RU2389116C1 - Method for acquisition of detecting criterion of short circuit on power transmission line in case of overload, oscillation and asynchronous mode in power system - Google Patents

Abstract

FIELD: electric engineering. ^ SUBSTANCE: according to method, electrical signal is generated from currents of three phases, for instance in power transmission line, in compliance with a certain rule, and as short circuit takes place on the line with transition process, the signal would contain an aperiodic component in its structure, which is used as detecting criterion indicating occurred short circuit. This detecting criterion may be discovered, for instance by available method of electric signal processing, as a result of which information signal is generated in the form of a certain decaying sinusoidal signal with permanent frequency fadd and which may be used in logics of according devices functioning, providing for proper operation of relay protection and automatics. ^ EFFECT: method reliability improvement. ^ 4 dwg

Description

The invention relates to the field of electrical engineering, in particular to methods and devices that, when a short circuit occurs (short circuit), ensure the proper functioning of certain types of relay protection and emergency automation, for example, distance protection during short circuit on a power line in overload mode, synchronous swing or in asynchronous mode in the power system, and free transients during short circuit have an aperiodic decaying character due to the predominance of passive elements of active-inductance in the system of a different nature.

Technically similar to the present invention are methods and, on their basis, devices for preventing incorrect actions of relay protection during overloads, swing and asynchronous mode (blocking device during swings - UBK) and using as an indication of the occurrence of short-circuit the appearance of a negative sequence current in three-phase phase currents voltage system or current increment rate of the negative sequence. In some cases, the zero-sequence current that appears with some types of short circuit is taken into account. It is assumed that a symmetric three-phase short circuit is preceded by an asymmetric two-phase short circuit, and the correct functioning of the relay protection with permissible asymmetries in the power supply system in the operational mode, during swing or asynchronous mode, is provided by the appropriate choice of the response parameter of the response device of the control gear [Barzam AB System Automation. Ed. 3rd, rev. M .: Energy, 1973. S.137-150.].

The prototype method and the UBC based on it have inherent disadvantages, ultimately, reducing the sensitivity of detecting the occurrence of short circuits, since the response parameters of the reacting UBC body are tuned up: from the reverse sequence current under the conditions of the system with acceptable electrical asymmetry; from unbalances that occur during swing and asynchronous mode due to a possible significant difference in the frequencies of the generating sources in the power system; from unbalances caused by both a deviation from the harmonic shape of the primary currents in the power supply system and the forms of currents in the secondary circuits of current transformers to which the UBC is connected; due to the non-linearity of current transformers in some modes of their operation; due to the need to take into account the errors of current transformers. Operating on the basis of detecting electrical asymmetry in the power supply system, the UBK has a limitation in use when there are powerful asymmetric consumers of electrical energy, for example, single-phase; there is a possibility of failure of the UBK during the simultaneous operation of the contacts of the switching apparatus supplying voltage to the power line with an unassembled three-phase short circuit; incorrect operation of the filter of the appropriate sequence included in the UBK structure under transient conditions in the power supply system when a short circuit occurs in it is possible [Fabrikant V.L. Remote Protection: Textbook. manual for universities. - M .: Higher. school, 1978. S.189-208; Schneerson E.M. Digital relay protection. - M .: Energoatomizdat, 2007. P.388-395].

The invention is known [Patent No. 2311154 (RU), IPC H03D 1/00, H03C 1/00. The method of processing an electrical signal [Text] / Mamaev B.A. (RU); Applicant and patent holder North Caucasian State Technical University (RU). - No. 20051124408/09; declared 08/01/2005; publ. 08/10/2008. Bull. No. 22], according to which an electric signal consisting of two components, one of which is the sum of harmonics, is added to an additional harmonic signal, the frequency of which is much higher than the frequency of the first harmonics included in the sum of harmonics, the total signal is raised to the second positive degree and from of the received electric signal, an electric sinusoidal signal is emitted with the frequency of the harmonic signal and, by the presence of this signal, its other signal is identified in the processed electric signal which is either an aperiodic transient signal or a constant component.

Known application for invention [Mamaev V.A. A method of processing an electrical signal. No. 2008107783, declared 02/28/2008], in which a method is proposed for increasing the accuracy of identification of an aperiodic signal according to the known invention [Patent No. 2331154 (RU)].

