JPH04364325A - Overload protective system for loop transmission system - Google Patents

Abstract

PURPOSE:To protect a loop transmission line against overload by tripping a feed out circuit breaker for the loop transmission line on the side where power flow is fed out in the direction of bus, based on the logical product of operations of a power flow detecting relay and an overcurrent detecting relay. CONSTITUTION:Upon stoppage of one bank, e.g. bank #1U, a circuit breaker CB2 or CB3 is interrupted and a power flow a is generated in the direction of B1, for example, to cause overload of a loop transmission line LS. The power flow a' is detected through a power flow detecting relay 191P and overcurrent of the transmission line is detected through an overcurrent detector 157 in order to produce a logical product for tripping a circuit breaker CB7. Loads L1, L2 are thereby disconnected from the loop transmission line thus protecting the loop transmission line. Upon function of any one of an undervoltage relay 127 or a ground overvoltage relay 164, the circuit breaker CB7 is blocked from being tripped thus preventing unnecessary function at the time of external fault.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides overload protection when a loop transmission line drawn out from a substation connected to a different bus line is used as a substitute for a bus interconnection line. Regarding the method.

0002

[Prior Art] Conventionally, loop power lines have been used in unit substations with a substation configuration as shown in Figure 3(a) and dual main bus substations with a busbar configuration as shown in Figure 3(b). When installed, it has two sending circuit breakers due to its shape, so the circuit breaker on the bus line opens and the sending circuit breaker opens on the bank #.
There may be a situation in which the circuit breaker in 1U, #2U, or the bus tie is opened and the sending circuit breaker is divided into A and B. This state is called a different bus configuration.

Taking a unit substation as an example, a substation with a different bus loop configuration has banks #1U and #1, as shown in FIG.
Bus lines B1 and B2 of 2U are connected by a bus link B12 via circuit breakers CB2 and CB3, and a loop power transmission line LS is connected to the bus lines B1 and B2 via circuit breakers CB7 and CB8.

0004

[Problems to be Solved by the Invention] In the above-mentioned different bus loop configuration, if, for example, the circuit breaker CB1 of bank #1U is opened to stop the power supply from bank #1U, the load connected to the bus B1 side Power is supplied to L1, L2, etc. via the bus connection line B12. In this case, an accident F1 occurs in the bus line B12, and the circuit breaker CB2 or CB3
When the is opened, loads L1 and L2 are transferred via the bus connection B12.
The power flow a that was being supplied to the loop power line L as shown by a'
It flows from the working bank #2U to the stopped bank #1U via S.

[0005] In such a case, since the allowable current of the loop power line LS is usually smaller than that of the bus line B12, there is a possibility that the loop power line LS will be overloaded depending on the magnitude of the flowing current. .

However, the conventional loop power transmission system protection system does not have a built-in relay that can detect this overload condition, so in some cases, the overload may cause a malfunction in the loop power line, resulting in the interruption of power supply to consumers. There was a risk of inviting

The present invention has been made in view of the above-mentioned problems in the prior art, and its purpose is to stop one bank and open the bus circuit breaker in a different bus loop configuration. An object of the present invention is to provide an overload protection system in a loop system that can prevent overload on a loop power transmission line without stopping the power supply to loop consumers.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the loop power transmission line overload protection system of the present invention is as follows:
In a loop power transmission system in which loop power transmission circuit breakers are connected to different buses, a power flow detection relay detects the power flowing to the bus through the loop power line, and detects overcurrent in the loop power line. An overcurrent detection relay is provided, and the output circuit breaker of the loop transmission line on the side where the power flow is flowing toward the busbar is tripped by the logical product of the operations of the power flow detection relay and the overcurrent detection relay.

[0009] Furthermore, tripping of the circuit breaker is achieved by providing a fail-safe overcurrent detector that detects that the power flow flowing out to the busbar side is an overcurrent state for the loop transmission line;
It is preferable to operate by logical product with the operation of this fail-safe overcurrent relay.

Furthermore, the outputs of the undervoltage relay, which operates due to a drop in bus voltage, and the earth fault overvoltage relay, which operates due to the zero-sequence voltage of the bus, are included in the trip conditions of the circuit breaker, and the circuit breaker is tripped only when both of the relays are inoperative. It is possible.

[0011]

[Operation] In a loop power transmission system that is interconnected with different buses connected by bus lines, when one bank stops and the bus line connecting the buses is cut off, from the other operating bank Power flows through the loop transmission line to the load connected to the stop bank side bus bar.

[0012] The power flow detection relay detects the power flow flowing out to this bus bar. The overcurrent detection relay also detects overload on the loop transmission line. Therefore, by tripping the send-out breaker of the loop transmission line on the side where the power flow is flowing toward the bus bar by the logical product of the operations of the power flow detection relay and the overcurrent detection relay, the stop bank side bus bar can be disconnected from the loop transmission line. The loop power transmission line can be prevented from being overloaded due to the power flow.

[0013] Furthermore, a fail-safe over-current detector is provided to detect that the power flow flowing out to the busbar side is an over-current state for the loop transmission line, and the operation of the circuit breaker is controlled by this fail-safe over-current detector. By using the logical product of

Furthermore, if either the undervoltage relay or the ground fault overvoltage relay operates, the trip of the circuit breaker is locked, thereby preventing unnecessary operation in the event of an accident.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described with reference to the drawings. Note that the same components in FIG. 1 as those conventionally shown in FIG.

In FIGS. 1 and 2, CT1 and CT2 are instrument transformers (hereinafter simply referred to as CT1 and CT2), 191
P, 291P is the bus line B1 connected to CT1, CT2,
Power flow detection relay that detects power flow in the B2 direction, 157,2
57 is an overcurrent detection relay connected to CT1 and CT2,
157F and 257 are fail-safe overcurrent detection relays connected to CT1 and CT2.

