RU2156531C1 - Device for detection f phase ground short circuit in three-phase power supply network with insulated neutral wire - Google Patents

Abstract

FIELD: protection equipment for electrical engineering. SUBSTANCE: device has serial circuit of zero sequence voltage detector, industrial frequency filter, voltage stepping up circuit and clock oscillator. Goal of invention is achieved by generator of clock pulses displaced by half period. Said generator is introduced into said circuit. In addition, each phase of power supply network has serial circuit of feeding phase voltage detector, reference pulse generator, synchronous D flip-flop, AND gate. Goal of invention is achieved by following members introduced into phase circuits: serial circuit of generator of clock pulses displaced by half period, and second synchronous D flip-flop are introduced between output of feeding phase voltage detector and second input of AND gate. Device provides separate detection of short circuited phases. Both results are updated for one complete period of zero sequence with relative displacement of half period. This results in possibility to double frequency of result production. EFFECT: increased stability to errors in detection of short circuited phase without time losses for validity check. 2 cl, 2 dwg

Description

 The invention relates to the field of electrical engineering, in particular electrical safety, and is intended to protect against electric shock and other dangerous consequences of current leakage to earth by determining and subsequent protective shunting of the damaged phase of the network to earth. The invention is designed primarily for use in underground three-phase electrical networks with an isolated neutral voltage of up to 1140 V.

 In known devices for determining the damaged phase to earth, both phase and amplitude parameters of the vibrational signals are used. The use of phase parameters provides higher accuracy of signal processing, since useful information is extracted with respect to their zero transitions, which prevents the occurrence of recognition errors of small changes in amplitude parameters for a limited time from electrical safety conditions.

A device is known for determining a damaged phase of a network, comprising a zero sequence voltage sensor, a line voltage sensor, a phase difference sensor between a zero sequence voltage and a line voltage, a threshold signal splitter that implements the task of defining a reference phase gap of 90 ^° for each phase of the network and determining a damaged phase network - fixing the network phase as damaged by detecting compliance with one of the reference phase gaps of the initial phase of the zero voltage phase sequence (said phase difference) [1].

The device has a low sensitivity to leaks due to the limitation of the reference phase gaps of 90 ^o . The real value of the area of change of the initial phase of the zero-sequence voltage during single-phase dangerous leaks in the network can exceed 90 ^o under the influence of the natural asymmetry of the insulation resistances in the phases of the network. This is especially evident in high-resistance leaks - leaks with a resistance close to the asymmetric insulation resistance. As a result, the values of the specified initial phase go beyond the reference phase gap, the damaged phase of the network is not fixed. To increase the sensitivity to leaks, the expansion of the reference phase gaps is required. Another disadvantage of the device is the need to observe the phase sequence when connected to the network, since all three reference phase gaps are counted relative to one line voltage.

Closest to the proposed device for determining the damaged phase to earth in a three-phase network with an isolated neutral contains a zero-sequence voltage sensor (in the form of a zero-sequence voltage filter formed by the primary windings of a three-phase transformer connected by a star and connected to the network phases), an industrial frequency filter (in the form of a zero sequence voltage measuring unit, which distinguishes a component of the industrial frequency), the control unit for increasing the voltage is ia (in the form of a series-connected amplitude selector and delay element), a pulse shaper (converting the voltage of the zero sequence of industrial frequency into short pulses) and for each phase of the network a sensor of the supplying phase voltage (in the form of a secondary winding of a three-phase transformer), a reference pulse shaper (converting supply phase voltage in pulses, called the original information with a duration corresponding to the phase interval to 120 ^o minus phase Prome a clock pulse), a D-flip-flop and a logic element And, the output of the zero-sequence voltage sensor connected to the input of the industrial frequency filter, the output of which is connected to the input of the voltage increase control unit and the input of the clock generator, and for each phase of the network, the output of the supply phase sensor voltage is connected through the driver of the reference pulses to the information input of the D-trigger, the clock input of the D-trigger is connected to the output of the driver of the clock pulses, and the output is connected to the first input Skog AND gate, whose second input is connected to the output control unit increasing the voltage, and output - with the actuating body [2].

