Method of finding feeder with single-phase arc fault to ground in radial distribution cable circuits

FIELD: electrical power engineering.

SUBSTANCE: method can be used for finding feeder with single-phase arc fault to ground in radial distribution cable circuits of 6-10 kV having isolated and resonant-compensated neutral conductor or with neutral conductor earthed through high-ohmic resistor. Transient voltages at buses of main point are registered in single-phase shorting as well as first half-waves of transient currents in feeders coming from the buses. Polarities of currents are juxtaposed. Feeder having current polarity being opposite to the others is supposed to be damaged. In this case shorting mode is recognized on the base of analysis of phase voltages at buses of main supply point. After that the polarities of first half-waves of transient currents being registered in conductors connecting envelopes of cables with grounding mat have to be compared.

EFFECT: improved reliability.

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The present invention relates to power engineering and can be used to identify feeder (supply line) with single-phase arc circuit (LDU) of land in the radial distribution cable networks 6-10 kV with the isolated resonance offset or earthed through a high impedance resistor neutral.

There is a method of determining feeder with single-phase arc earth fault in the radial distribution cable networks, based on the analysis of the steady-state values of higher harmonic components of the current zero-sequence (I_SVG) [1]. In this way the selection is invalid feeder by matching (comparison) value of high-frequency currents in the damaged and undamaged connections: invalid accession I_SVGhas the maximum value.

Because in this way as an input the measured value is used steady-state current value, it is unsuitable for selection of feeders with short-term samoustraniajutsia closures, while this information is important for assessing the insulation condition and targeted preventive testing lines with poor insulation.

In addition, there is a method of determining feeder with single-phase arc loan is a W on the earth in the distribution cable networks [2], adopted as a prototype and is applicable for short samoustraniajutsia circuits, according to which the time of injury register transient zero-sequence voltage and the first half-wave high-frequency zero-sequence currents in the outgoing feeders. Voltage and current determine the initial sign of power direction for all feeders. Feeder, having a sign of power direction (determined by the polarity of the current), the opposite of the other, is made invalid.

In this way depending on the initial sign of power direction trigger threshold device, leading to the launch device of return, which in the absence of sustained damage after some time t_ZVreturns the threshold device to its original state. This time t_ZVchosen from the terms of the detuning from the various types of interference (for example, caused by switching in the network or the appearance of higher harmonics in the voltage and ranges from 7 to 10 MS. This delay device of return is determined by the duration of the voltage zero-sequence 3U₀when interference. If the nuisance within a specified time persists or recurs at the end of the interval t_ZV, resulting in a tense which I 3U ₀, there is a false alarm (alarm).

In this way it is possible selective determination of the feeder due to the distortion of the phase relation between the current and the voltage arising at the time of single-phase earth fault in a mirrored from the end of the damaged line wave [3]. Distortion in wave voltage also makes the measurement of electromagnetic voltage transformer from the high frequency spectrum of the waves, reaching tens or hundreds of kilohertz. The frequency characteristics of voltage transformers are such that they are able to transform periodic components only up to a few kHz: at higher frequencies affects inter-turn capacitance of the primary winding [1, str]. Properly fixed the sign of power. Limiting the bandwidth of the recorded frequencies for improving the selectivity of the selection of the feeder with circuit significantly reduces the scope of application of this method, especially for cable networks, in which the high-frequency wave processes because of the small lengths of the lines.

Analysis of the above prior art suggests that the object of the invention is the creation of a more reliable detection method feeder with single-phase arc circuit in radial distribution cable networks.

This is achieved by the fact that h is of the known method of allocation invalid feeder register transient voltage at the busbars of the main food item and the first half-wave transient currents in the outgoing feeders and compare the polarity of the currents; feeder, with the polarity of the current is opposite with respect to the other, is damaged, first perform the recognition mode of the circuit, analyzing the phase voltage at the busbars of the main food item, then compare the polarity of the first half-wave transient currents recorded in the conductors connecting the sheath of the cable with the grounding of the substation.

Figure 1 shows a fragment of the radial cable network that implements the proposed method; figure 2 is the waveform of the phase voltage (kV) [4] and their derivatives (kV/s) when the LDU real cable network 10 kV with insulated neutral; figure 3 - calculated waveforms of phase currents and current in a conductor connecting the sheath of the cable with the grounding of the substation; figure 4 - currents in the membranes of intact and damaged feeders and appropriate logic voltage.

In radial cable network (figure 1) energy from the main food item (GPP) - step-down substation 1 is transmitted via cable lines 2 to distribution (SPM), transformer substations (TS) or the load. In the network nodes (GPP, ER) on the conductors connecting the shell with the ground loop with a ground resistance R_C3, installed insatiable (subanalyses) the current transformers 4, which is loaded on the resistance is agrusti 5.

The method is as follows.

