This article enumerates the application of mechanical key locks in electrical switch operation, and avoids the occurrence of misoperation accidents from technical measures.
The mechanical plug-in key interlock for electrical equipment is a safety operating system, which must be operated in a prescribed order to prevent human error, otherwise subsequent operations cannot be performed to ensure the safety of personal equipment. The interlock method is simple , reliable, direct and effective, especially suitable for interlocking between multiple cabinets or doors. Operators can easily identify and eliminate misuse. Widely used in power plants, metallurgy and other fields.
This paper takes the power supply outage during the maintenance of the dry-type transformer, frequency conversion cabinet and electrostatic precipitator of the power plant as an example, and explains how the mechanical key realizes the interlocking operation from the technical measures.
According to the requirements of the power operation specification, the dry-type transformer maintenance should first disconnect the low-voltage 380V switch, then disconnect the high-voltage 6kV switch, then ground the 6kV switch, and finally open the transformer door for maintenance. transformer. According to this operation sequence, install mechanical locks on the 380V switchgear, 6kV switchgear grounding knife and transformer door respectively.
When in operation, a key can only be removed by disconnecting the 380V circuit breaker. At this point, the 380V circuit breaker is locked in the off state. Take this key to open the grounding knife in the 6kV switchgear (note: the self-locking of the 6kV circuit breaker and the grounding knife can be used here). The ground knife is grounded and the other key is pulled out. The grounding knife is locked in the grounded state.
At this time, ensure that the low-voltage and high-voltage switches are powered off and grounded. Finally take out the key to open the transformer door for transformer maintenance. The high and low voltage switches can be powered by reverse operation (as shown in Figure 1).
figure 1
Interlock operation sequence: turn off the 380V switch, pull out the key 2a, the cabinet is locked in the power-off state → turn off the 6kV switch, unlock the 6kV side grounding knife with the key 2a, ground the grounding knife, pull out the key 2B, the grounding knife is locked in the grounding Status → use key 2B to open the dry-type transformer high-voltage side cabinet door, pull out key 2C → use the key to open the dry-type transformer low-voltage side cabinet door 2C. After the power is turned on, the staff can repair the transformer.
According to the requirements of the electrical switch operation specification, the power-on operation of the inverter cabinet (as shown in Figure 2) is to confirm that the bypass switch K3 is disconnected before closing the outgoing switch K2, then close the incoming switch K1, and finally supply power to the upper-level high-voltage switch. The power-off operation of the inverter cabinet is to first disconnect the upper high-voltage switch, then disconnect the knife switch of the incoming cabinet, and then disconnect the outgoing knife switch.
The power-on operation of the inverter cabinet is to confirm that the incoming switch and outgoing switch are disconnected, the bypass switch is closed, and the upper high-voltage switch is closed. The power frequency power-off operation of the inverter cabinet is to first disconnect the upper high-voltage switch, and then disconnect the bypass switch.
According to the above operation requirements, install a mechanical lock on the high-voltage switchgear, and then install two mechanical locks on the incoming switch, outgoing switch and bypass switch respectively. One lock implements the switch open and the other lock implements the switch closed. When the inverter cabinet is powered off, first disconnect the high-voltage switch, pull out the lock key of the high-voltage switch, and the high-voltage switch is locked in the power-off state.
figure 2
Use this key to unlock the incoming line switch, disconnect the incoming line switch, lock the switch, pull out the key, the incoming line switch is locked in the off state. Unlock the socket switch with the extracted key, disconnect the socket switch, remove the key, the socket switch is locked in the off state.
Use this key to unlock and power on the bypass cabinet knife switch, and then pull out another key on the bypass knife switch to supply power to the high-voltage switch, so as to realize the conversion of the fan from the frequency conversion mode to the power frequency mode.
The primary fan B1 is normally in the frequency conversion working state: the K1 and K2 knife switches are closed, and the K3 knife switch is open. Frequency power inverter bypass interlock operation sequence: