EP3186867A1

EP3186867A1 - Method and device for automatic tuning a continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system

Info

Publication number: EP3186867A1
Application number: EP15763483.3A
Authority: EP
Inventors: Ivan Matuljak; Petr VANCATA
Original assignee: Ege spol sro
Current assignee: Ege spol sro
Priority date: 2014-08-28
Filing date: 2015-08-26
Publication date: 2017-07-05

Abstract

A method for automatic setting an arc suppression coil (9) using an auxiliary signal (14) supplied to the point of zero-sequence component of an electrical system (10). The auxiliary signal (14) is formed by a current or voltage with variable angular frequency and is used for determining the resonant angular frequency ω_rez of the actual state of the electrical system (10) which is compared with the fundamental angular frequency ω_s of the system (10). The arc suppression coil (9) is then tuned towards the desired resonant state L_Srez. The auxiliary signal (14) used for tuning the arc suppression coil (9) may also comprise at least one pair of complementary frequency components with the same size amplitude, the angular frequency ω_i, ω_ii of which is selected so that the value of the response of the electrical system (10) to the auxiliary signal (14 ) is, for both of these complementary angular frequencies ω_i, ω_ii, equally large at the very point of tuning, where the circuitry for the fundamental angular frequency ω_s reaches a resonance state. For tuning the arc suppression coil (9) there is utilized a device (13) including a generator (8) of the auxiliary signal connected to the neutral point of the system (10), an evaluation unit (11), and a control unit (12), wherein the device (13) is provided with hardware and a software module (15) for controlling the frequency of the auxiliary signal (14) and with an evaluation of response of the electrical system (10) for carrying out the method of automatic setting of the arc suppression coil (9) according to the invention.

Description

Method and device for automatic tuning a continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system

Field of the invention

The invention relates to the field of electrical engineering and power distribution, specifically to a method and device for automatic tuning of an arc suppression coil that compensates earth-fault currents that occur as the result of a fault between one phase of an electrical system and the ground potential.

Background of the invention

To compensate fault currents which occur at the site of an earth-fault of some phase of an electrical distribution system, also known as a "single-phase earth-fault" or "earth-fault", the basic compensation device used is a continuously and/or discretely tunable arc suppression coil, called the "Petersen coil" connected between the node of the system, also called the "zero point", "star point" or "neutral point of the system", usually consisting of a node of a power transformer, or of a "node of a special grounding transformer", and the ground potential. This arc suppression coil operates on the resonance principle when the inductive reactance of the arc suppression coil is set to the same value as the total capacitive reactance of the distribution system to the ground potential. In the occurrence of an earth-fault, the properly tuned arc suppression coil compensates the fault current.

The purpose of arc suppression coil tuning is to determine the overall capacitance of the network to the ground potential and to set the reactance of the suppression coil to a state of resonance with this capacitance. Arc suppression coil tuning is carried out according to known methods, which can be divided into two groups.

One group is made up of resonance methods in which the voltage of the neutral point of the network to the ground is monitored. The Neutral point voltage of the network is also called the "neutral voltage displacement (NVD)", or "zero-system voltage", or "voltage of the zero- sequence component". Neutral point voltage of a network is caused by the natural unbalance (non-symmetry) of the phase capacitances of a network to the ground potential. This voltage varies according to the state of detuning of the resonant circuit for the base frequency of the network and achieves its peak just at the point of achieved resonance. The tuning process according to resonance methods involves changing the reactance of the arc suppression coil and monitoring the caused change of the voltage of the network node. During each attempt to find the resonance state, it is thus necessary to change the settings of the arc suppression coil, even if the coil is tuned correctly and this condition is only necessary to be verified.

The second group of tuning methods are methods based on the use of an auxiliary signal transmitted to the network, usually directly to its neutral point, and monitoring and evaluating the response in the voltage of the network node against the earth-fault for the generated auxiliary signal. Methods based on the use of an auxiliary signal are described in the following patent documents.

According to document CZ 85552, a device is known for tuning of arc suppression coils. To control the wning, the device compares the vectors of the driving voltage and the voltage at the arc suppression coil, while for the tuning indicator a cathode ray tube is used on whose horizontal system of deflection plates there is supplied voltage from the driving transformer via the driving voltage divider, while on the vertical system there is supplied voltage from the measuring windings of the arc suppression coil via a regulation transformer or a tube amplifier.

The device described in document SU 860207 serves to stabilize the resonance state of the reactance of the arc suppression coil and the capacitive reactance of the distribution system. The device contains a sensor for the monitored parameter which is the voltage or current of the zero-sequence component, further a switching element for controlling the arc suppression coil, a low-frequency generator which is connected to the distribution system via a modulator and a bandpass type filter, two amplitude detectors, and a reference block. The operation of this device lies in the fact that the generator produces a periodic signal at a frequency Ω which is less than the frequency ω of the distribution system to the zero-sequence component of the distribution system, e.g. via the auxiliary winding of the arc suppression coil. The signal received by the sensor incorporates two harmonic components ω ± Ω. The amplitudes, respectively the absolute values of these components, are, using the bandpass type filters, fed into two amplitude detectors. These two signals carry information about the state of resonance of the arc suppression coil and the distribution system. The difference of amplitudes is carried out in the reference block. If the difference is zero, the arc suppression coil is tuned to the resonance with the distribution system.

Document EP 0 595 677 describes a known device and a method for tuning and detuning of compensation by injecting of an auxiliary signal to a circuit of a network node while measuring the changes of the zero voltage induced by the said injection of the auxiliary signal and measuring the amplitude and phase shift of the impedance by implementing a change of the zero voltage with the measuring auxiliary signal. The auxiliary signal is injected in series or parallel with the compensating arc suppression coil and can be injected through an auxiliary zero-sequence transformer. The device has the character of a current source that uses the auxiliary voltage of the appropriate network substation. The zero transformer contains a secondary winding which supplies, in the case of a direct ground fault in the network, a low voltage, and the power source further comprises a resistor of several tens of ohms which is connected to the auxiliary voltage in the substation. The generated current forms as a result of the connected auxiliary voltage of the substation across the reactance of an inductive character into the circuit of a network node and thus has the same frequency as the distribution system.

