RU2343617C1 - Method for combined inhibit of automatic switchover for permanent faults and voltage falls - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: application: in electric systems automation. The method consists in the following: at the moment of loss of voltage in section, presence of SCC (short-circuit current) is registered at input of feed transformer and after switching it off, linear voltage absence is registered which fact is caused by input switch cutoff; no-current condition time till "АПВ" is counted and if at the moment of count cancellation SCC appears again then the conclusion is made that there is permanent fault in substation buses between input switch and AS (automatic switchover) switch and AS inhibition signal is generated. Otherwise connected emergency load power is compared with backup system power whereupon conclusion is made if backup source has sufficient additional load capacity to connect failing section of main source system without voltage fall and when reserve is not sufficient the AS inhibition signal is set.

EFFECT: application field and functionality enhancement.

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Description

The invention relates to the automation of electrical networks and is aimed at the combined prohibition of the automatic switching on of the reserve (ATS) for stable short circuits (KZ) and voltage dips on bus sections of two-transformer step-down substations to prevent the spread of an unresolved short circuit in distribution networks with two-way power and limiting the frequency of voltage dips.

In existing power supply systems, equipment and current-carrying elements are usually designed only for rated currents. When the voltage disappears due to a short circuit on the substation's tires, an ABP is applied. Its circuit breaker trips and trips with acceleration. However, turning on the device to an unrepaired short circuit leads to undesirable consequences. In this case, the sectional switch, power transformer and other electrical equipment of the backup system are subjected to significant thermal and dynamic effects. In addition, the load connection can be accompanied by significant power surges if the backup system does not have sufficient reserves, which will necessarily cause a power failure and an avalanche of accidents.

There is a method of prohibiting substation automatic turning on of the reserve for a stable short circuit, which consists in fixing the short circuit current at the input of the supply transformer between the input switch and the ABP switch, after its disappearance, the time of a non-current pause of the automatic restart (AR) of the input switch is counted and, if at the end of the countdown, the short circuit current does not disappear, a signal is issued to prohibit the operation of the section switch ABP [1].

The disadvantage of this method is that it does not take into account possible emergency conditions caused by unacceptable load surges of the bus system connected to the backup input, during which voltage dips occur in the system both on the side of the emergency section of the network and on the backup section, which leads to violations in power supply. The proposed method provides for limiting the frequency of voltage dips and their dynamics in combination with preventing the spread of a stable short circuit to undamaged sections of the network. The implementation of the method does not require structural changes in the topology of the existing power supply systems and equipment replacement.

The objective of the invention is to expand the scope and functionality of the method by using it to prohibit automatically turning on the backup power to voltage dips on the buses of step-down substations in the presence of an automatic reclosure input circuit breaker, as well as minimizing the frequency, limiting the dynamics of the development of voltage dips in the power supply system.

The method of combined prohibition of automatic inclusion of a reserve (ATS) for stable short circuits (SC) and voltage dips (PN) consists in comparing four parameters characterizing the operating modes of electrical equipment. The method is characterized in that one of them is a dead time pause before the automatic restart (AR) of the input switch. As a second parameter, take the time between the appearance of a short circuit current at the input of the supply transformer from the low voltage side to the input switch of the two-transformer substation. It is compared with the first parameter, for which, at the time of the disappearance of voltage on the sections, the presence of a short circuit current at the input of the supply transformer is recorded. After it is turned off, the absence of line voltage due to the disconnection of the input switch is recorded, the time of a dead time pause to reclose is counted. If a short circuit current appears again at the time of the countdown, then a conclusion is drawn that a stable short circuit has occurred on the substation buses between the input switch and the ABP switch. In this case, an ATS prohibition signal is sent. Otherwise, when the short circuit current is absent at the time of the countdown, the following two state parameters are compared, one of which takes the power of the connected emergency load, and the other the power of the backup system. After that, they conclude that the additional load capacity of the backup input is sufficient to connect the emergency section of the main source network without voltage failure and, when there is not enough reserve, they signal to block the ATS.

The drawing shows a diagram of the combined prohibition of ABP for stable short circuits and voltage dips.

The ban scheme contains two independent inputs No. 1 and No. 2 operating in parallel (elements 1 and 2), supply transformers 1T and 2T (elements 3 and 4), an input switch for input No. 1 Q ₂ (element 5), an input switch for input No. 2 Q ₄ (element 6), bus sections I and II (elements 7 and 8), section switch ABP Q ₇ (element 9), load switches on the outgoing lines (elements 10, 11, 12, 13), voltage control units for bus sections (BKN1 and BKN2, elements 14 and 15), current control blocks for each input (BKT1 and BKT2, elements 16 and 17), power control units of the allocated load for each volvo yes (BKM1 and BKM2, elements 18 and 19), power reserve control units of the connected source of bus sections (BKR1 and BKR2, elements 20 and 21), data comparison link (ZSD, element 22), parameter processing device (UOP, element 23) .

The scheme works as follows. In normal mode, an operating current flows at the inputs of transformers 1T, 2T (elements 3, 4) and busbar sections I, II (elements 7, 8). Since the currents on the bus sections are not equal to the short circuit current (short circuit), the entire system of control units is not subjected to signals from the relay protection of the input switches Q ₂ or Q ₄ (elements 5 and 6), which are equipped with an automatic reclosing device (AR), as a result, the circuit does not start.