The technical result achieved by using the present invention consists in a method for obtaining a detecting sign of the occurrence of a short circuit, for example, on a power line during overloads, rocking and asynchronous mode in the power system and consists in increasing the technical level of relay protection synthesized based on it by increasing sensitivity to the appearance of a short circuit as a result of eliminating the need to perform any detuning of its functioning from unbalances when the line is overloaded , swinging and asynchronous operation in the power system, as well as ensuring reliable detection of three-phase faults on the power line, including when the contacts of the switching apparatus are closed at the same time, for example, when the voltage is incorrectly applied to the power line with a three-phase short circuit installed on it.

The specified technical result is achieved by the fact that the proposed method of obtaining a detecting sign of the occurrence of short-circuit during rocking and asynchronous or overload mode is based on fixing the fact of the appearance of an aperiodic component in a specially formed electrical signal, provided that there is an aperiodic component in at least one of the phase currents of the three-phase power line in the transition process after the occurrence of a short circuit, and by the method of obtaining an identifying sign about the occurrence of short circuit the implementation of any detuning characteristic of the prototype method and a device based on it.

The distinguishing feature of a method for producing a mist feature of the present invention lies in the fact that from the instantaneous transmission line phase current values form an analog electric signal by a certain rule, for example, some input voltage _vh.kz u (t), a structure in which in the event of any type of RS on the power line have a free component _Σ.ap.kz u (t) of the transition process, which is used as a mist characteristic of a short-circuit on the line elektropereda and, and its presence can be identified, for example, using a selective device synthesized by a known method of processing an electrical signal [Patent No. 2331154 (RU)], while the selective device has one input and one output, and the input formed according to a certain rule analog electrical signal _Rin u (t), which transient accompanying occurrence of short-circuit, comprises a DC component and the analog output is generated at the output of the selector under these conditions Igna _O u (t) in the form of a damped sinusoidal signal associated with the presence of a mist in the form of feature DC component appearing only when the fault in the input signal _vh.kz u (t), and the presence of this component conclude the occurrence of any type of short- power lines under conditions of overload, swing and asynchronous mode in the power system, while with the perfect functioning of the selective device for identifying the aperiodic component according to the known method of processing an electrical signal hydrochloric _vyh.kz analog signal u (t) is decaying amplitude _m.ap U (t) with the structure

and the output analog signal u _{output short-circuit} (t) itself changes according to a damped sinusoidal law

where U _m.dop and ƒ _dop is the amplitude and frequency of the additional harmonic signal used in the known invention, and the damped amplitude U _m.ap (t) contains in its structure a detecting sign of the occurrence of a short circuit on the power line.

The theoretical basis of the proposed method is to obtain, at a short circuit on a power line, three voltages u _a.kz (t), u _b.kz (t) and u _c.kz (t) of an input analog electric signal u _in.kz , each of three voltage at short circuit is proportional to the corresponding primary instantaneous value i _A.kz (t), i _B.kz (t) and i _C.kz (t) of the phase short-circuit current:

and, in the general case, each of the phase currents in a transient process consists of an aperiodic component and a forced component, i.e.

and by summing these three voltages, an input analog electric signal u _{input short-circuit} (t) is obtained, in the general case consisting of the sum of two electrical signals, the first of which is the total aperiodic signal u _{∑ a.s. short-circuit} (t), and the second is the total forced signal u _∑.ex.c3 (t), i.e.

in this case, in the general case, the values of the constant coefficients k ₁ , k ₂ and k ₃ in expressions (4) can be different, but ultimately such that, for any type of short circuit, the aperiodic presence in the input signal u input short circuit (t) is _ensured component u _∑.ap.kz (t), which carries information about the occurrence of a transient during short-circuit, in particular, this occurs, for example, when all three coefficients are equal in absolute value, but among which at least one is positive, for example, k ₁ = k, and the other two can be either negative, for example k ₂ = k ₃ = -k, or one of these two of them are positive and the other is negative.

