RU2358368C1 - Three-phase power transmission line connection mode - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the filed of electrical power engineering and is to be implemented in protective relay and automation equipment for control over connection of three-phase power transmission lines (PTL). The proposed mode envisages the sequence of operations being as follows: phase 1 connection, phase 2 and phase 3 voltages measurement, check-up of each of the voltage values measured for being lower than the first reference value; in case the check-up yields positive results one proceeds with phase 2 connection, phase 3 voltage measurement, check-up of the phase 3 voltage value measured for being lower than the second reference value; in case the check-up yields positive results one proceeds with phase 3 connection; in case any check-up yields negative results or there is a protective relay signal for disconnection of the currently connected phase the subsequent phases remain unconnected and the previously connected ones become disconnected. After connection of phase 1 and measurement of phase 2 and phase 3 voltages one additionally performs check-up of each of the voltage values measured for exceeding the third reference value. The first and the second reference values are taken to be equal to 75-85% of the rated phase voltage value; the third reference value is taken to be equal to 5-15% of the rated phase voltage value.

EFFECT: elimination of the risk of interphase fault close-in of a line having all its phases disconnected combined with the mode realisation simplification.

5 cl, 1 dwg

Description

The invention relates to the electric power industry and can be used in relay protection and automation equipment (RPA) to control the inclusion of a three-phase power line (power transmission line), in particular during automatic restart (AR) after an emergency shutdown of power lines or when it is put into operation.

State of the art

Automatic reclosure on power lines is an effective way to increase the reliability of energy systems. Particularly effective is the AR in high and ultra-high voltage power lines. In this case, depending on the type of short circuit (SC) that led to the protection being triggered and the presence of a single-phase reclosure device on the line, the state of the line before starting the reclosure operation may be different (one, two or all three phases are disconnected at one or both ends of the line) . In the event of a two-way emergency shutdown of the three phases of a high or extra-high voltage line, in the vast majority of cases, a three-phase reclosure is performed by simultaneously connecting (with a given time delay, which is set off from the time of arc extinction and deionization of the medium in the fault location) to simultaneously all three phases of the line from one of its ends. If the short circuit on the line by the time of such inclusion is self-removed, then the line is switched on from the other end. The line is being restored. With a stable short circuit (to ground or interphase), the line is disconnected by relay protection immediately after it is connected from one end and connected from the other (opposite) end [1].

From the point of view of the stability of the power system, the main danger is inclusions on interphase faults, especially on close faults, accompanied by a deep decrease in direct sequence voltage [2]. Therefore, the main disadvantage of the simultaneous connection of the three phases of the power transmission line is the high probability of switching on the interphase K.Z. This drawback is so serious that on particularly critical power transmissions, for example, on lines connecting nuclear power plants to the power system, a three-phase automatic reclosure is prohibited.

There is a known method of automatic reclosure of a three-phase power line, in which, after an emergency shutdown of two phases of the line, they are switched on alternately [3]. The method [3] is aimed at avoiding inclusion on interphase faults, and is selected as a prototype. According to the prototype, the voltage on the disconnected phases is preliminarily measured, the correspondence of each measured voltage to the expected voltage induced on the undamaged disconnected phase is checked, and if the test result is positive, the disconnected phase is turned on again, and if the test is negative, the subsequent phases are not turned on, and previously turned on are turned off [3].

With alternating reclosure by the method of [3], it is not always possible to avoid switching the line to interphase faults. This is due to the fact that the method [3] requires the execution (immediately before measuring the voltages of the disconnected phases) of the complex procedure of “unequal and / or simultaneous compensation of capacities” for each of the disconnected phases using shunt and / or compensating reactors, and the ones installed in it verification relationships between measured and expected (control) voltages do not provide reliable and unambiguous conclusions about the presence or absence of short circuits in disconnected phases. This led to the fact that the method [3] did not find practical application on power lines of high and ultra-high voltage, where ARs are especially effective.

Disclosure of the invention

The objective of the invention is to increase the reliability of preventing the inclusion of lines on the interphase fault.

