RU2786506C1 - A method for isolating an overhead power transmission line with a single-phase earth fault in three-phase electrical networks - Google Patents

Abstract

FIELD: The invention relates to the power generation industry and can be used to determine a feeder with a single-phase arc earth fault in branched three-phase overhead electrical networks (EN) with an isolated neutral grounded through an arc-extinguishing coil or a high-resistance resistor.

SUBSTANCE: transient voltages in feeders are recorded by RCL sensors installed in the identical phases in the middle part of each feeder. For this purpose a serial RC circuit is connected to the wire of each feeder, the second terminal of which is connected to the primary winding of a step-down high-frequency transformer, the second terminal of the primary winding of the transformer is grounded. The voltage on the secondary winding is rectified and integrated using an RC circuit. These voltages on all sensors using time synchronization receivers are simultaneously measured by analog-to-digital converters and transmitted via modems to the power supply center, where, after processing the transient phase voltages and confirming the ground fault, the feeder with the highest signal level on the integrating capacitor is determined. A feeder with a maximum voltage is considered a feeder with a ground fault.

EFFECT: reliability and simplicity of determining a feeder with a single-phase earth fault.

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Description

The invention relates to the electric power industry and can be used to determine an overhead power transmission line (OHTL) with a single-phase ground fault in a three-phase electrical network (ES) with an inefficiently grounded neutral, as well as for rough location of a single-phase circuit zone on long VTL.

A known method for determining the feeder with a single-phase arc fault to the ground in radial ES with inefficiently grounded neutral, based on the analysis of the values of higher harmonic components of the zero-sequence current ( I _0v.g. ) in the feeders extending from the power supply center [Gelfand Ya.S. Relay protection of distribution networks. M., 1982] - for example, from the main step-down substation (GPP) or distribution substation (RP). In this method, the selection of a damaged feeder with a single-phase earth fault is carried out by comparing (comparing) the values of high-frequency components in zero-sequence currents (NP): in a damaged connection, the relative content of higher harmonic components I _0v.g. has the maximum value. Due to the fact that this method uses a steady current value as an input measured value, the method is unsuitable for identifying feeders with short-term self-eliminating short circuits, while this information is important for assessing the state of the insulation and targeted preventive testing of lines with weakened insulation, as well as for locating places of single-phase short circuits.

In addition, there is a method for determining the feeder with a single-phase arc fault to the ground in a three-phase ES [L.E. Dudarev, V.V. Zubkov, V.I. Stasenko. Comprehensive ground fault protection. - Power stations, No. 7, 1981], adopted as a prototype and applicable for short-term self-eliminating ground faults, according to which, at the time of breakdown of phase insulation, a zero-sequence transient voltage is recorded on the buses of the power supply center and the first half-waves of high-frequency zero-sequence currents in outgoing feeders. Half-waves of transient voltages and currents determine the initial sign of the direction of power for all feeders. A feeder with a power direction sign opposite to the others is considered damaged.

In this method, depending on the initial sign of the power direction, a threshold device is triggered, leading to the launch of a return device, which, in the absence of stable damage, after a certain delay time Δ t _set , returns the threshold device to its original state. This time Δ t _ass is selected based on the condition of detuning from various kinds of interference (for example, caused by switching in the network or the appearance of higher harmonic components in the voltage) and ranges from 7 to 10 ms. The specified response delay of the return device is determined by the duration of the existence of the zero sequence voltage 3 U ₀ with interference. If the interference is not eliminated within the specified time or reappears at the end of the interval Δ t _ass , leading to the appearance of a voltage 3 U ₀ , then a false alarm occurs (alarm).

In this method, a non-selective (erroneous) determination of the feeder is possible due to the distortion of the phase relationships between current and voltage that occurs at the time of a single-phase ground fault in the wave reflected from the end of the damaged line [Borukhman V.A. On the operation of selective protection against earth faults in 6-10 kV networks and measures to improve them. - Energetik, No. 1, 2000]. Distortions in the voltage wave are also introduced by the measuring electromagnetic voltage transformer due to the rather high frequency spectrum of the wave, reaching tens to hundreds of kilohertz. The frequency characteristics of electromagnetic measuring voltage transformers are such that they are able to transform periodic components only up to a few kilohertz: at higher frequencies, the interturn capacitance of the primary winding affects [Gelfand Ya.S. Relay protection of distribution networks. - M., 1982, p. 294]. In this case, the power sign is incorrectly fixed. By limiting the band of recorded frequencies to increase the selectivity of the selection of a feeder with a ground fault, the scope of this method is significantly reduced , especially for cable electrical networks, in which wave processes are high-frequency due to the small lengths of the lines. To implement both the first method and the prototype method, it is necessary to install zero-sequence current transformers (TTNP) on each feeder. In a number of cases, when the connection of the overhead power line to the busbars of the power supply center occurs without a cable insert, the TTNP needs to be created from three single-phase current transformers, which is a technically difficult task.