Document CZ 286 527 discloses a method of controlling a three-phase network to change the alignment of the grounding coil in which the voltage is measured continuously at the neutral point and compared with the tolerance range, and notifies the abandonment of the tolerance range of the change in alignment. The grounding coil is continuously acted upon by an auxiliary signal which causes an increase in voltage at the neutral point. The voltage at the neutral point is continuously compared with the lower threshold value, below which voltage changes at the neutral point can not be measured with sufficient sensitivity. When exceeding the threshold value, the ground coil is continuously acted upon by an auxiliary signal to cause an increase in voltage at the neutral point. For manual or automatic alignment of the grounding coil on a selected degree of compensation, in the event of change, the connected auxiliary signal is discretely or continuously changed in value and/or phase from which, using a comprehensive comparison of the change in voltage at the neutral point with the change of the auxiliary signal, the detuning of the grounding coil is determined. The grounding coil is set based on the detuning at the selected degree of compensation. The auxiliary signal changes by reversing its phase. The effect by the auxiliary signal on the grounding coil is made by direct connection of the auxiliary current to the ground point of the three-phase network or by connection to the auxiliary winding of the coil.

A method of selective identification and localization of high-ohm earth-faults in electric networks with compensated neutral point at which the center of the network is powered via at least one auxiliary signal with the network frequency is described in detail in document EP

1 307 753. Furthermore, this document describes the procedure for tuning the arc suppression coil in a network with a network frequency where at least one other auxiliary signal is

used with frequency which is different from the mains frequency. The auxiliary signal with frequency in the form of a current causes a zero-sequence voltage of the neutral point of the network with the same frequency ω; as the auxiliary signal has. The amplitude and phase of zero-sequence voltage and of the auxiliary current are continuously measured, from which the admittance and conductance of all ground branches of the network and the admittance and conductance of the arc suppression are determined. The auxiliary signal may include more frequency components, wherein for each frequency component cot the respective admittance and conductance are calculated. The current sizes of the various frequency components are selected so that the effective value of the zero-sequence voltage caused by them in the neutral point of the network is less than 10% of the effective value of the fundamental harmonic component of the phase voltage of the network. According to calculated and observed parameters, the regulator adjusts the arc suppression coil to the desirable compensation, undercompensation, or overcompensation and records the relevant parameters. The necessary auxiliary signal is formed in the signal generator. The generator generates a specific right- angle signal which is further treated by filtration in the low-frequency pass.

Document DE 103 07 668 describes a method for determining the parameters of the compensated network without detuning the arc suppression coil, consisting of a number of successive steps, wherein a current is first introduced to the zero-sequence system of a network, composed primarily of two components with generally varying amplitude and frequency. These frequency components in the network node voltage are measured for their size and angle. In the next steps, the admittances of the network are calculated for the two used frequencies, again as to their size and angle. The solution of the resulting system of complex equations serves to determine the individual parameters of the network, i.e. its total capacitance to the ground, inductance of the arc suppression coil, and the actual detuning of the resonant circuit. For the case in which the voltage of the zero-sequence component in the network is not measured in its node but in the terminals of the transformer, the procedure is described which takes into account the influence of the transformer inductance on the measured voltage, the result of which is also the establishment of the network capacitance, the inductance of the arc suppression coil, and the detuning of the circuit. Introducing a current of an auxiliary signal is carried out either to the node of the power transformer or to the "creator" of the artificial zero point of the network, either through an auxiliary transformer or through a power winding of an arc suppression coil. The new measurement cycle is caused by a change in the fundamental harmonic component of the voltage of the network node. The two used frequency components of the introduced auxiliary signal are selected so that their frequencies are near the resonant frequency of the network. This method allows the calculation and the division of unbalance in individual phases, wherein the size of the injected current is regulated upon achievement of the maximum change of voltage of the network node.

Known devices for automatic setting the continuously and/or discretely tunable arc suppression coils using an auxiliary signal connected to the neutral point of a network operate identically in principle, in the sense that they use the signal or signals of a given frequency equal to or different from the nominal frequency of the network, and measure and in a certain way evaluate the voltage response as for the corresponding frequency (frequencies) of the resonant circuit formed by the arc suppression coil and the capacitance of the network.

The disadvantage of the known devices and methods for automatic setting the continuously and/or discretely tunable arc suppression coil consists in the fact that the signals they monitor have a frequency the same or relatively close to the nominal frequency of the network, so that for states in which the resonant circuit of the suppression coil and of the capacitance of the network is significantly detuned for the fundamental frequency of the network, a high value of the auxiliary signal is needed to induce a measurable response on the voltage of the network node. It is therefore necessary to use an auxiliary signal generator with high power, which is expensive, bulky, and has a large weight. This problem stands out particularly for larger networks with very high damping, in which during a significant detuning of the circuit for frequencies close to the nominal frequency of the network, the resulting voltage response can not be measured with an accuracy sufficient for evaluating the tuning of the given resonant circuit. Generally, for known devices, changes in size of the auxiliary signal are used for the necessary change in the level of the monitored signal.

Known devices also used for generating an auxiliary signal use various methods of switching either of rectangular voltage pulses or of voltages of the fundamental frequency of the network, by which signals are formed with a broad frequency spectrum from which it is necessary, either through analog or digital, to filter only a relatively small portion carrying the information necessary for evaluating the state of tuning of the resonant circuit. This part of the signal is then used to calculate a number of parameters of the network, the results of which are significantly affected by the accuracy of the measurement of the given components of the resulting auxiliary current signal and the voltage response of the resonant circuit. Adjusting the arc suppression coil is therefore inaccurate; the measurement and evaluation cycle must be repeated many times and often exceeds the optimum value of inductance of the arc suppression coil, so that the adjustment process is extended. A large part of the energy used to generate the auxiliary signal is still lost for the evaluation of the state of the network. The values of the auxiliary current signal are controlled indirectly by changing the switching of the auxiliary voltage; a different current signal is therefore introduced for different states of tuning of the resonant circuit and for different values of the natural unbalance of the network.