The technical result of the invention is the exclusion of the possibility of connecting the line to the phase-to-phase faults, which are the most difficult for the stability of the power system, and simplification of the implementation of the method. During the implementation of the invention, unsuccessful repeated switching on of any phase (with its subsequent shutdown by protection) can occur only with single-phase short-circuit (i.e., when one phase is shorted to ground), which in most cases is permissible under the conditions of stability of the power system.

The subject of the invention is a method for switching on a three-phase power line, characterized in that the first phase is turned on, the voltages in the second and third phases are measured, the excess of the first control value of each of the measured voltages is checked, and if the test result is positive, the second phase is turned on, the voltage is measured in the third phase, checked exceeding the second control value of the voltage measured in the third phase, and with a positive test result, include the third phase, and with a negative result ltate any of the checks or presence relaying signal for interrupting the phase subsequent phases included did not include, as previously included - disconnect.

The invention has a development consisting in the fact that:

- the first control value is taken equal to 75-85% of the nominal value of the phase voltage;

- the second control value is taken equal to 75-85% of the nominal value of the phase voltage;

- after turning on the first phase and measuring the voltages in the second and third phases, they additionally check that each of the measured voltages exceeds the third control value;

- the third control value is taken equal to 5-15% of the nominal value of the phase voltage.

The development with the introduction of additional verification allows avoiding the inclusion of the second and third phases for single-phase short circuit. In this case, the inclusion of any phase on the short circuit does not occur at all if the first phase has no earth fault.

Other developments allow us to draw reliable conclusions about the presence or absence of interphase and single-phase faults for most existing high and ultra-high voltage lines.

The implementation of the invention in view of its development

The drawing shows a functional diagram illustrating the implementation of the proposed method using measuring and switching equipment power lines.

The drawing shows three phases 1, 2, 3 (phase wires of power lines) located on one side of the power line:

- switches 4, 5, 6, connecting phases 1, 2, 3 to the three-phase bus 7 of the substation;

- measuring transformers 8, 9, 10 voltage connected to phases 1, 2, 3 power lines;

- measuring unit 11, to which the outputs of the transformers 8, 9, 10 are connected;

- analysis unit 12;

- block 13 control switches 4, 5, 6.

The method is as follows.

In the initial state, all three phases of the power transmission line are disconnected, for example, emergencyly according to the relay protection signal (RE), on both sides of the power transmission line. While none of the phases is connected by its switch to the bus 7, there are no voltages induced by other phases on phases 1, 2, and 3.

After a predetermined time from the time of the emergency shutdown, block 13 turns on the phase 4 switch 4, starting the reclosure process. If on phase 1 of the line the short circuit to ground is preserved, then the corresponding signal is supplied to the blocks 13 and 12 from the relay protection and automation system, by which block 13 opens the circuit breaker 4, and block 12 stops the automatic reclosure process.

If on phase 1 there is no earth fault, then the reclosure process continues. Block 11 measures the voltages coming from transformers 9 and 10 (for example, converts them into a digital code), and transmits the measurement results to block 12, which compares each of the measured voltages with a first control value equal to, for example, 80% of the nominal phase value voltage.

If the first control value exceeds each voltage measured in phases 2 and 3, and therefore, only phases induced from phase 1 through interphase capacitors are present in phases 2 and 3, then block 12 determines the absence of phase-to-phase faults of phases 2 and 3 with phase 1 and the AR process continues. If the first control value is exceeded by at least one of the voltages measured in phases 2 and 3, then block 12 generates a signal indicating the presence of a short circuit between the corresponding phase and phase 1. The automatic reclosure process is terminated, and block 13 receives a command to open circuit breaker 4.

After that (in accordance with the development according to claim 4 of the claims), block 12 proceeds to compare the voltages measured in phases 2 and 3 with a third control value equal to, for example, 10% of the nominal value of the phase voltage. If the third control value is exceeded by each of the measured voltages and, therefore, there are voltages induced on the phases 2 and 3 induced through the interphase capacitors from the switched on phase 1, then block 12 establishes the fact that there are no short circuits to the ground of phases 2 and 3. Taking into account the previously made conclusion about in the absence of interphase faults, block 12 generates a signal to turn on switch 5. If the third control value is not exceeded by the voltage measured at least in one of phases 2 or 3, then block 12 determines the presence of a single-phase earth fault etstvuyuschey phase and, acting on the unit 13, the switch 4 switches off and stops the reclosing process.

