RU2807951C1 - Method for determining the short circuit location on tpl with a branch - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: relay protection and automation, used to determine the location of a short circuit to ground on a power transmission line (PTL). The distance to the short circuit location is estimated as the length of the path, during the passage of which the wave of the earth wave channel lags behind the wave of the interphase wave channel by a time equal to the value of the time interval between the moments of arrival from the short circuit location to the installation site of the device of the primary waves of these wave channels. In this case, the value of the mentioned time period is linearly converted by a time counter into a unipolar signal. To do this, the time counter is started at the moment the amplitude discriminator of the interphase wave channel is triggered and stopped at the moment the amplitude discriminator of the earth wave channel is triggered. Moreover, the amplitude discriminator of the earth wave channel is put into operation only when the amplitude discriminator of the interphase wave channel is triggered, and the time counter is reset to zero when its reading reaches the specified value. A TPL section with a short circuit is determined by monitoring a unipolar signal with a comparator with two thresholds, the levels of which are proportional to the time counter readings in case of a short circuit to ground at the beginning and end of the branch. In this case, the TPL sections forming the path that the waves travel from the short circuit location to the installation site of the device are determined according to the short circuit location on TPL. The short circuit location can be determined by assessing two devices installed at the TPL ends. To do this, each device exchanges estimates of the distance to the short circuit location with another device via data channels. The short circuit location is considered to be on the segment between two assessments relating either to one of the TPL sections or to a branch.

EFFECT: increasing the accuracy of estimating the distance to the short circuit location on a main PTL with a branch.

2 cl, 4 dwg

Description

The invention relates to electrical engineering, namely to relay protection and automation, and can be used to determine the location of a short circuit to ground on a power transmission line (PTL).

There is a known method for one-way wave determination of the location of a short circuit (SC) on a power transmission line (US 2015/0081236 A1, publication date: 03/19/2015), according to which, based on measurements of phase electrical quantities at the installation site of the device, a wave signal of the interphase wave channel is formed by using one of the modal transformations and subsequent blocking of the fundamental harmonic. Based on the signal of the waves of the interphase wave channel, the moments of arrival of the primary and the short-circuit waves reflected from the location of the device are recorded and the time interval between them is determined. The distance to the location of a short circuit on a power transmission line is estimated as half the length of the path traveled by the wave of the interphase wave channel during the mentioned period of time.

The method is not able to determine the location of a short circuit on a main power line with a branch. This limitation of the method is due to the configuration of the monitored line. The fact is that when the short circuit is located behind the branch, the wave reflected from the short-circuit location significantly loses its energy due to refractions at the point where the branch is connected and arrives at the installation site of the device greatly weakened.

The need to use a reflected wave is eliminated in the method of one-way wave determination of the location of a fault to the ground (Shalyt G.M. Determination of fault locations in electrical networks. - M.: Energoizdat, 1982, With. 22). The method estimates the distance to the fault location as the length of the path during which the wave of the earth wave channel lags behind the wave of the interphase wave channel by a time equal to the value of the time interval between the moments of arrival from the fault location to the installation site of the device of the primary waves of the mentioned wave channels. To do this, based on measurements of phase electrical quantities at the installation site of the device, wave signals of the phase-to-phase and ground wave channels are generated by applying one of the modal transformations and subsequent blocking of the fundamental harmonic and, on their basis, the moments of arrival of the primary waves from the short-circuit location to the installation site of the device along the phase-to-ground and ground are recorded. wave channels.

Without introducing additional operations and technical measures, the method cannot unambiguously determine the location of the ground fault behind the branch and in the branch itself.

This method is closest to the claimed method in terms of use and technical essence and is adopted as a prototype.

The technical result achieved by the proposed method is to increase the accuracy of estimating the distance to the location of a ground fault on a main power line with a branch.