From the input analog electric signal u _in.kz (t) received according to the invention, applied to the input of the selective identifier of the aperiodic component, implemented by the known method of identifying the aperiodic signal, an output sinusoidal electric signal decaying according to the law of the aperiodic function is selected, which has a short circuit on the line conditions of the transition process, the structure corresponding to expression (2), and the presence of this output signal concludes that the presence of Tel'nykh feature associated with the occurrence of any type of short circuit on the power line under overload conditions, and the asynchronous mode oscillation in the system.

A distinctive feature of the proposed method for obtaining a detection sign of faults is that, for example, with interphase faults in a three-phase voltage system, at least one of the phase currents of the transient process will have an aperiodic component of the transient process, since the moment of occurrence of the short circuit is preceded, for example, by a three-phase mode operation of the power line with a load, and when before the occurrence, for example, of a two-phase fault, at least in one of the damaged phases of the line until the fault was not equal zero the instantaneous current value, which will determine the initial conditions for the flow of the aperiodic current of the free process after the occurrence of a short circuit and allow, according to the method, to form a detecting sign of the occurrence of a short circuit in the form of an aperiodic component u _∑.ap.kz (t), which is included in the voltage structure u _input (t) (5), and whose presence is manifested in the appearance at the output identifier damped sinusoidal electrical signal u _O (t), which can be regarded as a data signal, whose appearance in It is possible only in the presence of a mist in the form of feature aperiodic _Σ.ap.kz signal u (t) in the signal _vh.kz u (t).

Under certain conditions, the proposed method can also be used in the formation of an indicative sign of fault by the presence of aperiodic components in phase and linear voltages of a three-phase voltage system. The method can be used both in a system with a grounded neutral and in a system with an isolated neutral.

On figa shows the simplest electrical system with a two-phase short circuit on the communication line W, consisting of:

- two three-phase sinusoidal energy sources E _A and E _B with grounded neutrals and with different but constant frequencies ƒ _A and ƒ _B , and it is accepted ƒ _A > принято _B having internal parameters - active resistances and inductances respectively R _A , L _A and R _B , L _B ;

- a three-phase power line W with parameters R _w and L _w, which performs the function of electrical communication between energy sources.

On the line W shows a two-phase fault between phases A and B and the conditional directions of the currents i _{KZ (A)} and i KZ _(B) to the fault location from the sources E _A and E _B, respectively.

The same figure shows a possible structure of the anti-sway device 1, which fixes the short-circuit processes on the W-line departing from the buses A. To the inputs of the corresponding linear converters 2, 3 and 4, respectively, with constant transmission coefficients k ₁ , k ₂ and k ₃ , for example with transmission coefficients k ₁ = k, k ₂ = -k and k ₃ = -k, secondary currents i _A.kz (t), i _B.kz (t) and i _C.kz (t) from current transformers 5 the corresponding phases A, B and C of the line W. Voltages u _a.kz (t), u _b.kz (t) and u _s.kz (t) from the corresponding outputs of the converters 2, 3 and 4 are supplied to the corresponding three inputs and a three-input adder 6, at the output of which an input voltage u input _{short circuit} (t) is formed, which during short circuit has a structure according to expression (5). This voltage is supplied to the input of the identifier 7 of the aperiodic component of the device operating according to the known invention, the output of which during short circuit on the power line W receives an electric signal in the form of a damped sinusoidal signal u _{output short circuit} (t) with the structure according to expression (2). The presence of this voltage indicates the appearance of a detecting sign in the voltage u _{input short-circuit} (t) (see (5)), which indicates the occurrence of short circuit on the line, and the fact that the voltage u _{output short-circuit} (t) can be used in the operation algorithm , for example, relay protection of the power line W to take measures to ensure the correct functioning of the protection in conditions of overload, swing and asynchronous mode during short circuit.

On figb shows a possible changing relative position of the EMF vectors E _A and E _B when swinging (changing the angle δ (t)), and on figv - changing relative position of these vectors in asynchronous mode, when one of these vectors relative to the other moves in a particular case, with constant slip ω _S :

those. the slip ω _{S is} determined by the frequency difference Δƒ = ƒ _B -ƒ _A respectively EMF E _B and E _A.