After turning on the switch 5, the unit 12 re-measures the voltage coming from the transformer 10 connected to the third phase, and compares the measured voltage with the second control value. If the second control value exceeds the voltage measured in the third phase, and therefore, only the voltage induced through the interphase capacitors from the switched on phases 1 and 2 is present in phase 3, then block 12 establishes the fact that there is no short circuit between phases 2, 3 and after a specified time issues to block 13 a command to turn on switch 6. If the second control value does not exceed the voltage measured in the third phase, then block 12 determines the presence of a short circuit between phases 2 and 3. The automatic reclosure process is terminated, and block 13 receives a trip command 4 and 5 switches.

The inclusion of power lines during its commissioning (after completion of construction or repair) by the proposed method is carried out similarly.

As can be seen from the foregoing, the implementation of the invention (including without development according to claim 4 of the claims) allows for any type of damage to prevent the inclusion (connection to the bus 7) of two phases, between which there is a short circuit. This reduces the risk of loss of stability by the power system.

When carrying out the invention, taking into account its development according to claim 4 of the claims, in addition, the inclusion of phases 2 and 3 in the presence of their earth fault is prevented. In this case, only one phase (phase 1, which is turned on first) is connected to bus 7 without checking for the presence of a short circuit on it to the ground. It follows that if the phases of the power transmission lines are connected to the ground with equal probability in two thirds of the cases when the power lines are turned on, the intact phase will be turned on first by the proposed method, and the phase, on which the short circuit to the ground takes place, will not be switched on at all. This reduces the risk of equipment damage.

It can also be seen from the foregoing that, in contrast to [3], the proposed method does not require immediately before the measurement of stresses the procedure of unequal and / or simultaneous compensation of capacitances for each of the disconnected phases (using shunt and compensating reactors) and establishes unambiguous and reliable verification relationships between measured voltages and control values. The ranges of choice of control values, which are given in the clarifying claims, are calculated using the methodology described in [4], confirmed experimentally and are applicable to almost all existing three-phase high and ultra-high voltage power lines.

Information sources

1. Berkovich M.A., Komarov A.N., Semenov V.A. Fundamentals of automation of power systems. M .: Energoizdat, 1981. P. 41-42.

2. Auth. testimonial. USSR No. 843074, IPC Н02Н 3/06. The method of three-phase automatic re-inclusion of the power line and a device for its implementation. BI No. 29, 1981

3. Auth. testimonial. USSR No. 985875, IPC Н02Н 3/06. The way to automatically turn on the power line. BI No. 48, 1982

4. NN Belyakov, KP Kadomskaya, ML Levinshtein and others. Processes with single-phase automatic re-inclusion of high voltage lines. Ed. M.L. Levinshtein. M .: Energoatomizdat, 1991.

Claims (5)

1. The method of switching on a three-phase power line, characterized in that the first phase is turned on, the voltages in the second and third phases are measured, the excess of the first control value of each of the measured voltages is checked and, if the test result is positive, the second phase is turned on, the voltage in the third phase is measured, the excess is checked the second control value of the voltage measured in the third phase, and if the test result is positive, the third phase is turned on, and if the test result is negative, either If the relay protection signal turns off the on phase, the subsequent phases do not turn on, and the previously turned on phases turn off. 2. The method according to claim 1, characterized in that the first control value is taken equal to 75-85% of the nominal value of the phase voltage. 3. The method according to claim 1, characterized in that the second control value is taken equal to 75-85% of the nominal value of the phase voltage. 4. The method according to claim 1, characterized in that after turning on the first phase and measuring the voltages in the second and third phases, the excess of each of the measured voltages of the third control value is additionally checked. 5. The method according to claim 4, characterized in that the third control value is taken equal to 5-15% of the nominal value of the phase voltage.