In the new method, just like in the prototype, based on measurements of phase electrical quantities at the installation site of the device, wave signals of the phase-to-phase and ground wave channels are formed by applying one of the modal transformations and subsequent blocking of the fundamental harmonic. The wave signals of each of the mentioned wave channels are controlled by their amplitude discriminator, the moment of operation of which is taken as the moment of arrival of the primary wave of the wave channel from the short circuit location to the installation site of the device, and the amplitude discriminator is activated when the absolute value of the wave signal exceeds a given threshold. The distance to the short circuit on the power line is estimated as the length of the path during which the wave of the earth wave channel lags behind the wave of the phase-to-phase wave channel by a time equal to the time interval between the moments when the primary waves arrive at the installation site of the device from the short circuit along the mentioned wave channels. At the same time, the speed of propagation of the mentioned waves in the sections of power lines that travel from the location of the short circuit to the installation site of the device is taken into account. The difference of the proposed method is that the value of the mentioned time period is linearly converted by a time counter into a unipolar signal; for this, the time counter is started at the moment the amplitude discriminator of the interphase wave channel is triggered and stopped at the moment the amplitude discriminator of the ground wave channel is triggered. Moreover, the amplitude discriminator of the earth wave channel is put into operation only when the amplitude discriminator of the interphase wave channel is triggered, which ensures the reliability of the method. To detune the amplitude discriminator of the interphase wave channel from false alarms, the time counter is reset to zero when its reading reaches the specified value. By calculation, two levels of a unipolar signal are determined, corresponding to the time counter readings during a ground fault at the beginning and end of the branch, and they are taken as the first and second thresholds of the comparator. A section of a power line with a short circuit is determined by monitoring the level of a unipolar signal with a comparator. If the level of the unipolar signal is below the mentioned first threshold, then the comparator generates at its first output a discrete signal indicating the location of the short circuit on the section of the main power line from the installation site of the device to the branch connection point. Or if the level of the unipolar signal is within the mentioned thresholds, then the comparator generates at its second output a discrete signal indicating the location of the short circuit either on the branch or on the section of the main power line after the branch. Or if the level of the unipolar signal is higher than the mentioned second threshold, then the comparator generates at its third output a discrete signal indicating the location of the short circuit on the section of the main power line after the branch. When estimating the distance to the fault location, the power line sections that form the path that waves travel from the fault location to the device installation location are determined according to the mentioned discrete signals indicating the location of the fault location.

The second implementation of the method is aimed at ensuring unambiguous recognition of a damaged section of a power line. It differs in that the location of the ground fault is determined by estimates of two devices installed at the ends of the main power line. To do this, each device exchanges estimates of the distance to the fault location with another device via data transmission channels and considers that the fault location is located on the segment between two estimates relating either to one of the sections of the main power line or to a branch.

Fig. 1 and fig. 2 explain the operation of the prototype and the proposed method, respectively. In fig. Figure 3 shows a block diagram that implements the proposed method. Fig. 4 illustrates the operating principle of the second implementation of the method.

First, let's look at the operating principle of the prototype. The prototype is designed to determine the distance to the location of a ground fault on a homogeneous power line (Fig. 1).

It is known that at the location of the short circuit, primary waves arise in damaged phases. Each of them is a set of waves of phase-to-phase and ground wave channels (Bickford D.P., Muline N., Reed. D.R. Fundamentals of the theory of overvoltages in electrical networks. Translation from English by V.V. Bazutkina. - M.: Energoizdat , 1981, p. 56). In this case, a wave in the earth wave channel occurs only during a short circuit to the ground.

Interphase wave channel wave (Fig. 1) moves to the installation site of the device at a speed

,

and the wave earth wave channel - with speed

,

Where And , And - specific inductance and capacitance of power lines for direct and zero sequence equivalent circuits, respectively.

It is known that a wave in an interphase wave channel propagates faster than a wave in an earth wave channel, i.e. . Therefore, the primary wave of the interphase wave channel will be at the installation site of the device before the primary wave of the earth wave channel (in Fig. 1 the moments of arrival of the mentioned waves to the device are designated as And ). At the same time, the period of time

on which the wave behind the wave , directly characterizes the distance to the fault location .

It is this property that allows the prototype to estimate the distance to the location of the short circuit on the power line as the length of the path along which the wave of the earth wave channel lags behind the wave of the interphase wave channel by a time equal to the value of the time interval between the moments when the primary waves arrive at the installation site of the device (Fig. 1):

Algorithm (2) works only on a homogeneous power line. Ensuring the functionality of the prototype on a non-uniform main power line with a branch requires localizing the damaged section of the line before determining the distance to the short circuit.

The proposed method does not have this drawback, since it is capable of localizing a section of a power line with a short circuit.

For the proposed method, it is important to determine whether the short circuit can be located on the branch. For this purpose, determine the time intervals by which the wave of the earth wave channel lags behind the wave of the phase-to-phase wave channel, passing the path from the short-circuit location to the installation site of the device when the short-circuit location is located at the beginning and end of the branch (Fig. 2):

And

Formula (4) takes into account that the waves of the phase-to-phase and ground wave channels move along different sections of the line: first along the branch BD with a length with appropriate speeds And , and then - along section AB of the main power line from the point of connection of the branch to the place of installation of the device with a length with speeds And . For convenience of presenting the characteristics of wave motion in different sections of the power line, branch BD in Fig. 2 is shown parallel to the main power transmission line .