In the process of single-phase earth fault on any of the outgoing lines 2 (figure 1) on the tires of the main food item (node power) 1 fixed phase voltage (which can be used monitoring system surge [4, 5]), and recognize the kind of damage - single-phase earth fault. Stress measurement performed on the tire main food item using a capacitive voltage dividers [4], without introducing distortions in the measured values up to hundreds of kilohertz. For recognition of single-phase arc earth fault can be used a variety of methods, for example, using artificial intelligence systems [6], when on the basis of experimental (or obtained by the numerical simulation) waveforms of various faults in the electrical network is formed and trained artificial neural network (Ann)that produce a particular kind of damage on the real waveforms of phase voltages of the transition process, represented in digital form. To recognize the LDU can also be used techniques, consisting in the analysis of the characteristic features of the type of damage that is implemented, for example, for a resonant compensated networks method [7, 8], which uses matching polarities (characters) derivatives of the phase voltage is response (u _γat the time earth fault when exceeding the derivative (in absolute values) to some point (U_mouth), for example, the doubled value of the maximum of the derivative of a linear voltage u_landγ={A, B, C}) with subsequent determination of the effective value of integration for a limited timeor for voltage, represented as a numeric array, integrating by rule rectanglesthe sampling time, n is the number of samples per integration time t_and≅2 msec): when the ground fault current voltage on the damaged phase several times (depending on the degree of phase compensation network capacity) is less than intact.

For networks with isolated or earthed through a high impedance resistor neutral in addition to Ann for pattern recognition can be used previously specified characteristic matches the signs of the derivatives of the phase voltages in combination with the calculation of at least two triads unipolar pulse phase derivative over time of the order of 12-15 MS (figure 2).

After detection of the ground fault by any of the above methods produce damaged the ider, using the property of the opposite polarities of the first half-wave of high frequency currents measured in the conductors, grounding sheath of the cables in substations. This property is analogous to the principle of opposite polarities zero-sequence currents [2].

First time earth fault transient current zero-sequence, leaking from the side of main food item, and the current in the shell (i_about), which is connected with the grounding of the substation consist mainly of the discharge current phase capacity. Figure 3 shows the calculated waveforms obtained by [9], with the closure phase "C" in the radial network, consisting of five cables of different lengths (0,5; 1; 2; 3 and 4 kms), from which it is clear that high-frequency transient currents intact phases (i_A, i_B) are not comparable in value with the current of the faulted phase (i.e. i_C>>i_Aand g i_C>>i_B), and the current in the shell is opposite in polarity and similar in amplitude and shape to the current of the faulted phase (and current 3i₀).

The current flowing through the shell of the damaged cable, has the opposite direction with respect to the currents undamaged cables (figure 4). High frequency currents in the circuit (the first oscillation) is measured in the conductors connecting the cable sheathing with Comte who Ohm grounding substation using high-frequency insatiable current transformers, for example, transformers with a ferrite magnetic and non-magnetic gap. As such, for example, you can use single-turn transformer (with one revolution of the measuring current window magnetic)performed on the U-shaped ferrite magnetic core (brand MN) section ˜4 cm²with non-magnetic gap of the order of 5 mm and a secondary winding, containing several hundreds of turns and is loaded by a resistor of the order of tenths of ohms. By the first half-wave currents, giving the load current transformers voltage drop, with the help of simple electronic devices easily formed logical voltage, the polarity of which is easily detected invalid feeder (figure 4).

Thus, the definition of the feeder with single-phase arc circuit in radial distribution cable networks is performed on the basis of reliable facts earth fault, determined on the basis of the analysis of the recorded phase voltages of the network, and determine the damaged feeder on the polarity of the first half-wave current in a conductor connecting the cable sheath, with the grounding of the substation.

List of used sources

1. Gelfand AS relay protection of distribution networks. M., 1982.

2. Laidudele, SUV, Whistance. Comprehensive protection against short circuits on the earth.- Electric station, No. 7, 1981.

3. Brahman VA On the operation of the selective protection against short circuits to earth networks 6-10 kV and measures for their improvement. - Energetic, No. 1, 2000.

4. Kutasov V.E., Larionov V., Ovsyannikov A.G. ON the results of monitoring the surge in single-phase arcing fault to ground in the distribution cable networks. - Electric station, No. 8, 2002.

5. Detection and monitoring of cable networks medium voltage / Kadom C.P., Kutasov V.E., Lavrov Y.A. and other - Electrical engineering, No. 11, 2000.

6. A Fault Classification Method by RBF Neural Network With OLS Learning Procedure / Whei-Min Lin, Chin-Der Yang, Jia-Hong, Ming-Tong Tsaj. - IEEE Trans. on Power Delivery, Vol. 16, No. 4, Oct., 2001, pp.473-477.

7. Kutasov V.E., Lavrov Y.A., Ovsyannikov A.G. V. Larionov., Pavlikov CU ON monitoring of distribution networks / Proceedings of the Second all-Russian scientific and technical. proc. "Limitation of overvoltage and modes of neutral grounding networks 6-35 kV", Novosibirsk, NSTU, October 15-17, 2002.

8. Monitoring overvoltages in underground HV cable distribution networks / V.Dikoy, V.Kachesov, A.Ovsyannikov, V.Larionov. - CIGRE, 39^thSession 2002, 21-103.

9. The Electromagnetic Transients Program (EMTP). Rule Book 1, 2. DCG/EPRI, 1996.

The detection method feeder with single-phase arc earth fault in the radial distribution cable networks, based on the fact that in the regime of single-phase earth fault register transient voltage at the busbars of the main food item and the first Polow the wave transient currents in the outgoing feeders, match the polarity of the currents, the feeder having the polarity of the current is opposite with respect to the other, is considered invalid, characterized in that the first perform the recognition mode of the circuit, analyzing the phase voltage at the busbars of the main food item, then compare the polarity of the first half-wave transient currents recorded in the conductors connecting the sheath of the cable with the grounding of the substation.