abstract:
This paper introduces the connection mode and characteristics of 500kV 3/2 switch, and connecting with several typical 500kV power outage operation tasks (line power outage and switching operation, bus side switch power outage operation and intermediate switch power outage operation), analyzes the operation sequence of 500kV circuit breaker, points out the correct operation steps, and reduces the probability of misoperation of the circuit breaker.
Key words:
500 kV substation; Knife breaker; operation sequence/order
I. Introduction
500kV substation is responsible for power connection, networking, power transmission, voltage reduction and power supply guarantee in the system. Therefore, the reliability of main wiring power supply in 500kV substation is particularly important. At present, the 500kV main electrical wiring of China Southern Power Grid adopts the highly reliable 3/2 switch wiring mode.
3/2 switch connection means that three switches are connected in series with two buses, and two lines are led out between the two switches (three switches are two lines), each line accounts for 1.5 switches, which is also called one and a half switch connection. The switching operation of 3/2 switch wiring is different from that of double bus and single bus configurations.
From the past operation experience, in the switching operation of power system, the on-load switching accident is one of the malignant misoperation accidents that endanger the safe operation of power grid. It is particularly important to correctly grasp the operation sequence of circuit breakers during operation, so as to avoid or minimize the impact of misoperation accidents on the safe operation of power grid. Article 19 of the Code of Practice for Electric Power Safety stipulates that the power outage operation must be carried out in the order of disconnecting the switch, opening the breaker on the load side and opening the breaker on the bus side. Power transmission operation is the opposite. When the 3/2-connected switch stops sending power, it is sometimes difficult to clearly define the "power side" and "load side" because both sides are power sides, and the bus fault has little effect, so this provision is of little significance. According to the wiring characteristics of 3/2 switch, the line or transformer is more important than the bus. Therefore, it is necessary to analyze the impact of on-load circuit breaker opening and closing accidents on the systems on both sides of the switch to determine the switching sequence.
Second, the line power outage brake operation
In case of power failure of the line, the intermediate switch should be turned off first, and then the bus side switch should be turned off, mainly to prevent the power failure of the line or transformers of the same series (as shown in figure 1). In case of power failure on L3 line, switch 50 12 should be closed first to cut off the small load current, and then switch 50 13 should be closed to cut off all load currents. At this time, if a fault occurs, the bus differential protection of the II bus acts, and the 50 13 and 5023 switches trip to remove the fault, and the main transformer L can continue to run. If the 50 13 switch is turned off first, then the 50 12 switch will be turned off, which will lead to the power failure of the series 1 main transformer.
When a 500kV long transmission line is equipped with a parallel high-voltage reactor, the switch on the reactor side should be disconnected first, and then the switch on the other side should be disconnected. It's just the opposite when sending electricity. In order to avoid the 500kV line with parallel high-voltage reactor without reactor or parallel high-voltage reactor to transmit power, the appropriate stop and transmission terminals should be selected according to the influence of line charging power on the system.
In the wiring of 3/2 switch, when the line power-off switch is closed, the remote tripping device on this side should be stopped and the short lead protection between the two switches should be put into operation.
(a) line or main transformer stop sending operation
Most of the 220kV equipments in 500kV substations are connected by double buses. When the 220kV line stops sending power, the operation sequence of bus-side breaker and line-side breaker is clear, that is, the bus-side breaker is divided into line-side breaker or main transformer-side breaker first, and then into bus-side breaker; During power transmission operation, the circuit breaker on bus side should be closed first, and then the circuit breaker on line side or main transformer side should be closed. This is because the function of circuit breaker is only to make the equipment to be overhauled have enough visual safety distance, establish reliable insulation gap and ensure the safety of maintenance personnel and equipment, so it does not have the ability to cut off load current and short-circuit current. Misclosing during power failure operation, closing the bus side circuit breaker first will lead to failure, which will cause the 220kV bus differential protection to remove the fault point; If the circuit breaker at the side of the line or main transformer is switched off first, the line or main transformer will be protected and the line or main transformer that needs power outage maintenance will be cut off. Compared with the two phases, cutting off a single line or main transformer has less influence on the power grid.