The objective of the invention is therefore to find such a method and device for automatic tuning of a continuously and/or discretely tunable arc suppression coil which allows for the evaluation of the state of tuning of the resonant circuit formed by the arc suppression coil and by the total capacitance of the network to the ground potential in all realistically considerable states of its detuning, even for very large networks of an electricity system. The resulting method of evaluation must be energy-saving but still resistant to errors of measuring small signals, without the need to use, for the greater accuracy of measurement and evaluation, merely an increase in the level of the auxiliary signals used. Summary of the invention

This object is achieved by creating a method and device for automatic setting a continuously and/or discretely tunable arc suppression coil in the compensated network of an electric system according to the present invention. The correct setting of a tunable arc suppression coil secures the compensation of the capacitive component of the earth-fault current which occurs as a result of earth-faults in one of the phase conductors of the electrical system, for example, typically in the electricity distribution system.

The invention is based on a new multi-frequency method, the substance of which may be characterized as generating and supplying an auxiliary current or voltage signal with a continuously variable, discretely variable, or spectrally composed angular frequency with a pair of complementary frequency components, and the use of these specially generated frequency components in a new way to tune the arc suppression coil and to compensate the system.

The method according to the invention can be carried out in two variants which are based on a common principle of a variable angular frequency, or more angular frequencies, of the auxiliary signal and on a simple method of using system response without the need for complicated calculations and with minimum demands on measurement accuracy.

The basis of the first method of setting the continuously and/or discretely tunable arc suppression coil according to the present invention lies in the idea that a frequency analysis is carried out of the resonant circuit, which is formed by the inductance of the arc suppression coil and by the capacitance of the electrical system to the ground. The auxiliary signal is introduced to the point of the zero-sequence component of the electrical system in the form of current or voltage with variable angular frequency. The frequency of the auxiliary signal may be continuously variable or discretely variable; it varies preferably in the range from 10 to 250 Hz. For the period that the auxiliary signal is supplied, the voltage or the current of the zero-sequence component varies depending on the change of the angular frequency. When evaluating the measured voltage of the zero-sequence component, such an angular frequency is sought when the size of the effective and/or maximum value of the measured voltage is the largest. A similar process is followed when evaluating the measured current of the zero-sequence component, where the size of the effective and/or maximum value of the measured current is the smallest. Then the

angular frequency corresponds exactly to the resonance angular frequency If the found

resonance angular frequency is larger than the fundamental angular frequency of the electrical system, the arc suppression coil is overtimed, meaning that the electrical system is overcompensated. If the found resonance angular frequency is lower than the

fundamental angular frequency of the electrical system, the arc suppression coil is undertuned, meaning that the electrical system is undercompensated. If the found resonance of the angular frequency is equal to the fundamental angular frequency of the electrical system , the arc suppression coil is tuned, meaning the electrical system is compensated. A value of in comparison with the value thus determines the direction of tuning of the arc suppression coil. The steps according to the first method are cyclically repeated until the tuning of the arc suppression coil and compensation of the electric system achieve the required accuracy. On the basis of the determined value of the resonance angular frequency the total capacitance C against the ground can be determined at any moment by the relationship where L is the inductance of the arc suppression coil. The value of

total capacitance C of the system appears as basic information about the actual range of the electrical system.

The first method can be used to automatically adjust the arc suppression coil independently, but it is more demanding concerning the computing power of the evaluating unit and the control unit of the generator of the auxiliary signal during the tuning process.

The second method of setting the continuously and/or discretely tunable arc suppression coil according to the present invention consists in the idea that for each angular frequency different from the fundamental angular frequency of the electrical system, such a complementary angular frequency , can be determined which lies below or above the size of the fundamental angular frequency of the distribution system from the relationship . For such a determined pair of complementary frequency components, respectively

their angular frequencies it is true that the response of the system to the auxiliary signals of these frequencies with the same amplitude is in absolute and/or effective value equally large in the very situation in which the resonant circuit composed of a capacitance network and inductance of the arc suppression coil is in resonance for the fundamental angular frequency of the network . The auxiliary signal must contain at least two complementary frequency components of angular frequencies , but for refining the setting of the arc suppression coil it is possible to use several pairs of complementary frequency components. Both complementary frequency components of one pair of the auxiliary signal may be continuously variable and/or a discretely variable, but the rule is always maintained that the angular frequency of one complementary component is a quotient of the square of the fundamental angular frequency of the system and of the angular frequency ω,,- of the second complementary frequency component, namely , where are angular frequencies of the first and second complementary frequency

components. An evaluation of the measured voltage or current of zero-sequence component seeks to find such a position of the arc suppression coil where the size of the effective and/or maximum values of the measured voltage or current of both complementary frequency components with angular frequencies are equal. Even the second method according to the invention can be used to set the arc suppression coil independently. On the basis of the measured response of the electrical system when carrying out the second method according to the invention, it is then very easy possible to determine the actual damping G of the zero electrical system and the value of the actual detuning of the arc suppression coil, alternatively all of arc suppression coils connected to the neutral points of the electrical system. Subsequently, the actual inductance L of the arc suppression coil may also be set, respectively the actual resulting inductance of sum of all arc suppression coils connected to the neutral points of the electricity system and the capacitance of the entire electrical system to the ground.

If the monitored voltage or current of the response of the system falls below or exceeds a preselected threshold value, the angular frequencies of both frequency components continuously and/or discretely change according to this proportion so that the response of the system stays within tolerance, while the proportion must still be maintained. The

predefined threshold values are determined specifically for each electrical system and there exist requirements of precision for the measurement, i.e. the size of the value of the voltage or current, which are still eligible for capturing their changes, as well as the requirement for limitation of the voltage of the zero-sequence component which, at too high of a value, could cause undesired high-value phase voltage unbalance of the system, alternatively the undesirable function of signaling the earth fault.

One of the complementary angular frequencies used at the beginning of the tuning process can preferably be the resonant frequency of the network determined through frequency analysis of the resonant circuit according to the first method of setting the continuously and/or discretely tunable arc suppression coil. To this is then determined the complementary angular frequency satisfying the condition In a preferred embodiment of the invention,

both alternative ways to set the arc suppression coil can thus be connected in mutual succession, whereby the best and most accurate results are achieved of setting the arc suppression coil, its tuning, and the operation of the network in the compensated state. All variants of the method of setting the arc suppression coil can be applied both in the fault-free state of the electrical system and preferably also in the period of duration of the earth-fault in the electrical system network.