The method searches for a section of a power line with a short circuit and estimates its location by comparing a period of time (1) with calculated values (3) and (4).

Let us consider the operation of the proposed method in more detail. A block diagram implementing the method is shown in Fig. 3.

1. The method can work based on measurements of both phase voltages and phase currents at the installation location of the device (in the figures, the installation location of the device is indicated by a flag). For definiteness, we assume that the device measures phase currents , Where - phase designation.

Phase currents at the installation site, the device is converted by linear conversion block 1 into phase-to-phase wave signals and earthen wave channels. To do this, in block 1, intermediate phase-to-phase signals are first generated , and earthen channels according to the rules of one of the modal transformations, for example, Clark:

and then, determining the first difference of readings, they emphasize the wave fronts in them:

Where - reference number;

- designation of the wave channel.

Along with this, the first difference (5) significantly weakens the fundamental harmonic, since the rate of its change on the time scale of wave processes is insignificant. Application of phase-to-phase wave channel signal is not effective for earth faults, and therefore it is not used in the proposed method.

2. The necessary moments of arrival of the primary waves are fixed by monitoring the signals of the phase-to-phase waves and earthen wave channels with amplitude discriminators 2 and 3, respectively. The moment of operation of the amplitude discriminator 2 is taken as the moment arrival of the primary wave of the interphase wave channel, and the moment of operation of the amplitude discriminator 3 - for the moment the arrival of the primary wave of the earth wave channel. Typically, the principle of operation of the amplitude discriminator provides for operation when the absolute value of the channel signal exceeds a given threshold (US 2015/0081236 A1, publication date: 03/19/2015; EO Schweitzer, A. Guzmán, MV Mynam, V. Skendzic, B. Kasztenny and S. Marx , "Locating faults by the traveling waves they launch," 2014 67th Annual Conference for Protective Relay Engineers, College Station, TX, USA, 2014, pp. 95-110, doi: 10.1109/CPRE.2014.6798997).

3. The time of divergence of the primary waves of the interphase and ground wave channels, expressed by the value of the time interval , measured by time counter 4. It is controlled by discrete signals And triggering of amplitude discriminators 2 and 3. Time counter 4 converts the time interval into a unipolar signal . To do this, it is triggered by a discrete signal at the moment the amplitude discriminator of the interphase wave channel 2 is triggered and stopped by a discrete signal at the moment the amplitude discriminator of the earth wave channel 3 is triggered.

The reliability of the method during earth faults is ensured by the fact that the amplitude discriminator of the earth wave channel 3 is put into operation using a discrete response signal amplitude discriminator of the interphase wave channel 2, acting on its input 8. This eliminates its non-selective operation from extraneous waves in the earth wave channel.

In order to reduce the readiness time of the proposed method after possible activations of the amplitude discriminator of the interphase wave channel 2 during interphase short circuits, the time counter is reset to zero when its reading reaches the specified value. The choice of this value is made based on the longest time for which the wave of the earth wave channel lags behind the wave of the phase-to-phase wave channel during a short circuit to ground on a controlled power line.

4. The short circuit can be located on any of three sections of the power line: on the section before the branch, in the branch itself or behind it (in Fig. 2 sections AB , ВD and BC , respectively). In this case, a short circuit in a branch can be observed by the device as a short circuit on a part of the main line after the branch (in Fig. 2 this section is designated as BE ).

The selection of the power line section where the short circuit can be located is performed by comparator 5 by comparing the level of the unipolar signal with two thresholds. The thresholds of the comparator 5 are formed by the threshold setting unit 6 in the form of constant signals with levels And , proportional to time intervals And respectively.

4.1. If less or equal ( less or equal ), then comparator 5 generates a discrete signal at its first output indication of the location of the short circuit on the AB section of the main power line from the installation site of the device to the branch connection point. In this case, the fault location determination unit 7 estimates the distance to the fault location using the classical algorithm (2) taking into account speeds And wave propagation of phase-to-phase and ground wave channels in section AB :

.

4.2. If more and less than or equal to ( more and less than or equal to ), then comparator 5 generates a discrete signal at its second output a sign of the location of the short circuit either on the branch BD or on the section BE of the main power line after the branch.

The case when the device assumes a short circuit in the branchBD, and on the siteBE main power line behind it, illustrated in Fig. 2. The distance to the short circuit on each of them is estimated by the fault location unit 7 taking into account the areaABlength:

And

Where And - the speed of propagation of waves of the phase-to-phase and ground wave channels in the section BE of the main line behind the branch BD .