An analysis of the above prior art indicates that the objective of the invention is to create a more reliable (reliable) method for determining a feeder with a single-phase unstable arc fault to ground in a power plant, as well as a simpler method that does not require installation on overhead power lines TTNP .

This is achieved by installing sensors of transient electromagnetic processes in the middle part of the feeders on the same phases - linear measurement devices (LMD) (Fig. 1), collecting and processing measurement information. A series R _d -C _d - chain is connected to the phase wire of the feeder, and its second output is connected to the primary winding of a step-down high-frequency (HF) transformer; the second terminal of the primary winding of the transformer is grounded. The output of the midpoint of the secondary winding of the RF transformer is connected to the common wire of the linear measuring device (LUI). The voltage taken from the terminals of the secondary half-windings of the high-frequency transformer is rectified by means of diodes (D) and fed to the integrating R _and -C _and -circuit, and the voltage on the integrating capacitor C _and - to the input of the analog-to-digital converter included in the microcontroller (MK) . With the help of the discharge resistor R _p provide the discharge of the integrating capacitor C _and with the required time constant τ _and . The voltage measured by the ADC in digital form and supplemented by the LUI code number is transmitted to the radio modem. The launch of all ADCs in linear measurement devices is carried out synchronously using PPS signals coming from time synchronization receivers (TSS).

In case of single-phase earth faults, a voltage wave with a steep front from the place of breakdown of the phase insulation propagates throughout the entire ES. It has the highest amplitude and steepness on a feeder with a single-phase earth fault. Running on the RCL circuit, consisting of the elements R _d , C _d and the primary winding of the RF transformer, a signal is formed on the secondary winding, proportional to the steepness and amplitude of the pulse on the damaged or adjacent phase. The voltage on the secondary winding of the HF transformer is rectified, integrated R _and - C _and - by the circuit, simultaneously measured using the ADC and placed in the memory cell of the microcontroller. If this is the instantaneous voltage on the capacitor C _and U _{C, k} ( k is the number of the LUI and the corresponding feeder) exceeds the threshold voltage, i.e. U _{C, k} > U _then. , then with a time delay t _zd unique for each LUI, information about the value of the measured voltage from the memory cell of the MK is fed into the coding unit (BC), adding the LUI code number and the sync code to the digital measurement code. The entire digital combination of codes is broadcast by the radio modem. On the buses of the power supply center, the phase voltages measured by the electromagnetic voltage transformer are fed to the information processing unit (PU) and a single-phase ground fault is recognized. A modem radio receiver is installed in the power supply center. From it, the measurement data from all the LUIs that took part in the measurements are transmitted to the CU, where they are decoded. After establishing the fact of a ground fault, from the total number of measuring signals n received from the radio modem, a signal with the maximum voltage on the integrating capacitor ( U _{C, k} ) is selected, according to which the number of the LMI is determined and, thereby, a feeder with a single-phase ground fault is installed ( damaged feeder).

In FIG. 1 shows a simplified electrical diagram of a device that allows implementing the proposed method for finding a feeder with a single-phase ground fault. In FIG. 2 shows an example of a three-phase (radial) ES with installed LMI, in which the proposed method is implemented. In FIG. 3 shows computer oscillograms of voltages on the integrating capacitors of the LUI and conditional codes generated by the LUI in the case of a single phase-to-earth fault.

The linear measurement device shown in FIG. 1, consists of:RCL-sensor (elements:R _d(one),With _d(2)T _d(3)), diodes D (4), an integrating circuit consisting of a resistorR _and(5) and capacitorC _and (6), discharge resistorR _R (7), a microcontroller (MK - 8) with a built-in analog-to-digital converter (9), a radio modem (RM-10) and a time synchronization receiver (PVS-11).

In the radial ES shown in Fig. 2, electrical energy from the power supply center-1 (for example, from the GPP) is transmitted through feeders (2) to distribution substations (RP - 3) or transformer substations (TP - 4). LUIs (5) are installed in the middle part of each feeder. The power supply center (GPP) is equipped with a radio modem-receiver 6 and an information processing unit (BOI-7), which receives information both from the radio modem and the voltage on the GPP buses, measured by a measuring voltage transformer (TN-8).

The method is carried out as follows.