When the 500kV line is powered off, the breaker on the side of the switch line or main transformer is divided first, and then the breaker on the side of the switch bus is divided. The reason is also because when the switch is switched off, the main transformer that cuts off the line or will be blacked out has less influence on the power grid than the bus.
(2) Bus side switch stops power transmission operation.
L, line or main transformer power outage process
If there is an on-load switching accident on the line or main transformer side, the switches on both sides trip, and the fault point is removed to ensure the normal operation of other lines, main transformers and buses; If there is an on-load switching accident on the bus side, all the switches on the bus will trip, resulting in bus voltage loss, reducing the reliability of turtle power supply and threatening the safe operation of the system. Therefore, it should be operated in the order of disconnecting the switch, disconnecting the line or disconnecting the main transformer side circuit breaker and disconnecting the bus side circuit breaker. The power transmission operation sequence is reversed.
2, line or main transformer operation bus power failure (or bus side switch to overhaul operation) such as bus side load switch accident, all switches on the bus trip, remove the fault point, to ensure the normal operation of the line and main transformer; If there is an on-load switching accident on one side of the line or main transformer, the switches on both sides trip, resulting in a power outage accident on the line or main transformer, endangering the safe operation of the power grid. Therefore, it should be operated in the order of disconnecting the switch-opening the bus side circuit breaker-opening the line or the main transformer side circuit breaker. The power transmission operation sequence is reversed.
(3) The intermediate switch stops power transmission operation.
1, 500kV3/2 wiring intermediate switch, one side of the line or main transformer is running, and the other side of the line or main transformer needs power failure. If there is an on-load switching accident on the running side of the line or main transformer, the switches on both sides of the running line or main transformer will trip. If the on-load switch accident occurs on the side that needs power failure, the switches on both sides of the line trip to remove the fault, which will not affect the safe operation of the power grid. Therefore, the operation should be carried out in the order of disconnecting the switch-opening the circuit breaker at the power failure side-opening the circuit breaker at the operation side, and the power failure operation should be carried out in the reverse order.
2, 500kV3/2 line wiring on both sides of the intermediate switch or main transformer is running, the intermediate switch in maintenance power outage operation. The sequence should be considered according to the influence of on-load switch accidents on the power grid on both sides of the switch. That is to say, operate in the order of opening the switch-opening the circuit breaker on the side with less influence on the power grid-opening the circuit breaker on the side with greater influence on the power grid. Power transmission operation should be carried out in the reverse order.
(4) bus stop sending operation
When the line is powered off, the dispatcher will operate the instructions item by item in the prescribed order, and the operators will have no difficulty or objection when executing them. However, when the 500kV bus is cut off, the dispatcher usually only gives comprehensive instructions, and there is no clear instruction to pull the bus-side breaker or the line-side breaker first. The author thinks that the traditional concept that the bus is the power supply side should be abandoned at this time, and the operation order is to pull the bus side breaker first and then the line side breaker. Because the target element of operation at this time is the bus, the purpose of operation is to make the bus power off for maintenance, and the consideration of power grid dispatching operation mode at this time includes bus power off. If there is misoperation at this time, pulling the bus side breaker first will lead to bus cutting, while pulling the line side breaker first will inevitably lead to line tripping. Compared with the two consequences, the impact of 500kV "bus cutting" on the power grid is relatively small.
Three. Concluding remarks
In the switching operation of power system, on-load closing circuit breaker is one of several common malignant misoperation accidents. Through the analysis of the operation sequence of 3/2 switch circuit breaker, the correct operation steps are pointed out, which reduces the accident rate.
References:
[1] Technical Education for Electric Workers of State Power Supply Committee ~.500kV Substation Operation Post Skills Training Textbook [M]. Beijing: China Electric Power Press, 2002.
[2] Jiangsu Electric Power Industry Bureau. Substation operation skill training textbook (500kV substation) M, Beijing: China Electric Power Press, 1999.
[3] Li Lianye, Guo Ke, China Southern Power Grid Corporation Enterprise Standard Q/CSG 10006-2004. Guide to electrical operation. Beijing: China Electric Power Press, April 2004.
;