When estimating the distance to the fault location using formulas (6) and (7), the fault location determination block 7 takes into account the linear relationship between the value and the difference in unipolar signal levels and threshold .

4.3. If more ( more ), then comparator 5 generates a discrete signal at its third output indication of the location of the short circuit on the section of the main power line after the branch connection point. In this case, the ground fault is located in the EC section of the main power line, and the fault location unit 7 estimates the distance to it using (7).

Thus, the method uniquely determines the fault in sections AB and EC of the main power line and produces two estimates when the fault is located on the branch BD or behind it in the section BE of the main power line.

The second implementation of the method makes it possible to unambiguously determine the location of the ground fault by using estimates of the distance to it from two devices installed at the ends of the main power line (Fig. 4). Each device exchanges with another device its estimates of the distance to the fault location via data channels.

Depending on the location of the ground fault, the total number of assessments can be from two to four:

A. If the short circuit is located at either end of the main power line [Fig. 4, a) and b)], then each device determines one estimate of the distance to it ( And ). Both estimates refer to the same section of the line, so all devices consider that the fault is located on the segment between the estimates And .

B. If the short circuit is located near the branch [Fig. 4, c) and d)], then the device on the branch side generates two estimates [in Fig. 4, c) - And , in fig. 4, d) - And ], and the other device - one. Both devices again consider that the fault is located on the segment between two estimates related to the same section of the power line. In fig. 4, c) and d) is the segment between estimates And .

B. If the short circuit is located on the BD branch, then each of the devices gives two estimates ( , And , ). The devices, taking into account that the short circuit is located on the segment between two estimates related to the same section, assume that the short circuit is located on the branch between the estimates And .

Thus, thanks to the localization of the damaged area, it is possible to increase the accuracy of estimating the distance to the location of a ground fault on a main power line with a branch.

Claims (11)

1. A method for determining the location of a short circuit to earth on a main power line with a branch, according to which, based on measurements of phase electrical quantities at the installation site of the device, wave signals of the phase-to-phase and ground wave channels are generated by applying one of the modal transformations and subsequent blocking of the fundamental harmonic, the wave signals of each of the mentioned wave channels are controlled by their amplitude discriminator, the moment of operation of which is taken as the moment of arrival of the primary wave of the wave channel from the short circuit to the installation site of the device, and the amplitude discriminator is activated when the absolute value of the wave signal exceeds a given threshold, estimate the distance to the location of a short circuit on a power line as the length of the path, during the passage of which the wave of the earth wave channel lags behind the wave of the interphase wave channel for a time equal to the value of the time interval between the moments when the primary waves arrive at the installation site of the device from the location of the short circuit along the mentioned wave channels , while taking into account the speed of propagation of the mentioned waves in sections of the power line that travel waves from the place of the short circuit to the installation site of the device, characterized in that the value of the said time period is linearly converted by a time counter into a unipolar signal; for this, the time counter is started at the moment the amplitude discriminator of the interphase wave channel is triggered and stopped at the moment the amplitude discriminator of the earth wave channel is triggered, and the amplitude discriminator of the earth wave channel is put into operation only when the amplitude discriminator is triggered interphase wave channel, and the time counter is reset to zero when its reading reaches the specified value, by calculation, two levels of a unipolar signal are determined, corresponding to the time meter readings during short circuits to ground at the beginning and end of the branch, and take them as the first and second thresholds of the comparator, a section of a power line with a short circuit is determined by monitoring the level of a unipolar signal with a comparator, and if the level of the unipolar signal is below the mentioned first threshold, then the comparator generates at its first output a discrete signal indicating the location of the short circuit on the section of the main power line from the installation site of the device to the branch connection point, or if the level of the unipolar signal is within the mentioned thresholds, then the comparator generates at its second output a discrete signal indicating the location of the short circuit either on the branch or on the section of the main power line after the branch connection point, or if the level of the unipolar signal is higher than the mentioned second threshold, then the comparator generates at its third output a discrete signal indicating the location of the short circuit in the section of the main power transmission line after the branch connection point, in this case, the sections of the power transmission line that form the path that the waves travel from the place of the short circuit to the installation site of the device are determined according to the above-mentioned discrete signals indicating the location of the short circuit. 2. The method according to claim 1, characterized in that the location of a short circuit to ground is determined by estimates of two devices installed at the ends of the main power line, for this purpose, each of the devices exchanges with another device estimates of the distance to the location of the short circuit through data channels and believes that the location of the short circuit is located on the segment between two assessments relating either to one of the sections of the main power transmission line or to a branch.