In this device, the correspondence between the reference phase gap of the initial phase of the voltage of the zero sequence of industrial frequency is controlled using a D-trigger that stores the value of the reference pulse when it coincides in time with the clock pulse. The reference phase gaps are counted relative to the supply phase voltages individually for each phase of the network. As a result of this, the result of determining the damaged phase is generated autonomously for each phase of the network and does not depend on the order of alternating phases of the network. The value of the reference phase gap in total with the clock can be assigned to any, but not more than 120 ^o - the boundaries of the unambiguous determination of the time-phase in a three-phase network. With a total value close to 120 ^o , the restriction on sensitivity to hazardous earth leaks is lifted, which is necessary to comply with electrical safety requirements. However, with increased sensitivity, the reliability of the device decreases due to the deterioration of stability against erroneous determination of the damaged phase during high-resistance hazardous leaks. As a result of the subsequent shunting of the “healthy” phase of the network to the ground, electrical safety conditions worsen. The deterioration of this stability is due to the forcedly small amount of delay introduced by the voltage increase control unit. By its output signal - a signal about the appearance of a dangerous leak to the ground, the damaged phase of the network is recorded. Thus, the delay in the operation of the voltage increase control unit is the main means of ensuring stability in the device. The delay value is limited by electrical safety conditions and is calculated on the basis of the permissible time of existence in the network (before protective bypass) of the current through the person (with minimal resistance) minus the response time of the actuators. For networks with a voltage of 1140 V, the delay value can be allowed up to two periods of oscillation of the industrial frequency. With a higher mains voltage, the delay, of course, should be less. The appearance of high-resistance single-phase hazardous leaks may be accompanied by a transient with a duration exceeding the specified delay value. Such a transient process, together with other non-industrial frequency noise, can “drive” the clock pulse beyond the boundaries of the reference pulse related to the damaged phase of the network. As a result, the adjacent phase of the network is erroneously defined as damaged. Improving the reliability of the device is possible by checking the result of determining the damaged phase for reliability. However, simply duplicating the result for the purpose of such verification is unacceptable due to the additional time costs that are not acceptable when determining the damaged phase of the network with the low resistance, most dangerous leakage to earth.

 The basis of the invention is the task of increasing the reliability of the device for determining the damaged phase to earth in a three-phase network with isolated neutral by checking the reliability of the result of determining the damaged phase without additional time costs by increasing the frequency of obtaining the result from one to two times for a complete voltage fluctuation of the zero sequence. The use of the invention will provide stability against erroneous determination of the damaged phase of the network without loss of speed with the most dangerous earth leaks.

To this end, to a device for determining a damaged phase to earth in an isolated neutral network, containing a zero-sequence voltage sensor, an industrial frequency filter, a voltage increase control unit, a clock driver and, for each phase of the network, a supply phase voltage sensor, a reference pulse generator, D -trigger and logic element AND, and the output of the zero-sequence voltage sensor is connected to the input of the industrial frequency filter, the output of which is connected to the input of the control unit the role of voltage increase and the input of the clock driver, and for each phase of the network the output of the supply phase voltage sensor is connected through the driver of the reference pulses to the information input of the D-trigger, the clock input of the D-trigger is connected to the output of the driver of the pulse pulses, and the output is connected to the first input of the logic aND gate whose output is connected to the actuating body additionally introduced offset generator 180 ^o clock, and for each network phase offset generator 180 ^o reference pulse c and the second D-trigger, all D-triggers being synchronous and with a reset input, the output of the voltage increase control unit is connected to the reset inputs of all D-triggers, the output of the voltage increase control unit or reset input for all D-triggers is inverse, the input a shaper of 180 ^° clock-shifted clock pulses is connected to the output of the industrial frequency filter or an output of a clock shaper, and for each phase of the network, the output of the supply phase voltage sensor is connected through a shaper of a 180 ^° shift pulses with the information input of the second D-trigger, the clock input of which is connected to the output of the shaper of clock pulses offset by 180 ^o , and the output to the second input of the logic element I.

 These distinctive essential features are sufficient in all cases to which the scope of legal protection of the invention applies. The following are the distinguishing features characterizing the invention in a particular case.

An embodiment of a clock shaper in the form of a null-comparator is proposed, and a shaper of clock pulses offset by 180 ^° in the form of a logic element NOT, the input of which is connected to the output of a null-comparator.