The graphs of instantaneous values of electrical quantities shown in Fig. 2 are the result of computer simulation of processes in the simplest grounded neutral system described above, consisting of two three-phase EMF sources E _A and E _B with different frequencies ƒ _A and ƒ _B (fig. 1a) when simulated under the conditions of an asynchronous mode of occurrence of a self-eliminating two-phase fault between phases A and B on a three-phase power line W connecting these sources of electrical energy, moreover, to detect the occurrence of an identifying recognition As for the occurrence of short circuit on the power line, a computer model of identifier 7 of the aperiodic component was used, while the synthesis of this model was based on the well-known method of processing an electrical signal [Patent No. 2331154 (RU)].

Figure 2 shows:

- changes in the instantaneous values of currents i _A (t), i _B (t) and i _C (t), respectively, in phases A, B and C of the power line, current from the source E _A , under asynchronous conditions (ƒ _B > ƒ _A ) with a constant slip ω _S = const before the occurrence of a fault, on the time interval of the existence of a fault (time interval 0 - t ₂ ), namely, the currents i _A.kz (t), i _B.kz (t) and i _C.kz ( t) after self-elimination of short circuit (at t> t ₂ );

- graphs of instantaneous electrical quantities illustrating the change in the input voltage u _in (t) before the occurrence of a short circuit, on the interval of existence of a short circuit and after the self-liquidation of a short circuit, which in the time interval 0 - t _{1 of the} existence of a transient after the occurrence of a short circuit becomes equal to u _{short circuit} (t ) with the structure according to expression (5), while it contains an aperiodic component u _∑.ap.kz (t), the presence of which is a sign of the occurrence of any type of short circuit on the transmission line W.

The same figure shows a graph of the variation of a damped sinusoidal signal u _output.cf (t) with a frequency of ƒ _extra and an aperiodic component appearing at the output of identifier 7 (Fig. 1a), made by the known method of processing an electric signal, and ƒ _extra >> ƒ _A and f _add >> f _B. The time of existence of the electric signal u _{output short-circuit} (t) (time interval 0 - t ₁ in Fig. 2) is associated with the duration of the transition process in a short-circuited circuit, determined by a two-phase short circuit between phases A and B and the source E _A supplied from the side (Fig. .1a, currents i _{ks (A)} ).

From the dependence shown in Fig. 2 for u _{output short-circuit} (t), it follows that in the time interval approximately corresponding to one and a half oscillations with frequency f _A , the envelope of voltage u _{output short-circuit} (t) does not reliably reflect the aperiodic process of the passage of free damped components, currents i _A.kz (t) and i _B.kz (t) entering the structure, but the fact of the appearance of an electric signal u _output.kz (t), functionally related to the presence of an aperiodic component u _∑.ap.kz (t) in the structure electrical signal according to (5), can be used as a revealing sign short circuits on the power line in case of overload, the swing and the asynchronous mode in the power system. The aforementioned inaccuracy of the reflection of the aperiodic process through the envelope of the voltage u _{output short-circuit} (t) in the initial time interval for the appearance of this voltage is explained by the presence of a transient process in identifier 7 of the aperiodic component, with the help of which the fact of the presence of a detecting sign of fault in the signal u _input short-circuit ( t).

The proposed method of obtaining a detecting sign of a short circuit on the power line during overloads, rocking and asynchronous mode in the power system can be implemented using known methods and techniques for processing analog electrical signals used in electronics and techniques for constructing measuring relay protection bodies.

Claims (1)

A method of obtaining a detecting sign of a short circuit on a power line during overload, swing and asynchronous mode in a three-phase alternating current power system, characterized in that an analog electrical signal u _{input short circuit} (t) is formed, which is the sum of three analog electrical signals
u _input (t) = k ₁ · _i.k.z. (t) + k ₂ · i _V.k.z (t) + k ₃ · i _S.k.z (t),
where u _{input circuit protection (} t) is an analog electrical signal; k ₁ , k ₂ , k ₃ - constant coefficients; i _A.kz (t), i _V.kz (t); i _S.kz (t) - phase currents of the line during a short circuit on a three-phase power line, and the constant coefficients k ₁ , k ₂ and k ₃ are chosen such that for all types of short circuits on the line, accompanied by the flow of at least one of the phases short-circuit current line, said analog electrical signal contained in its structure a transient aperiodic component, and the presence in the generated electric signal _vh.kz u (t) the aperiodic component is used as a mist sign by Nali which uw conclude the occurrence of a short circuit in the three-phase power line.

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