The Five Prevention Function of A Switchgear

1- Preventing accidental opening or closing of circuit breakers

The core principle is to ensure that only the designated and correct circuit breaker can be operated.

This is usually achieved through mechanical or electrical coded locks, with only one key corresponding to each breaker, or through a microcomputer-based anti-misoperation interlocking system to prevent incorrect operation of the wrong switch.

2- Preventing the opening or closing of disconnecting switches (or disconnecting plugs) under load

Disconnecting switches lack arc-extinguishing capabilities and must never be operated when there is current in the circuit; otherwise, a huge electric arc will be generated, causing a serious accident.

This is achieved through mechanical interlocking (such as linkage between the operating mechanism and the circuit breaker status) or electrical interlocking. The interlock is only released when the circuit breaker connected in series with it is in the open state, allowing operation of the disconnecting switch.

3- Preventing the connection (or closing) of grounding wires (or grounding switches) while energized

When personnel are working on the equipment or lines, grounding wires must be suspended or grounding switches must be closed to ensure safety. This function prevents accidental closing of the grounding switch or connection of the grounding wire while the equipment is energized, which could cause a three-phase short-circuit grounding accident.

Interlocking Principle: The grounding switch interlock can only be released after the disconnecting switch is open and the line is verified to have no voltage. It is usually interlocked in conjunction with the disconnecting switch.

4- Preventing Closing of the Disconnecting Switch with the Grounding Wire Connected (or the Grounding Switch Closed)

This is the reverse interlocking of the third protection. If the grounding wire is not removed or the grounding switch is in the closed position, closing the disconnecting switch to supply power is prohibited, otherwise a serious short-circuit accident will also occur.

Interlocking Principle: A direct mechanical interlocking device is provided between the grounding switch (or grounding stake) and the disconnecting switch, or an electrical circuit interlock is used.

5- Preventing Accidental Entry into the Energized Compartment

Ensures that personnel cannot accidentally enter the switch cabinet compartment that is operating energized, preventing electric shock.

High-Voltage Detection and Grounding: Entry to the compartment can only be unlocked after following proper voltage detection, discharge, and grounding procedures.

Implementation Methods:
Mechanical Interlock: When the circuit breaker or busbar is energized, the cabinet door is mechanically locked and cannot be opened.

Electromagnetic Lock: When energized, the electromagnetic lock is activated and locks the cabinet door.

Electrified Display Device: Equipped with sensors, this device displays whether the compartment is energized and often works in conjunction with an electromagnetic lock to forcibly lock the cabinet door when energized.

The "five protections" are the material embodiment of power safety regulations and a fundamental line of defense for ensuring the safety of power workers and the stable operation of the power grid.

The design, manufacture, acceptance, and operation of any switchgear must strictly adhere to the "five protections" requirements.