Selecting as one of the complementary angular frequencies ensures that the network response in the initial phase of tuning the arc suppression coil according to the second method will be sufficient for this frequency component of the auxiliary signal, respectively within the tolerance needed for accuracy of the measurement, whereas in a situation in which the actual detuning of the system is not too large, it will most likely not be necessary to change the frequencies of the used complementary components of the auxiliary signal during the process of tuning.

The first and second method of setting the arc suppression coil according to the invention enables problem-free operation and especially the possibility of simultaneous tuning of any number of parallel operating arc suppression coils in a single electrical system connected to one or more different neutral points of the electrical system. A device using a method of tuning according to the invention immediately evaluates only the response of the electrical system in a single variable (voltage or current) for the given complementary pair of angular frequencies of the auxiliary signal. In the method of tuning arc suppression coils according to the invention, no processes or calculations are used which are affected by the activities of other devices tuning other arc suppression coils connected in parallel in the same system, unlike the hitherto known methods of setting an arc suppression coil.

The essence of the device for setting the continuously and/or discretely tunable arc suppression coil according to the present invention lies in the fact that it performs the requested changes of the angular frequency of the auxiliary signal and/or generates at least one pair of complementary frequency components of the auxiliary signal according to the said methods. The device sets not only the various sizes of the angular frequency of the auxiliary signal, but also the sizes of its amplitudes and angles of the phase shifts. According to a preferred embodiment of the invention, the device meets these requirements based on a frequency inverter. Control and regulation of the frequencies, amplitudes, and phase shift angle(s) of the auxiliary signal(s) is performed using appropriate software and hardware, e.g. using control systems based on DSP (Digital Signal Processor) microcontroller technologies and/or programmable logic arrays FPGA (Field Programmable Gate Array).

In the first preferred embodiment of the device according to the invention, designed for carrying out the first method of automatic setting at least one continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system, the evaluation unit of the response of the electrical system, control unit, and the auxiliary signal generator are adapted to generate the auxiliary signal with the possibility of a continuous or discrete change in the angular frequency, amplitude, and phase shift angle, and the device is provided with hardware and software means for carrying out the automatic adjustment of the arc suppression coil according to the first method.

In the second preferred embodiment of the device according to the invention, designed for carrying out the second method of automatic setting at least one continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system, the evaluation unit of the response of the electrical system, control unit, and the auxiliary signal generator are adapted to generate an auxiliary signal containing at least one pair of complementary frequency components with the same amplitude and with angular frequencies for which the relationship applies, where is the fundamental angular

frequency of me system, while and the device is equipped with hardware and software means for carrying out automatic adjustment of the arc suppression coil according to the second method. For this device it is also advantageous if the control unit and the auxiliary signal generator are also adapted for a continuous or discrete change in angular frequencies of the pair of complementary frequency components of the auxiliary signal, their amplitude, and the phase shift angle.

There are many possibilities of carrying out the hardware of the above described devices, wherein these possibilities are known to professionals. However, it is important that the device contain a software module for controlling the angular frequency of the auxiliary signal for continuous or discrete change of the angular frequency of the auxiliary signal and/or for generating at least one pair of complementary frequency components with the angular frequencies according to the relationship is the fundamental

angular frequency of the system.

Also, this software module for controlling the angular frequency of the auxiliary signal and evaluating the response of the electrical system is preferably adapted for continuous or discrete change in angular frequencies of pairs of complementary frequency components of the auxiliary signal, their amplitude, and phase shift angle, and preferably is part of the evaluation unit and/or control unit.

Connecting the device according to the invention into an electrical system is advantageous in embodiments where the auxiliary signal generator is connected to at least one point of a zero- sequence component of an electrical system via at least one device from the group of: single- phase transformer, arc suppression coil, grounding transformer, Bauch-transformer.

The subject of the invention is also a program of an evaluation unit and/or control unit of the auxiliary signal generator in a device for automatic setting a continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system which includes instructions for carrying out the first or second method of automatic setting the arc suppression coil or possibly a method formed by a merging of the first and second methods.

The method and device for automatic setting the arc suppression coil according to the invention offers many advantages over known methods and devices, notably the following advantages:

For the actual process of tuning the arc suppression coil, it is not necessary to measure the auxiliary signal itself. For the basic process of tuning, the calculations of the system parameters sensitive to the measurement accuracy of the auxiliary signal and the corresponding response of the resonant circuit formed by the capacitance of the electrical system and induction of the arc suppression coil or more arc suppression coils are not used.

Injecting an auxiliary signal and evaluating the response of the electrical system to it can be carried out also during the ongoing change in the tuning of the resonant circuit, thus, for example, during the tuning of the arc suppression coil or during changes in the range i.e. of the capacitance of the electrical system. It is not necessary that the resonant circuit is in a steady state during measurement. Thanks to the sustained comparison of the response of the electrical system to at least two complementary frequencies, when using the presented second method of tuning, the actual state of attunement {undercompensated, overcompensated, tuned) is continually known. Known methods require the execution of calculations of the parameters of the electrical system from values measured in a steady state (in the suppression coil's idle state without network changes).

To achieve a change in the size of an electrical system response to an auxiliary signal, it is not necessary to change the size of this auxiliary signal; more appropriate frequency(ies) of the auxiliary signal is(are) only used for the actual state of the electrical system. Even for systems with high-value ground capacitive current, i.e. for large-scale systems, it is not necessary, in comparison with known methods and devices, to significantly improve the power and hence the costs for devices used to generate auxiliary signals for tuning arc suppression coils.

The parallel cooperation of multiple systems of tuning interconnected in a single electrical system using the method of tuning arc suppression coils according to the present invention is, for the basic task of finding resonance, trouble-free even without the need of communication, i.e. it is not necessary to establish a dedicated communication route for this purpose. Hitherto known devices require, to enable parallel cooperation of multiple systems of tuning interconnected into a single electrical system, the use of communication means for mutual cooperation. Usually, this cooperation is carried out in such a way that one device controls the function of the other devices operating in the same network. For complex electrical systems with many configuration possibilities, the realization of all relevant communication interconnections is very difficult and costly, which is completely eliminated by the method and device according to the invention.

Description of the drawings

The invention will be explained in more detail by means of drawings which show:

Fig.l curve 1 of the voltage value of a zero-sequence system as a frequency response of the electrical system to a generated auxiliary current signal with a continuously variable frequency curve 2 of the current value of a zero-sequence system as frequency response of the system to a generated voltage signal with continuously variable angular frequency

Fig.2 the resonance curve of an electrical system dependent on the variable tuning of the resonant circuit (variable inductance of the arc suppression coil) for auxiliary current signals of different angular frequencies,

Fig.3 an example of the connection of the device according to the invention,

Fig. 4 a block diagram of the connection of the device according to the invention.

Examples of the preferred embodiments of the invention

It is understood that the hereinafter described and illustrated specific examples of the realization of the invention are presented for illustrative purposes and not as a limitation of the examples of the realization of the invention to the cases shown herein. Experts who are familiar with the state of technology shall find, or using routine experimentation will be able to determine, a greater or lesser number of equivalents to the specific realizations of the invention which are specifically described here.

The first example of the realization of the method of automatic setting an arc suppression coil 9 for compensating the electrical system 10 according to the invention uses a frequency analysis of the resonant circuit formed by the capacitance C of the distribution network of an electrical system 10 to the ground and by an arc suppression coil 9. For the auxiliary signal 14 with continuously or discretely varied frequency applied to the node i.e. to the neutral point of the electrical system 10, a response of the circuit can be evaluated for each angular frequency of this auxiliary signal 14. The angular frequency of the auxiliary signal 14 is changed continuously, or by discrete values, wherein the frequency of the auxiliary signal 14 varies in a range from 10 Hz to 250 Hz. When using the auxiliary signal 14 in the form of an injected current, the response of the electric system 10 achieves, in the form of node voltage to the ground, the greatest value at the resonant frequency corresponding to the actual tuning of the electrical system 10. If this angular frequency is different from the fundamental angular frequency of the electrical system 10, i.e. the resonant circuit for the fundamental angular frequency ω,, is detuned.

Similarly, a frequency analysis of the response of the electric system 10 can be used in the form of a current to its neutral point caused by the auxiliary signal 14 in the form of voltage applied between the neutral point of the electrical system 10 and the ground. In this case, the monitored quantity, e.g. the current, acquires its minimum at the resonant angular frequency

Fig. 1 shows the curve 1 of the frequency response of an electrical system 10 on the supplied auxiliary current signal 14 with a variable angular frequency. When supplying the auxiliary signal 14 as a current with constant amplitude and variable angular frequency to the neutral point of the electrical system 10, the response of the node voltage of the electric system 10 to the ground potential for the given angular frequencies is monitored. This voltage reaches the highest amplitude with the introduction of a current with angular frequency equal to the resonance of the angular frequency of the network at the given actual tuning.

Curve 2 in Fig. 1 shows the frequency response of the electrical system 10 on a generated voltage auxiliary signal 14 with variable angular frequency. When supplying the auxiliary signal 14 in the form of voltage with constant amplitude and variable frequency, connected between the neutral point of the electric system 10 and the ground, the response in the form of a current flowing into the node of the electrical system 10 is monitored. This current reaches the lowest amplitude upon the connection of voltage with the angular frequency equal to the resonance angular frequency of the network at the given actual tuning.

If a resonant angular frequency is found which coincides with the fundamental angular frequency of the electrical system 10, the arc suppression coil 8 is tuned to the very resonance with a total ground capacitance of the electrical system 10, i.e. the electrical system 10 is compensated for the fundamental angular frequency

If the found resonance angular frequency is greater than the fundamental angular frequency of the electrical system 10, the arc suppression coil 9 is overtuned, meaning that the electrical system 10 is overcompensated. If the found resonant angular frequency is smaller than the fundamental angular frequency _s of the system 10, the arc suppression coil 9 is undertuned, meaning that the electrical system 10 is undercompensated. For fine-tuning an overtuned arc suppression coil 9, the command is given to increase the inductance L of the arc suppression coil 9; for fine-tuning an undertuned arc suppression coil 9, the commanded is given, in contrast, to lower the inductance L of the arc suppression coil 9.

For an electrical system 10 which is compensated, applies.

For an electrical system 10 with an overtuned arc suppression coil applies.

For an electrical system 10 with an undertuned arc suppression coil applies.

A second example of realization of the method of automatic setting an arc suppression coil 9 for compensating the electrical system 10 according to the invention is based on the generation of an auxiliary signal 14 with at least one pair of complementary frequency components with the same amplitude and with angular frequencies for which it applies that

To find such a position of the arc suppression coil 9, in which there occurs a resonance between its inductive reactance and capacitive reactance of the electrical system 10 to the ground for the fundamental angular frequency the fact is used that for each angular frequency ωι of the auxiliary signal 14 different from the fundamental angular frequency t¾, such a complementary angular frequency can be determined for which the resonance curve acquires the same value at the very point where the resonance curve for the fundamental angular frequency of the network reaches its peak. Analogically, the resonance curves of the current can be drawn up with the use of auxiliary signals 14 in the form of voltage of various angular frequencies

Fig. 2 shows the resonance curves of the electrical system 10 depending on the variable tuning of the resonant circuit (variable inductance L of arc suppression coil 9) for the auxiliary signals 14 of various angular frequencies This is a resonant curve 3 of the voltage response of the frequency component with angular frequency for which the curve

7 for the angular frequency is complementary. Another complementary pair is represented by the resonance curves 4, 6. When supplying the auxiliary signal 14 in the form of currents with equally large amplitudes and different angular frequencies the response of the

resonant circuit in the form of a zero-sequence voltage of the electrical system 10 with the given angular frequency represents the resonance curve with a peak at the point when the actual tuned inductive reactance arc suppression coil 9 and capacitive reactance of the electrical system 10 to the ground are in resonance for the given angular frequency. For the fundamental angular frequency of the network (curve 5), this point corresponds to the desired inductance L of the arc suppression coil 9 and represents a resonant inductance Lsrez corresponding to the capacitive earth current of the electrical system 10 for its fundamental angular frequency For higher angular frequencies, this point is located to the right of this position, i.e. in the area where the arc suppression coil 9 for the fundamental angular frequency is overtimed; for lower angular frequencies it is located in the area where the arc suppression coil 9 is undertuned for the fundamental angular frequency

