Analysis of Common Problems in Electrical Switching Operation

Whether it is the start stop of the unit, the normal operation of the unit, or in case of accidents, electrical switching operation is an important part of daily work. Due to the implementation of duty officers for domestically produced 200MW units and the optimization of personnel combinations, the number of electrical duty officers has decreased, and there are not many experienced personnel. In terms of electrical engineering, the technical level and quality of personnel cannot keep up with the current situation, and there is a shortage of manpower in the electrical field. Although on duty personnel are implemented, there are limitations in learning and there is still a significant gap in the execution of switching operations. Especially for non electrical personnel, the operation of electrical switching is not standardized, and most people have no knowledge of electrical switching operation. Therefore, discuss the electrical switching operation.

1. Interpretation and Principles of Electrical Switching Operation

There are three states of electrical equipment, namely operation, standby (cold standby, hot standby, linked standby), and maintenance state; The operation of switching electrical equipment from one state to another is called switching operation.

The principle of switching operation:

Central principle: Do not pull or close the knife switch with load

1.1 When opening and closing the circuit breaker, use a switch to connect and disconnect the load current and short-circuit current. It is prohibited to use a knife switch to cut off the load current;

1.2 When closing, it should be done from the power side first. After checking that the switch is in the off position, the busbar side knife switch should be closed first, then the load side knife switch should be closed, and finally the switch should be closed. Because during power transmission when the circuit is closed, it is possible that the switch may not be detected in the closed position; If the line side knife switch is closed first and then the bus side knife switch is closed, a strong arc will be generated between the knife switch contacts when the knife switch is closed with load, which will damage the equipment and even cause a bus short circuit, thereby affecting the operation of other equipment. If the busbar side knife switch is closed first, and then the line measuring knife switch is closed, although the knife switch is closed with the same load, due to the relay protection action of the busbar switch, it automatically trips, isolates the fault point, and does not affect the operation of other equipment; At the same time, the maintenance of the line side knife switch is relatively simple, and only one line needs to be stopped. When repairing the busbar side knife switch, the busbar is stopped, which has a large impact.

1.3 When pulling the switch, it should be done from the load side first. After opening the switch and checking that it is in the disconnected position, the load side knife switch should be opened and the power supply knife switch should be opened. For transformers with switches on both sides, during a power outage, the load side switch should be disconnected first to cut off the load current, and then the power side switch should be disconnected to only cut off the transformer's no-load current. Because if the switch is not detected in the closed position, it will cause the load to pull the knife switch, resulting in a fault on the line. Due to the action of the line relay protection, the switch will automatically trip, isolate the fault point, and not affect the operation of other equipment. If the power side knife switch is opened first and then the load side knife switch is opened, although it is also a loaded knife switch, the fault will occur on the busbar, expanding the fault range and affecting the operation of other equipment.

1.4 When reversing the busbar, the opening and closing steps of the knife switch are to first close the knife switches that need to be switched to one group of busbars one by one, and then open the knife switches running on the other busbar one by one. This can avoid misoperation accidents caused by closing and pulling one knife switch; But sometimes it also depends on specific circumstances.

1.5 The following equipment is allowed to be pulled and closed with a knife switch:

1.5.1 Pull and close the fault free lightning arrester and voltage transformer on the busbar;

When the bus tie switch is closed, switch the operating mode of the system;

1.5.3 Under normal circumstances, switch the neutral point operation mode of the main transformer;

1.5.4 Use a knife switch with an arc extinguishing cover. When there is a partition between the knife switch and the operating handle, it is allowed to cut load currents below 30 amperes (380V system);

When all load switches on the busbar are disconnected, charge and cut off power to the busbar without any faults.

1.6 It is prohibited to use a knife switch for the following operations:

1.6.1 Load pulling switch;

1.6.2 Use a knife switch to stop power transmission to the line;

1.6.3 Input and disconnect the main transformer and all auxiliary transformers;

1.6.4 Cut off the grounding current at the fault point.

2. Basic requirements for electrical switching operation

2.1 Basic requirements for operating the knife switch:

2.1.1 When manually closing the knife switch, be quick and decisive, but do not apply too much force at the end of closing to prevent over closing and damage to the supporting porcelain bottle. Attention: If arc light occurs at the beginning of closing, the knife switch should be quickly closed.

When manually pulling the knife switch, it should be done slowly and cautiously, especially when the moving contact of the knife switch has just left the stationary contact. If an arc occurs, it should be immediately closed and the operation stopped. However, when cutting small capacity transformers, the charging current of overhead lines and cables of a certain length, a small amount of load current, and the use of knife switches to disconnect the ring, arcs are generated. At this time, the knife switch should be quickly pulled open to extinguish the arc at zero crossing.

2.1.3 After accidentally closing the knife switch, it is strictly prohibited to close or open the knife switch. The circuit switch should be disconnected and it should be confirmed that there is no current passing through the knife switch before the accidentally closed knife switch can be closed or opened.

2.1.4 Before closing the knife switch, check that the switch is in the "OFF" position.

2.1.5 When the knife switch cannot be operated, the reason should be carefully investigated and forced operation should not be carried out to prevent damage to the knife switch.

2.1.6 The power supply and power-off operation of the knife switch should be carried out with the corresponding switch (contactor) disconnected; After the knife switch operation is completed, check that the dynamic and static contacts are in good contact, verify that the knife switch position is correct, and then lock the distribution cabinet door.

Before operating the knife switch, if any abnormalities or defects are found, the operation should be stopped, measures should be taken or the defects should be eliminated before resuming the operation. Do not act recklessly.

When the knife switch cannot be opened or closed, it is strictly prohibited to forcefully pull or close it. The reasons should be carefully investigated, such as whether the operating mechanism is intact, whether there is a grounded knife switch in the circuit, whether the switch is in the open position, etc. If it cannot be handled, notify the maintenance team for assistance. The knife switch gets stuck during operation and cannot be forcefully operated. You can manually operate the handle of the knife switch a few times and then close it again; If there is still jamming and no contact discharge occurs, immediately stop the operation. If discharge has occurred and cannot be extinguished, the knife switch should be disconnected from the live system.

2.2 Basic requirements for switch operation

2.2.1 In general, switches are not allowed to be manually closed.

2.2.2 Do not use remote control switch