency voltage channel of the zero sequence, the input of which is connected to the input of the voltage signal of the zero sequence, a phase-sensitive element, the inputs of which are connected from the first to the fourth, respectively, the outputs of the positive and negative polarity of the first half wave of the high-frequency signals of the current channels and voltage of the zero sequence, and the alarm generating circuit, the output of which is the output of the device, characterized in that the low-frequency control circuit is additionally introduced the neutral voltage channel (CS), the first to fourth delay time drivers, the first OR element, the phase detection result reset circuit (SFD), while the control block signal output and the shapers outputs are connected to the inputs of the first OR element, the output of which is connected to the phase-sensitive element blocking input, the information inputs of the first delay time driver are connected to the outputs of the high-frequency channel of the zero-sequence current, and the output is connected to its own an operation blocking ode to the first input of the SFD, the output of which is connected to the counting cancellation input of the second delay time driver, the input of which is connected to the output of the phase-sensitive element, and the output, in addition, is connected to the information input of the fourth delay time driver, while the inverse output of the second driver connected to the input resolution permission of the third shaper, the information input of which is connected to the output of the fourth shaper and to the second input of the SFD, while the input permission the accounts of the fourth driver and the output are connected respectively to the output and the second input of the control system, the first input of which and the cancellation input of the fourth driver are connected to the output of the low-frequency channel of zero sequence voltage, the control input of which is connected to the control output of the control system, in addition, the output of the third driver is connected to the input alarm generation circuits, while the low-frequency channel of the zero-sequence voltage contains two-half-wave connected in series a rectifier, a first low-pass filter and a threshold element with galvanic isolation and a controlled threshold, while the input of the rectifier is the input of the low-frequency channel, the output and control input of the threshold element, respectively, the output and control input of the channel. 3. The device according to claim 2, characterized in that the phase-sensitive element contains the first and second D-flip-flops and the second OR element, the inputs of which are connected to the outputs of the triggers, and the output is the output of the phase-sensitive element, while the C and D inputs of the first trigger are connected with outputs of positive polarity of the first half-wave of high-frequency signals of current channels and zero-sequence voltage, and C and D inputs of the second trigger are connected to outputs of negative polarity of the first half-wave of high-frequency signals of current channels and voltage zero sequence, respectively, while the R-inputs of the triggers are connected and are the input lock phase-sensitive element. 4. The device according to claim 2, characterized in that the control circuit of the low frequency voltage channel of the zero sequence voltage comprises a fifth delay driver, a second low-pass filter, a delay line, a third D-trigger, an element NOT, an AND element, and a third OR element, and the input of the element is NOT the first input of the control system and is connected to the input of the countdown of the fifth driver, in addition, the output of the element is NOT connected to the input of the second low-pass filter and to the inputs of the resolution of the third D-trigger and the fifth driver; for which it is connected to the input of the delay line, the output of which is connected to the first input of the third OR element, the second input of which is the second input of the control unit, and the output is the output of the blocking signal of the control unit, in addition, the information input of the fifth driver is connected to the signal source of a single level, and the output the third OR element is connected, in addition, to the cancellation input of the third D-flip-flop, the information input of which is connected to the signal source of the unit level, and the output is the control output of the control system and, in addition, It is connected to the first input of the And element, the second input of which is connected to the output of the second low-pass filter, and the output is the output of the control system. 5. The device according to claim 2, characterized in that the phase detection result reset circuit (SFD) comprises a short pulse shaper and an OR-NOT element, wherein the input of a short pulse shaper is the first input of the SFD, the first input of the OR-NOT element is the second input of the SFD , the second input of the OR-NOT element is connected to the output of the shaper of short pulses, and the output of the OR-NOT element is the output of the SFD. 6. The device according to claim 2, characterized in that in the low-frequency channel of the zero sequence voltage, the threshold element with a controlled response threshold contains an npn transistor, in which a resistor is connected in parallel with the base-collector junction, and the first zener diode is connected in series to the base, to which a second zener diode is connected, in parallel with which a control key is connected, the opening contact of which is connected to the control input of the low-frequency channel, and the minus of the second zener diode is connected to the low-frequency output anal.

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