The voltage of the zero-sequence component as a response of the system 10 to a supplied current auxiliary signal 14 of size / and angular frequency can be expressed as:

A tuned state of a resonant circuit formed by arc suppression coil 9 with inductivity L and with total capacitance C of an electrical system 10 to the ground is, for the fundamental angular frequency of network achieved if the following conditions are met:

From these conditions it applies that the size of the response of the electrical system 10 for identically large amplitudes of auxiliary signals 14 with the angular frequencies of respectively the amplitude of the response of the electrical system 10 to these auxiliary signals 14 is the same, so long as their angular frequencies satisfy the condition:

Because for finding the resonant inductance of the arc suppression coil 9 the angular frequencies different from the fundamental angular frequency of the system 10 are used, the proposed method according to the invention is resistant to interfering signals of an angular frequency equal to the fundamental angular frequency of the electrical system 10. The tuning is thus not affected by the natural unbalance of the electric system 10 causing a natural resonant voltage curve for the fundamental angular frequency of the system 10. Tuning is also not affected by fluctuations in the zero-sequence voltage of the electrical system of 10 of the fundamental frequency induced by fluctuations of unbalanced loads of the electrical system 10.

In a third example of the implementation of the method according to the invention, the first and second method are substantially combined. One angular frequency of the complementary frequency components preferably used can be, at the beginning of the tuning process, the resonant angular frequency of the network determined through a frequency analysis of the resonant circuit according to the first method of setting the arc suppression coil 9 while the angular frequency satisfying the condition can be set as complementary. In a

preferred embodiment of the invention, both alternative methods of setting the arc suppression coil can thus be combined in mutual succession, whereby the best and quickest results of setting the arc suppression coil 9, its tuning, and the operation of the electrical system 10 in a compensated state are achieved.

After determining the resonance tuning of arc suppression coil 9 for the fundamental angular frequency of the network, this arc suppression coil 9 can be tuned to the desired position, thus according to the desired degree of the detuning of the entire circuit. By common practice, the size of this detuning can be determined in the absolute value as the difference of the set current value of the arc suppression coil 9 and the value of this current in the point of resonance for the fundamental angular frequency of the system 10 or relatively as a proportionate part of the actual value of the resonant current for the fundamental angular frequency of the electrical system 10.

For each pair of complementary frequency components with angular frequencies of the auxiliary signal 14, it is possible, from the value of the auxiliary signal 14 and from the measured response of the electrical system 10, to calculate the actual damping G of the zero system of the electrical system 10, for which the following applies:

Using a simultaneous measurement of the complementary frequency components of the auxiliary signal 14 and from the measured response of the electrical system 10, it is also possible to calculate the specific value of the actual inductance L corresponding to the current of the arc suppression coil 9, alternatively the sum of all arc suppression coils 9 actually connected to the neutral points of the given electric system 10 and the actual capacitance of the entire electrical system 10 to the ground.

If the imaginary component of the detected admittance Yi resp. Yn for a given angular frequency resp. is marked as follows

respectively then the detuning of the electrical system 10 for the fundamental angular frequency can be calculated according to the relationship:

In absolute current value expressed in amperes, the resonant circuit is detuned for the fundamental angular frequency <¾ at phase voltage of the electrical system 10 of size as follows:

The inductance L of arc suppression coil 9, respectively the total inductance of all arc suppression coils 9 in the node of the electrical system 10 can be expressed as follows:

and

The capacitance of the entire electrical system 10 to the ground can be expressed as follows:

and

The calculated parameters of the electrical system 10 can be displayed and/or recorded. For the basic function of determining such a position of the arc suppression coil 9 in which the resonant circuit is tuned, it is not necessary, according to the present invention, to use the above-mentioned calculations; in principle it is not even necessary, for the actual tuning procedure, to measure the actual value of the auxiliary signal 14, so long as it is generated by a device 13 securing, for the entire used frequency range, the same size of this auxiliary signal 14. The calculations mentioned above, according to known methods, and their results can be used for the informative displaying of the parameters of the electrical system 10.

Fig. 3 and fig. 4 depict a diagram of the device 13 for carrying out the methods of setting the arc suppression coil 9 according to the invention. To the neutral point of the electrical system 10 there is connected a continuously and/or discretely tunable arc suppression coil 9 which has auxiliary winding. The auxiliary signal 14 is generated in the generator 8 of the auxiliary signal 14 which is formed by a frequency converter and a filter. The generator 8 is connected to the auxiliary winding of the arc suppression coil 9 and is controlled by the control unit 12 of the converter. The evaluation unit 11 monitors the response of the electric system 10 to the auxiliary signal 14 and commands the control unit 12 of the generator 8 and the drive of the arc suppression coil 9.

The generator 8 is capable of ensuring the generation of one frequency component and/or pair of complementary frequency components of the auxiliary signal 14 with variable angular frequency and carrying out the required change of the angular frequency according to the aforementioned methods. The control unit 12 of the generator 8 sets not only the varying sizes of the angular frequency of the auxiliary signal 14, but also the sizes of its amplitudes and phase shift angles. These requirements are satisfied by the device 13 on the basis of frequency converters. Control and regulation of the angular frequency, amplitudes and phase shift angle of the auxiliary signal 14 is carried out using conventional software and hardware means, e.g. using control systems based on DSP microcontroller technology and/or FPGA programmable logic arrays, into which there is implemented the software module 15 of the control of the frequency of the auxiliary signal 14 and the evaluation of the response of the electrical system 10 comprising a sequence of instructions for carrying out the above described methods for automatic setting the arc suppression coil 9. Analogically, for connecting the generator 8 to the electrical system 10, one may use e.g. a single-phase transformer connected between the neutral point of the network and the ground potential, a special grounding transformer, Bauch transformer, and the like.