A new technical property of the invention is achieved as follows. Introduced into the device a new (distinct) characteristics: offset generator 180 ^o clock pulses and for each network phase generator 180 ^o spaced reference pulses and a second D-flip-flop in conjunction provide a second (additional) the determination result of the damaged phase network. Obtaining the first result provides known features of the device. The alternation of both results in time is random. Both results are updated once for the complete voltage fluctuation of the zero sequence, but with a relative offset of 180 ^o , corresponding to half the full fluctuation. As a result, the result of determining the damaged phase is obtained twice for the complete voltage fluctuation of the zero sequence. The logical element And for each phase of the network forms the final result of determining the damaged phase with a check for reliability - by the coincidence of the active states of the first and second D-flip-flops (the first and second results of determining the damaged phase). At the same time, the time spent on determining the damaged phase remains the same as in the case of determining the damaged phase without checking the result for reliability. The appearance of a dangerous earth leak in the network is a command indicating the need to determine the damaged phase, and for the device corresponds to the permission of the D-triggers. For this purpose, the reset inputs of D-flip-flops are used, to which the enable signal comes from the output of the voltage increase control unit. Due to the validation check, stability is achieved against erroneous determination of the damaged phase, which increases the reliability of the device.

 The purpose of the distinguishing features characterizing the invention in a particular case is as follows.

The implementation of D-triggers synchronous makes it possible to easily implement clock shapers and 180 ^{o off-} clock pulses, respectively, in the form of a zero comparator and NOT logic element, which also increases the reliability of the device. In this case, the property of switching the synchronous D-flip-flop along the signal front at the clock input is used.

 In FIG. 1 shows a functional diagram of the device, FIG. 2 is a timing chart explaining the operation of the device in case of damage in the phase A network.

The functional diagram of the device contains a zero-sequence voltage sensor 1, supply phase voltage sensors 2, an industrial frequency filter 3, a clock shaper 4, a shaper of 180 clock pulses offset by 180 ^o , a voltage increase control unit 6, and then, according to the number of network phases, reference pulse shapers 7 , shapers of reference pulses 8 offset by 180 ^o , first and second synchronous D-flip-flops 9 and 10, as well as logic elements And 11. The diagram also shows:
A, B, C - network phases;
U ₀ - voltage zero sequence;
u ₀ - the output signal of the filter 3, proportional to the voltage U ₀ industrial frequency;
u _A , u _B , u _C - output signals of sensors 2, proportional to the supply phase voltage of the network;
a ₁ , b ₁ , c ₁ - the first reference pulses at the outputs of the shapers 7 for phases A, B, C;
a ₂ , b ₂ , c ₂ - second, offset by 180 ^o reference pulses at the outputs of the shapers 8 for phases A, B, C;
z ₁ , z ₂ - the first clock pulses and the second, 180 ^o offset clock pulses at the outputs of the shaper 4 and 5, respectively;
r is the signal from the inverse output of the control unit for increasing voltage 6 (signal reset D-flip-flops to zero);
Q ₁ ^A , Q ₂ ^A - output signals of the first and second D-flip-flops 9 and 10 in the damaged phase A.

The time chart additionally shows:
T is the period of oscillation of the industrial frequency;
τ is the time shift of the first reference pulses a ₁ , b ₁ , c ₁ relative to the zero transitions of signals u _A , u _B , u _C ;
τ _o is the deceleration time of the industrial frequency filter 3;
Δt is the delay time of the final result of determining the damaged phase relative to the moment of occurrence of a signal about the occurrence of a dangerous leak to the ground;
t is time.

 The operation of the device is as follows.

According to the signals u _A , u _B and u _C from the outputs of the sensors 2 of the supply phase voltage of the network (made, for example, in the form of secondary windings of a three-phase transformer, the primary windings of which are connected by a star and connected to the phases of the network), the generators 7 (Fig. 1) generate the first reference pulses a ₁ , b ₁ , c _{1 of a} given duration equal to a third of the period T and the corresponding value of 120 ^{o the} reference phase gap. The first reference pulses (phase gaps) a ₁ , b ₁ , c ₁ are shifted (Fig. 2) relative to the zero transitions of the signals u _A , u _B , u _C from negative to positive values by a fixed interval τ (phase shift ωτ, where ω is the circular frequency of the network), due to the implementation of the shapers 7. So, in the case of the implementation of the shapers 7 in the form of comparators, when the instantaneous values of the input signals exceed a threshold equal to half the maximum value of these signals, the interval τ is T / 12 (phase shift ωτ = 30 ^o ). This case corresponds to the time diagram. In another implementation, for example in the form of single-vibrators, the interval τ can be any fixed value within the period.