In the event of a short circuit in the section of the busbar section I behind switch Q ₂ (element 5), the protection puts it out of operation. At this point in time, the BKT1 (element 14) detects a significant increase in current in the main source system, and then gives a signal of the form I _lat.I → ∞ to the OPS (element 23). At the same time, BKN1 detects the disappearance (or a multiple decrease) of linear voltages in section I (element 7) and sends a signal of the form U _lat.I → 0 to _UOP (element 23). After a predetermined time delay, the protection turns off the Q ₂ apparatus (element 5), equipped with an automatic reclosing device (AR). Short circuit current and line voltages on buses of section I disappear. These events are recorded by the corresponding blocks BKN1 and BKT1 (elements 14 and 16), which form teams of the form I _lat.I → 0 and U _lat.I → 0 on UOP (element 23), where a secondary analysis of the incoming from the blocks is carried out information. Then, the circuit breaker is automatically turned on again (element 5) with the set shutter speed t of _{reclosure (Q2)} . RPS (element 23) produces a delay in time t _RPS equal to the dead time of the reclosure: t _RPS = t _{reclosure (Q2)} , which coincides with the moment of receipt of the secondary signals from blocks BKN1 and BKT1 (elements 14 and 16). By virtue of which, the OPS generates and sends a command to prohibit the ATS and Q ₇ operation (element 9). When normal operation is restored, voltage will appear on the busbar section I, which will be recorded by the executive bodies and the logical part of the ATS, and the circuit will return to its original state.

In case of an unstable short circuit of secondary signals from blocks BKN1 and BKT1 (elements 14 and 16) it does not arrive at the OPS (element 23), therefore, an involuntary time delay is not performed. At this moment, the BKM1 block (element 18) fixes the value of power at the allocated load and gives this value to the WHSD (element 22) in the form P _working.s.I = m _I. At the same time, the BKR2 block (element 21) determines the power reserve in the standby system and then gives the command P _res.s.II. = n _II to the data comparison link (element 22), where the check of compliance with the power levels at load nodes is implemented : m _I ≈n _II . When the reserve is not enough to connect the emergency section of the network without voltage surge, the ZSD will send a command to the parameter processing device in the form of a signal: m ₁ >> n _II , which indicates the danger of a voltage dip.

Then the OPS (element 23) produces a delay in time t _OPS equal to the dead time of the reclosure: t _ROP = t _{reclosure (Q2)} , which coincides with the moment of receipt of the signal from the link comparison data. Therefore, the parameter processing device generates and gives a command to prohibit ATS and Q ₇ operation (element 9). When normal mode is restored, voltage will appear on the busbar section I (element 7) and the circuit will return to its original state.

The proposed method for the combined prohibition of ATS for stable short circuits and voltage dips was tested under production conditions at a step-down substation 110/10/6 kV of JSC Lipetskenergo. The experiment confirmed the correctness of the method and the relevance of its implementation and made it possible to determine the size of the dips depending on the distance of the load nodes from the power source.

Thus, a ban on turning on an ABP sectional switch at a two-transformer substation is only granted if there is a stable short circuit on one of the bus sections and when it is transient, but the backup system does not have sufficient power reserves to cover power surges of nodes connected in emergency mode load, which prevents the inclusion of ATS on voltage dips. The prohibition method is applicable for ABP means of both single and double acting, moreover, the principle of operation of control units does not change.

Literature

1. Pat. 2173017 Russian Federation, IPC Н02J 9/06, 13/00. The method of prohibiting the automatic inclusion of a reserve for a stable three-phase short circuit on the substation tires [Text] / Vasiliev V.G .; Applicant and patent holder Oryol State Agrarian University. - No.2000105132 / 09; declared 03/01/2000. - 6 p.

Claims (1)

A method of combined prohibition of automatic inclusion of a reserve (ATS) for stable short circuits (CI) and voltage dips (PN), which consists in comparing four parameters characterizing the operating modes of electrical equipment, characterized in that one of them is the time of a dead time before automatic restart ( AR) at the input switch, as a second parameter, take the time between the appearance of the short circuit current at the input of the supply transformer from the low voltage side to the input off the two-transformer substation and compare it with the first parameter, for which, at the time of the disappearance of voltage on the section, the presence of a short circuit current at the input of the supply transformer is recorded, and after its disconnection, the absence of line voltage due to the disconnection of the input switch is recorded, the time of a dead time before the reclosure is counted, and if at the time of the countdown the short-circuit current appears again, then it is concluded that a stable short circuit has occurred on the substation buses between the input ATS circuit breaker and switch, in which case an ATS inhibit signal is output, otherwise, when there is no short circuit current at the moment of counting stop, the following two state parameters are compared, one of which takes the power of the emergency load to be connected, and the other the backup power systems, after which they conclude that the additional load capacity of the backup input is sufficient to connect the emergency section of the main source network without voltage failure and, when the reserve is under atochno fed signal to ban the ATS.