Industrial applicability

The method and device according to the invention can be used for automatic setting a continuously and/or discretely tunable arc suppression coil in the compensated network of an electrical system for the correct compensation of earth-fault currents which occur as a consequence of an earth-fault in the distribution system.

Overview of the positions used in the drawings

1 curve of frequency response of the electrical system to the generated current signal with variable frequency

2 curve of frequency response of the electrical system to the generated voltage signal with variable frequency

3 resonance curve of voltage response of frequency component with angular frequency ωi complementary to the resonance curve 7

4 resonance curve of voltage response of the frequency component with angular frequency ωi complementary to the resonance curve 6

5 resonant curve of voltage response for the fundamental angular frequency ωs

6 resonance curve of voltage response of the frequency component with angular frequency ωii complementary to the resonance curve 4

7 resonance curve of voltage response of the frequency component with angular frequency ωii complementary to the resonance curve 3

8 auxiliary signal generator

9 arc suppression coil

10 electrical system

11 evaluation unit

12 control unit

13 device for automatic setting of the arc suppression coil

14 auxiliary signal

15 control module for frequency of auxiliary signal and for evaluating the response of the electrical system

C total capacitance of the system to the ground

G damping of the zero-sequence system of the electrical system i.e. conductance

(total active component of admittance) of the zero-sequence system of the electrical system

current and voltage of zero-sequence component as a function of

angular frequency ω

phasor of current and voltage of zero-sequence component with angular frequency

phasor of current and voltage of zero-sequence component with angular

frequency

L inductance of arc suppression coil

resonant inductance of arc suppression coil at fundamental angular frequency

susceptance (total reactive component of admittance) of system at angular frequency

susceptance of system at angular frequency

admittance of system at angular frequency ,

Yi admittance of system at angular frequency

detuning of the system for fundamental angular frequency

angular frequency

angular frequency different from the fundamental angular frequency of the system

complementary angular frequency to angular frequency

complementary angular frequency

resonance angular frequency

fundamental angular frequency of the system

Claims

1. A method of automatic setting at least one continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10) comprising the generation of an auxiliary current or voltage signal (14), supplying this auxiliary signal (14) to the point of a zero-sequence component of the electrical system (10) and monitoring the response of the electrical system (10) to the auxiliary signal (14) and its change, wherein the auxiliary signal (14) comprises at least one frequency component, c h a r a c t e r i z e d i n t h a t : a) the angular frequency of the frequency component of the auxiliary signal (14) continuously or discretely changes, b) a frequency analysis of the resonant circuit is subsequently carried out which is formed by the inductance (L) of the arc suppression coil (9) and the capacitance (C) of the electrical system (10), wherein the resonance angular frequency is determined for which the greatest responses of the electrical system (10) are achieved, i.e. the greatest effective or maximum values of the measured voltage and/or the smallest effective or maximum values of the measured current c) the value of the resonant angular frequency is compared with the fundamental angular frequency of the electrical system (10), d) if the value is the arc suppression coil (9) is undertuned and the system (10) is undercompensated, a reduction of the inductance of the arc suppression coil (9) is carried out, wherein steps a) to c) are repeated until the compensation of the electrical system (10) is achieved with the required accuracy, e) if the value is the arc suppression coil (9) is overtimed and the electrical system (10) is overcompensated, an increase in the inductance of the arc suppression coil (9) is carried out, wherein steps a) to c) are repeated until the compensation of the electrical system (10) is achieved with the requtred accuracy, if the value is the arc suppression coil (9) is tuned and the electric system (10) is compensated.

A method according to claim 1, c h a r a c t e r i z e d i n t h a t the change in frequency of the frequency component of the auxiliary signal (14) is carried out in the range from 10 to 250 Hz.

A method according to claim 1 or 2, c h a r a c t e r i z e d i n t h a t on the basis of the determined value of the resonant angular frequency the capacitance (C) of the electrical system (10) to the ground is determined on the basis

of the relationship where L is the inductance of the arc suppression coil (9)

or the resulting inductance of all arc suppression coils (9) in the electrical system (10).

A method of automatic setting at least one continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10) comprising the generation of an auxiliary current or voltage signal (14), supplying this auxiliary signal (14) to the point of a zero-sequence component of the electric system (10) and monitoring the response of the electrical system (10) to the supplied auxiliary signal (14) and its change, wherein the auxiliary signal (14) is generated with at least one pair of frequency components, c h a r a c t e r i z e d i n t h a t the frequency components of each pair are complementary, have the same amplitude, and for their angular frequencies the relationship applies, where (¾ is

the fundamental angular frequency of the electrical system (10), where the first frequency component has an angular frequency and where the second frequency component has an angular frequency lying above or below the value (cos) according to the above described relationship, the response is measured of the electrical system (10) on the supply of the auxiliary signal (14) with a pair of frequency components with angular frequency

wherein the responses are compared of the electrical system (10) for both frequency components, thus measuring the effective and/or maximum values of the voltage c) based on the difference of the measured values

a change of inductance of the arc suppression coil (9) is carried out so that when d) if the value is and/or if the value is , the

arc suppression coil (9) is undertuned and the electrical system (10) is undercompensated, the inductance of the arc suppression coil (9) is reduced, e) if the value is and/or if the value is the

arc suppression coil (9) is overtimed and the electric system (10) is overcompensated, the inductance of the arc suppression coil (9) is increased, f) steps b) to e) are repeated until such a tuning by the arc suppression coil (9) and compensation of the electrical system (10) is achieved, i.e. such value of inductance of the arc suppression coil (9) at which, for the size of the effective and/or maximum values of the measured response of the electrical system, applies with the required

accuracy.

5. A method according to claim 4, c h a r a c t e r i z e d i n t h a t after carrying out steps a) and b), the measured values ( ) are compared with predefined limit values that determine the requirements of measurement accuracy as well as the requirement for limiting the voltage of the zero- sequence component, and if the measured values of the response of the electrical system (10) lie outside the interval specified by the limit values, a continuous or discrete variation change is carried out of angular frequency of the frequency components of the auxiliary signal (14), while maintaining the relationship and the response of the electrical system (10) is

measured again until the measured values u are not within the interval defined by the limit values, and then the steps c) to f) according to claim 4 are carried out.