When bank #1U is stopped and bus breaker CB2 or CB3 is opened, the power flow a' is the load L4 of the loop transmission line LS.
, L3, so the largest one is C
This is detected at T2. Furthermore, the current in the direction of bus line B1 can be detected by CT1.

Therefore, in order to interrupt the power flow in the bus B1 direction, as shown in FIGS. 11, the output of this AND circuit 11 is added to the timer T1, and when the output of the AND circuit 11 continues for a predetermined period of time, the output of the timer T1 trips the circuit breaker CB7.

However, simply observing the overcurrent at the overcurrent relay 257 on the CT2 side does not necessarily mean that a large current is flowing toward the bus B1 side. Therefore, if the output of the timer T1 and the output of the fail-safe overcurrent relay 157F on the CT1 side are input to the AND circuit 12, and the output of the AND circuit 12 is used to trip the sending circuit breaker CB7, the loop Overloads on power transmission lines can be detected reliably.

Similarly, the power flow detector 291P on the CT2 side, the fail-safe overcurrent relay 257F, and the overcurrent relay 157 on the CT1 side are connected as shown in FIGS. 2(a) and (b) to detect the power flow a' Loop transmission line L due to power flow in the opposite direction
S overload protection.

In FIG. 2(a), the overcurrent relay 257,
The outputs of the overcurrent relays 157 and 157 are input to the AND circuits 11 and 21, respectively, as shown in FIG. 2(b).
The output of 257 may be input to the OR circuit 1, and this output may be input to the AND circuits 11 and 21.

[0022] In the loop transmission line overload protection system, which is composed of a combination of the outputs of the power flow detection relay, overcurrent detection relay, and fail-safe overcurrent relay described above, it is possible to prevent short circuits and ground faults in the feeders connected to the busbar. If this occurs, depending on the magnitude of the fault current passing through the loop transmission line, there is a risk that the loop transmission line's sending circuit breaker may trip, causing a malfunction. The overload protection method of the present invention is as follows:
The purpose of this relay is to protect the loop transmission line from overload, which has become a substitute for the bus interconnection line, and it is not desirable to activate it in response to an external accident.Protection against external accidents should be left to the protection relay for the accident countermeasure. It is.

Therefore, the undervoltage relay 127 operates due to a drop in bus bar voltage due to a short circuit accident occurring in the feeder.
227 and the output signals of the ground fault overvoltage relays 164 and 264, which are operated by the zero-sequence voltage appearing on the bus line due to a ground fault accident, are input to the OR circuit 13 or 23, respectively, and the negative signal of the output is input to the AND circuit 11 or 21. If either the undervoltage relay 127 or the ground fault overvoltage relay 164 or the undervoltage relay 227 or the ground fault overvoltage relay 264 operates,
The trip signal to the sending circuit breaker CB7 or CB8 is locked. In other words, it is assumed that the undervoltage relay 127 and the ground fault overvoltage relay 164 or the undervoltage relay 227 and the ground fault overvoltage relay 264 are respectively only in the inoperable state and can trip the circuit breaker CB7 or CB8, thereby preventing unnecessary operation in the event of an accident. We are trying to prevent this.

[0024]

[Effects of the Invention] Since the present invention is configured as described above, it protects the loop power transmission line from overload caused by the current flowing through the loop power transmission line to the bus on the stop bank side, and the loop power transmission system is delivered to the consumers of the loop power transmission system. It is possible to prevent the power supply from being stopped.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram of an overload protection system in a loop power transmission system according to an embodiment of the present invention.

FIGS. 2(a) and 2(b) are sequence circuit diagrams of overload protection systems, respectively.

FIGS. 3A and 3B are circuit diagrams showing the configurations of a unit substation and a dual main bus substation, respectively.

FIG. 4 is an explanatory diagram of a conventional different bus loop power transmission system.

[Explanation of symbols]

#1U, #2U... Bank, P01, P02... Power supply, CB
1 to CB8...Blocker, B1 to B4...Bus bar, B12...Bus connection line, LS...Loop transmission line, L1 to L5...Load, 191P
, 291P...Power flow detection relay, 157,257 Overcurrent relay, 157F, 257F...Fail-safe overcurrent relay, 127,227...Undervoltage relay, 164,26
4...Ground fault overvoltage relay, T1, T2...Timer.

Claims (3)

[Claims] [Claim 1] In a loop power transmission system in which loop power transmission circuit breakers are connected to different busbars, a power flow detection relay that detects a power flow flowing to the busbar side via the loop power transmission line; In a loop power transmission system, the loop power transmission system is provided with an overcurrent detection relay that detects overcurrent, and trips a sending-out circuit breaker on the power flow outflow side of the loop power transmission line by the logical product of the operations of the power flow detection relay and the overcurrent detection relay. Overload protection method. [Claim 2] A fail-safe overcurrent detector is provided to detect that the power flow flowing out to the busbar side is an overcurrent state for the loop transmission line, and the loop is detected by logical product with the operation of the fail-safe overcurrent relay. 2. The overload protection system in a loop power transmission system according to claim 1, wherein a sending-out circuit breaker on the outflow side of the power transmission line is tripped. [Claim 3] The loop is operated on the condition that both the undervoltage relay that detects a voltage drop on the bus bar on the side from which power flows out from the loop transmission line and the ground fault overvoltage relay that detects a ground fault in the feeder are in an inoperable state. 2. The overload protection system in a loop power transmission system according to claim 1, wherein a sending-out circuit breaker on the side where the power flow of the power transmission line flows out toward the bus bar is tripped.