Shapers 8 generate from the signals u _A , u _B , u _{C the} second reference pulses a ₂ , b ₂ , c ₂ offset from the first reference pulses a ₁ , b ₁ , c ₁ by a half period T / 2 (180 ^o ). Shapers 8 can be implemented, for example, in the form of comparators operating when the instantaneous values of the input signals decrease below a threshold equal to half the minimum value of these signals (as shown in the time diagram).

Damage to the insulation in the network in the form of a leak in phase A causes the appearance of voltage U _{0 of the} zero sequence. This voltage is allocated by the sensor 1, made, for example, in the form of a zero-sequence voltage filter formed by the primary windings of a three-phase transformer. In the general case, voltage U ₀ contains a useful (informational) component of industrial frequency and interference — components of non-industrial frequency, for example, created by the operation of a device for monitoring the active insulation resistance of a network. The industrial component of the voltage U _{0 is} shifted relative to the signal u _A by the phase angle determined by the transfer properties of the zero sequence circuit of the network. In FIG. Figure 2 shows the oscillations U _{0 of the} industrial frequency for the boundary values of the phase shift in the absence of leaks in the adjacent phases of the network: - 90 ^o and 0 ^o . Filter 3 selects a useful signal u ₀ proportional to the voltage U _{0 of the} industrial frequency, and at the same time slows it down by a time τ _o to bring the average value of the initial phase of the signal u ₀ into correspondence with the middle of the reference phase gap related to phase A. This deceleration neutralizes the fixed shift τ introduced by the shapers 7 and 8, and correctly orientates the zero transitions of the signal u ₀ relative to the reference pulses. Then, from the signal u ₀ , the first clock pulses z ₁ and the second clock pulses z ₂ offset from them by 180 ^{o are} formed by the shaper 4 and 5, respectively. The clock pulses shown in the time diagram in the form of a meander correspond to a variant of the simple implementation of the shapers 4 and 5 in the form of zero comparator and logical element are NOT, respectively. Shapers 4 and 5 can also generate clock pulses in a form different from the meander. Moreover, for the implementation of the shaper 5 it may be more convenient to connect its input to the output of the filter 3 (in the diagram, this connection is shown by a dashed line).

The damaged phase of the network is determined by the coincidence of the two results. One result is determined for each phase of the network by detecting the correspondence of the first reference phase gap to the phase shift between the supply phase voltage and the signal u ₀ , i.e., the coincidence in time of the first reference pulse (one of the pulses a ₁ , b ₁ , c ₁ ) and the edge the first clock pulse z ₁ . Another result is also determined for each phase of the network by detecting the correspondence of the second reference phase gap to the phase shift between the supply phase voltage and the inverse signal u ₀ , i.e., by the coincidence in time of the second reference pulse (one of the pulses a ₂ , b ₂ , c ₂ ) and the front of the second clock pulse z ₂ . The indicated coincidences in time are recorded respectively by the first and second synchronous D-flip-flops - 9 and 10. The inclusion of all D-flip-flops is carried out with the appearance of a dangerous earth leak, recognized by block 6 by increasing the output signal u _{0 of} filter 3. To turn on D -triggers, reset inputs (R-inputs) are used, to which a logic signal r of low (zero) level, which works, is supplied from the inverse output of block 6, as shown in the device diagram (in the case of using D-triggers with an inverse reset input, bl 6 to operate with a noninverted output). At the moment of arrival of the permission signal r = 0, the triggers are in the zero (inactive) state, characterized by a low level of output signals. According to the positive differences of pulses at the clock inputs (C-inputs) of the triggers, the latter take a state corresponding to the values of the reference pulses at the information D-inputs. With a damaged phase A, the positive changes in the clock pulses z ₁ and z ₂ occur during the action of the reference pulses a ₁ and a _2, respectively. According to the positive differences of clock pulses, D-flip-flops 9 and 10, related to phase A, go into the active state, characterized by a high (single) level of output logic signals at the outputs: Q ₁ ^A = Q ₂ ^A = 1. A single value of only one signal Q ₁ ^A or Q ₂ ^A is, in time, the first (preliminary) result of determining the damaged phase A. The final result of determining the damaged phase is generated with the appearance of a single value of the second signal that repeats the first and thereby confirms its reliability. The coincidence in time of the single signals Q ₁ ^A and Q ₂ ^{A is} detected by the corresponding logical element And 11, the output signal of which controls the operation of the executive body, for example, a device for protective shunting of the damaged phase to earth.