In the process of a single-phase ground fault on any of the outgoing lines 2 (Fig. 2) on the buses of the GPP (1), by means of the VT (8), the phase voltages are digitally recorded in the PU (7) and the type of damage is recognized - a single-phase short to ground and a damaged phase. As a PU, for example, a monitoring system for transient electromagnetic processes can be used [Kachesov V.E., Larionov V.N., Ovsyannikov A.G. On the results of overvoltage monitoring during single-phase arc ground faults in distribution cable networks. - Electric Stations, No. 8, 2002]. To recognize a single-phase arc fault to earth, various methods are used, for example, for an electrical network whose neutral is earthed through an arc quenching coil, a method is used based on the property of a significantly lower effective voltage on the damaged phase in relation to the voltages on the undamaged phases measured for a limited time interval (~3ms) after the breakdown of the phase insulation and self-extinguishing of the grounding arc [RF Patent No. 2232456 (dated 10/11/2002). A method for recognizing a single-phase arc fault to the ground and a damaged phase in distribution networks with a resonantly grounded neutral // Kachesov V.E./ BI No. 19, 2004]. For electrical networks with an isolated neutral, a method is used, which is based on the property of constant voltage on the neutral of the ES after self-extinguishing of the grounding arc [RF Patent No. 2356062. A method for recognizing a single-phase arc fault to earth and a damaged phase in distribution networks with an isolated neutral / L. V. Bogdasheva, V. E. Kachesov; BI No. 14, 2009].

After establishing the fact of a ground fault, information is processed on the measured voltages on the integrating capacitors C _and (6) in linear measuring devices (Fig. 1). With each breakdown of the phase insulation due to transient electromagnetic oscillations in each RCL sensor on the integrating capacitors C _and (6 - in Fig. 1), a voltage u _{C, k} ( t ) appears (where k is the number of the feeder or the corresponding LUI), which is long (up to several seconds) is stored on their plates. This voltage, shown in Fig. 3 is measured at the moment of arrival of the sync pulse _from the _PVA (according to the PPS signal, _time t _and = u _{C, k} ( t _and ) with the LUI number are transmitted by means of RM (10 - Fig. 1) and RPR (6 - Fig. 2) to the PU (7 - Fig. 2). Information about the magnitude of the measured voltage and the number of a specific LUI MK transmits to the RM with a fixed time delay t _sd relative to the PPS clock unique for each LUI and duration t _inf less than t _sd . Only on one of the LIAs, the time delay is taken close to zero. According to the maximum voltage ( U _{C, k} ) on the integrating capacitor C _and in the PU, a feeder with a single-phase ground fault is determined.

In FIG. 3 shows computer voltage curves on integrating capacitors ( C _and ) after a single single-phase ground fault (at time t _c ) on damaged ( u _C6 ) and undamaged ( u _C1 , u _C5 ) feeders, obtained using the program for calculating transient electromagnetic processes EMTP [HW Dommel, "Digital computer solution of electromagnetic transients in single and multiphase networks," -IEEE Trans., vol. PAS-88, pp. 382-399, April 1969]. The voltage on the integrating capacitor in the linear measurement device on the damaged feeder ( U _C6 ) at the time of measurement t _and exceeds the corresponding voltages on the undamaged feeders (i.e. U _C6 > U _C5 and U _C6 > U _C1 ). The voltage on the integrating capacitor at feeder No. 1 is less than the threshold value ( U _C1 < U _th ), so the measurement information from this feeder (from LIA ₁ ) is not transmitted. After processing the incoming measurement data ( U _C5 , U _C6 ) , the fact of a short circuit at the feeder with LUI ₆ is established in the CU .

Thus, a feeder with a single-phase ground fault in a complex branched air ES is determined by the level of high-frequency oscillations in the RCL sensors installed in the middle part of each feeder. The positive effect of the method is the reliability of the selection of feeders with a ground fault, as well as simplicity, since the installation of a TTNP is not required in the branching nodes of overhead power lines.

Claims (1)

A method for isolating an overhead power line with a single-phase ground fault in three-phase electrical networks, based on the registration of transient voltages by RCL sensors installed on the same phases in the middle part of each feeder; for this, a serial RC circuit is connected to the wire of each feeder, the second output of which is connected to the primary winding of a step-down high-frequency transformer, the second output of the primary winding of the transformer is grounded; the output of the middle point of the secondary winding of the transformer is connected to the common wire of the linear measuring device, and the voltage from the other two outputs of the half-windings of the transformer is rectified by means of diodes and averaged using an integrating RC circuit; the voltage from the capacitor of the integrating RC circuit is supplied to the discharge resistor and to the input of the analog-to-digital converter (ADC) as part of the microcontroller; according to the PPS signal of the time synchronization receivers, the microcontrollers simultaneously start the ADC of all linear measuring devices, if the measured voltage on the integrating capacitor exceeds the threshold value, then the microcontroller with a fixed time delay for each measurement device relative to the PPS synchronization signal starts the radio modem, through which the encoded value of the measured voltage and number of feeder or linear measuring device; a modem radio receiver is installed in the power supply center, phase voltages are measured on the buses of the power supply center by means of a measuring transformer; measurement information from both devices is entered into the information processing unit; the voltage measured on the buses of the power supply center is processed and the fact of a single-phase earth fault is established, after which the data received from the radio modem is analyzed in the information processing unit; from all incoming measurements, a linear measuring device with the highest level of the measured signal is selected, the feeder with such a device is considered damaged, i.e. believe that it has a short circuit to the ground.

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