6. A method according to claim 4 or 5, c h a r a c t e r i z e d i n t h a t the angular frequency of the first complementary frequency component is, in step

a), determined as the value where the value z is determined such that the angular frequency the auxiliary signal (14) continuously or discretely changes, and then a frequency analysis of the resonant circuit is carried out, which is formed by the inductance (L) of the arc suppression coil (9) and the capacitance (C) of the electrical system (10), wherein the resonance angular frequency is determined for which the largest effective or maximum values of the measured voltage and/or the least effective or maximum values of the measured current are achieved.

7. A method according to any one of claims 4 to 6, c h a r a c t e r i z e d i n t h a t for each pair of complementary frequency components of the auxiliary signal (14), the actual damping (G) of the zero system of the electrical system (10) is established from the value of the auxiliary signal (14) from the measured response of the electrical system (10) according to the relationship: furthermore, the value of actual of detuning of the arc suppression coil (9) or all arc suppression coils (9) connected to the neutral points of the electrical system (10) is determined, wherein the imaginary component is determined of the detected admittances for the angular frequency of the complementary components: and subsequently the detuning of the electrical system (10) is determined for the fundamental angular frequency according to the relationship:

8. A method according to claim 7, c h a r a c t e r i z e d i n t h a t subsequently the determined actual inductance (L) of the arc suppression coil (9) resp. the actual resulting inductance (L) of all arc suppression coils (9) is determined in the node (nodes) of the electrical system (10) according to the relationship:

and the capacitance (C) of the entire electrical system (10) to the ground is determined according to the relationship:

9. A method according to any of claims 1 to 8, c h a r a c t e r i z e d i n t h a t at least two arc suppression coils (9) in the same compensated network of the electrical system (10) are tuned simultaneously.

10. A method according to any one of claims 1 to 9, c h a r a c t e r i z e d i n t h a t at least one arc suppression coil (9) is tuned during the period of duration of an earth-fault in the network of the electrical system (10).

11. A device (13) for automatic setting at least one continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10) by supplying an auxiliary current or voltage signal (14) to the point of a zero-sequence component of an electrical system (10) from a generator (8) of the auxiliary signal (14) controlled by a control unit (12) and by monitoring the response of the electrical system to the supplied auxiliary signal (14) and its change using an evaluation unit (11) which commands the control unit (12), wherein the auxiliary signal (14) has at least one frequency component, c h a r a c t e r i z e d i n t h a t the evaluation unit (11), control unit (12), and generator (8) of the auxiliary signal (14) are adapted for generating the auxiliary signal (14) with the option of continuous or discrete change in the angular frequency, amplitude, and phase shift angle, and the device (13) is provided with hardware and software means for carrying out the automatic setting of the arc suppression coil (9) by the method according to any one of claims 1 to 3, 9, 10.

12. A device (13) for automatic setting at least one continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10) by supplying an auxiliary current or voltage signal (14) to the point of a non-rotational component of an electrical system (10) from a generator (8) of the auxiliary signal (14) controlled by a control unit (12) and by monitoring the response of the electrical system to the supplied auxiliary signal (14) and its change using an evaluation unit (11) which commands the control unit (12), wherein the auxiliary signal (14) has at least one frequency component, c h a r a c t e r i z e d i n t h a t the evaluation unit (11), control unit (12), and generator (8) of the auxiliary signal (14) are adapted for generating the auxiliary signal (14) comprising at least one pair of complementary frequency components with the same amplitude and with angular frequencies for which the relationship applies, where is the

fundamental angular frequency of the system (10), wherein and the device (13) is provided with hardware and software means for carrying out the automatic setting of the arc suppression coil ( 9) by the method according to any one of claims 4 to 10.

13. The device according to claim 12, c h a r a c t e r i z e d i n t h a t the evaluation unit (11), control unit (12) and generator (8) of the auxiliary signal (14) are adapted for continuous or discrete change in angular frequencies ) of the pairs of complementary frequency components of the auxiliary signal (14), their amplitudes, and phase shift angles.

14. A device according to claim 11 or 12, c h a r a c t e r i z e d i n t h a t it comprises a software module (15) for controlling the angular frequency of the auxiliary signal (14) for continuous or discrete change in the angular frequency of the auxiliary signal (14) and/or for generating at least one pair of complementary frequency components with angular frequencies according to the relationship where is the fundamental angular frequency of the system (10).

15. A device according to claim 14, c h a r a c t e r i z e d i n t h a t the software module (15) for controlling the frequency of the auxiliary signal (14) is adapted for continuous or discrete change in angular frequencies of the pair of complementary frequency components of the auxiliary signal (14), their amplitudes, and phase shift angles.

16. A device according to claim 14 or 15, c h a r a c t e r i z e d i n t h a t the software module (15) for controlling the frequency of the auxiliary signal (14) and evaluating the response of the electrical system (10) is part of the evaluation unit (11) and/or control unit (12).

17. A device according to any one of claims 11 to 16, c h a r a c t e r i z e d i n t h a t the generator (8) of the auxiliary signal (14) is formed by a frequency converter.

18. A device according to any one of claims 11 to 17, c h a r a c t e r i z e d i n t h a t the generator (8) of the auxiliary signal (14) is connected to at least one point of the zero-sequence component of the electrical system (10) by at least one device from the group: single-phase transformer, arc suppression coil (9) grounding transformer, Bauch transformer.

19. A program for an evaluation unit (11) and/or control unit (12) of the generator (8) of the auxiliary signal (14) in a device (13) according to any one of claims 11, 14 to 18, for automatic setting a continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10), c h a r a c t e r i z e d i n t h a t it includes instructions for implementing the method of automatic setting the arc suppression coil (9) according to any of claims 1 to 3, 9, 10.

20. A program for an evaluation unit (11) and/or control unit (12) of the generator (8) of the auxiliary signal (14) in a device (13) according to any of claims 12 to 18 for the automatic setting a continuously and/or discretely tunable arc suppression coil (9) in the compensated network of an electrical system (10), c h a r a c t e r i z e d i n t h a t it includes instructions for implementing the method of automatic setting the arc suppression coil (9) according to any one of claims 4 to 10.