In subsequent clock cycles of signals z ₁ and z _{2, a} single state of the indicated D-flip-flops will be confirmed until the damage is repaired; and the appearance of the reset signal r = 1. Triggers related to the “healthy” (intact) phases of the network have been inactive all this time.

The delay in the appearance of the result of determining the damaged phase relative to the moments of recognition of the occurrence of a dangerous earth leakage in the network (signal r goes from high to low) is from half to the full fluctuation of the signal u ₀ due to the randomness of the moments of occurrence of the output signal of block 6 and is caused by the delay Δt of the transition to the unit value of the second, confirming signal. On the time diagram with such a delay, a single value of the signal Q ₁ ^A appears. The delay equal to the "duration of the full oscillation of the signal u ₀ is the maximum for the device that determines the damaged phase of the network without checking for reliability. In comparison with it, in the proposed device for the same time, the result of determining the damaged phase is formed with a check for reliability, which ensures stability against erroneous determination of the damaged phase.

Due to the validation check, the speed limits of the control unit 6 for increasing the voltage u ₀ are additionally removed without the risk of erroneously determining the damaged phase. In this case, the response delay of block 6 can be reduced to the minimum value necessary mainly to ensure stability against impulse noise. In addition, a delay of both a fixed and a variable value is allowed, which expands the possibilities of implementing block 6. So, in the case of monitoring the increase in voltage u ₀ by its instantaneous value, it is convenient to use a fixed delay in block 6. In the case of monitoring the increase in voltage u ₀ according to its measured average straightened or actual value, the response delay of block 6 is caused by the inertia of the corresponding meter and is a variable in the form of a decreasing function of the voltage u ₀ .

The above description of the operation of the device relates to the case of the appearance of a low-resistance, most dangerous leak in the network, accompanied by a short-term transient process of establishing the voltage U ₀ , which contributes to the rapid determination of the damaged phase of the network.

In the case of the appearance of a high-resistance dangerous leakage in the network, accompanied by a long transient process of establishing the voltage U ₀ , the time to determine the damaged phase of the network will be determined by the transient decay time until a reliable result occurs. Electrical safety conditions are also observed due to the lower value of the leakage current.

List of sources
1. A.S. USSR N 1379857, H 02 H 3/16, publ. in B.I. 1988, N 9.

 2. A.S. USSR N 943959, H 02 H 3/16, publ. in B.I. 1982, N 26.

Claims (2)

1. A device for determining the damaged phase to earth in a three-phase network with an isolated neutral, containing a zero-sequence voltage sensor, an industrial frequency filter, a voltage increase control unit, a clock driver and, for each phase of the network, a supply phase voltage sensor, a reference pulse generator, D- a trigger and a logical element And, and the output of the zero-sequence voltage sensor is connected to the input of the industrial frequency filter, the input of which is connected to the input of the control unit To increase the voltage and the input of the clock driver, and for each phase of the network, the output of the supply phase voltage sensor is connected through the driver of the reference pulses to the information input of the D-trigger, the clock input of the D-trigger is connected to the output of the driver of the pulse pulses, and the output is connected to the first input of the logic aND gate whose output is connected to the actuating body, characterized in that it introduced shaper 180 ^o displaced clock pulses, and for each network phase offset generator supports 180 ^o of pulses and a second D-trigger, all D-triggers being synchronous and with a reset input, the output of the voltage increase control unit is connected to the reset inputs of all D-triggers, the output of the voltage increase control unit or the reset input for all D-triggers is inverse, the input of the shaper of clock pulses offset by 180 ^{o is} connected to the output of the industrial frequency filter or the output of the shaper of clock pulses, and for each phase of the network the output of the sensor for the supply phase voltage is connected through the shaper 180 ^o reference pulses with the information input of the second D-flip-flop, the clock input of which is connected to the output of the shaper of 180 ^o offset clock pulses, and the output to the second input of the logic element I. 2. The device according to claim 1, characterized in that the clock shaper is made in the form of a null-comparator, and the shaper of clock pulses offset by 180 ^o is in the form of a logical element NOT, the input of which is connected to the output of the null-comparator.

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