Mechanical interlocking requirements for American standard medium voltage switchgear

The standard for American medium voltage switchgear is C37.20.2, with metal armor, air insulation, double-layer circuit breaker switchgear design. Generally, the width of the 15/27kV switchgear is 36 inches 914mm, the depth is 90 inches 2286mm, and the height is 95 inches 2413mm.

The safety measures of American standard switchgear are very important and must be equipped with sufficient mechanical interlocks, key locks, padlocks, and other devices to ensure safety.

Metal enclosed structure or insulation material enclosed mechanism; The circuit breaker should be a withdrawable structure or have equivalent measures that can safely disconnect the circuit breaker when the busbar is energized.  

Sufficient grounding and short-circuit equipment should be provided to ensure safe maintenance of the circuit; The cable entrance should have measures to prevent water leakage along the inside of the cable switchgear; Instruments, switches, indicator lights, buttons, operating handles, etc. should have durable nameplates indicating their purpose and operating position. All charged bodies are enclosed in grounded metal compartments, automatic valves, main circuit bus conductors, and connections are all insulated, and circuit breaker compartment doors can be used as relay mounting plates.

The handcart drive auxiliary contact TOC is a fixed auxiliary switch installed inside the compartment to provide position signals for the circuit breaker when it is in the working position. TOC/NO - When the circuit breaker is not in the working position, the auxiliary switch is in the normally open position, and TOC/NC - When the circuit breaker is in the working position, the auxiliary switch is in the closed position.

Mechanism driven auxiliary contact MOC, a fixed auxiliary switch installed inside the compartment, is used to provide position signals for the circuit breaker in the open and closed positions. MOC/NO - when the circuit breaker is in the open position, the auxiliary switch is in the normally open position, MOC/NC - when the circuit breaker is in the closed position, the auxiliary switch is in the closed position.

Continuous interlocking should be provided to ensure the correct operation sequence: a. The circuit breaker cannot be pulled out from the connection position in the closed state; b. The circuit breaker cannot be closed without complete engagement or sufficient safety distance from the charged body; c. Corresponding means should be provided to securely hold detachable components in the housing when they are in a connected or tested state; When the compartment door is closed, an independent isolation position is required to ensure that the detachable components can be firmly held in that position. d. Only when the secondary circuit is disconnected can the voltage transformer fuse be approached or isolated; e) Circuit breakers equipped with energy storage mechanisms should be designed to not release stored energy until the energy storage mechanism has fully stored it;

f) Operators and service personnel should prevent the impact of accidental release of stored energy through any of the following methods: 1) Install interlocking devices inside the enclosure to prevent the circuit breaker from completely withdrawing from the enclosure when the energy storage mechanism is storing energy. 2) Provide appropriate devices to prevent the circuit breaker from fully exiting until the closing function is blocked. 3) There is a mechanism that can automatically release stored energy before or during the process of pulling the circuit breaker out of the housing. If the stored energy is released before the circuit breaker is removed from the connection position, auxiliary electrical interlocking devices must be equipped to prevent the re storage of stored energy.

g) A locking device should be provided to prevent the circuit breaker from moving to the connection position.

Pull out circuit breakers should have mechanical locking mechanisms in both the working and disconnecting positions. When the circuit breaker is in the pulled out state, the live static contacts are automatically covered;

The following measures can be taken to prevent accidental contact of the spring energy storage mechanism by operators: 1. When the circuit breaker mechanism is storing energy, the interlock should prevent the circuit breaker from being safely withdrawn from the compartment; 2. When the circuit breaker is closed, the interlock should prevent the circuit breaker from being pulled out of the compartment; 3. When the circuit breaker is pulled out, the operating mechanism automatically releases energy, and electrical interlocking should be provided to ensure that the circuit breaker will not automatically store energy again; The energy storage state of the circuit breaker cannot be shaken into the working position.

Install a padlock on the padlock valve mechanism to prevent it from opening; Shake in the hole baffle padlock to prevent opening; Install a padlock on the high-voltage compartment door to prevent it from opening;

The circuit breaker prevents the closing padlock, and there are two positions on the rocking mechanism, each of which may be equipped with three padlocks. The previous position can prevent the circuit breaker from closing when in the "test" and "connection" positions. Push the slider backwards and insert the padlock into the slot opening located in front of the key lock. This has the same interlocking function as a key lock and will not hinder the movement of the rocking mechanism.

It is forbidden to shake out the padlock when closing the circuit breaker. The second position of the lock is behind the key lock. The lock in this slot will prevent any movement of the rocking mechanism by blocking the hexagonal rotation axis.

There is a device for key locking on the left side circuit breaker rocker arm mechanism track of the key lock. The function of this lock is to prevent the circuit breaker from closing in the "test" and "connection" positions by operating the interlocking device. To remove the key, push the slider backwards and insert the lock bolt into the slot. This allows the key to be removed while preventing the circuit breaker from closing. The key lock does not hinder the movement of the rocker arm mechanism.