Switchgear mechanical interlock is a safety interlocking device implemented through a purely mechanical structure. Its core function is to enforce the correct operating sequence, preventing serious accidents caused by human error. It is mainly used in medium and high-voltage switchgear (such as KYN28, XGN, etc.) and is a key measure to ensure the safe operation of the power system.
Main Functions and Purposes
1. Preventing switching of disconnectors under load:
Function: Disconnectors do not have the ability to interrupt load current. Mechanical interlocking ensures that the disconnector can only be operated (opened or closed) when the circuit breaker (load switch) is already open, preventing large electrical arcs caused by switching the disconnector under load, thus preventing equipment damage and personal injury.
2. Preventing accidental entry into live compartments:
Function: Ensures that the cabinet door (especially the cable compartment door or circuit breaker compartment door) can only be opened when the circuit breaker is open and the disconnector is also open, ensuring that both the busbar and line side inside the cabinet are reliably de-energized (or grounded), preventing personnel from accidentally entering live areas and causing electric shock accidents.
3. Preventing energizing when the grounding switch is closed:
Function: When the grounding switch is closed (i.e., in the grounded state, used for maintenance safety), the mechanical interlocking prevents the circuit breaker or disconnector from being closed, preventing energizing a grounded circuit and preventing three-phase short-circuit ground faults.
4. Preventing the closing of grounding switches while energized
Function: The grounding switch can only be closed when the relevant disconnect switch is open and the line is confirmed to be de-energized. This prevents accidental closing of the grounding switch under energized conditions, thus preventing short-circuit accidents.
5. Enforcing the correct operating sequence
Power-on procedure: The grounding switch must be opened first → then the disconnect switch is closed → and finally the circuit breaker is closed.
Power-off and maintenance procedure: The circuit breaker must be opened first → then the disconnect switch is opened → and finally the grounding switch is closed and the door is opened.
Function: Mechanical interlocking forces operators to follow this "five-prevention" logic step by step, fundamentally eliminating incorrect operations due to reversed sequences.
Advantages
High reliability: It does not rely on secondary circuits, power supplies, relays, or PLCs. Its simple physical structure provides strong resistance to interference and extremely high reliability.
Mandatory locking: Once locked, it cannot be operated unless physically damaged, providing a "hard" locking mechanism.
Intuitive and clear: The operation is clear and the locked state is easily understood by maintenance personnel.
Common methods for implementing mechanical interlocks
Locking slot/blocking plate mechanism: A sliding blocking plate obstructs the movement path of the operating shaft or handle.
Program lock/key box: The operating keys of different devices are mutually constrained; the key for the next step can only be retrieved after the previous operation is completed.
Linkage mechanism: Uses shafts, rods, and levers to interconnect and constrain the movement states of multiple operating mechanisms.
Lead screw linkage mechanism: Commonly found in load switch-earthing switch combination devices, where the rotation direction of the lead screw automatically provides interlocking for opening and closing operations.
Summary
The core function of switchgear mechanical interlocks is "error prevention," serving as the physical foundation of the "five safety precautions" required for electrical safety. Through precise mechanical design, it "embeds" safety procedures into the equipment itself, ensuring that both operators and equipment receive the most basic and reliable protection under all circumstances (even if the secondary control system fails). It is an indispensable and crucial line of defense for the safe operation of power systems.
Shaanxi Huadian switchgear incorporates the "five-prevention" safety logic, transforming it into a robust mechanical framework, using physical certainty to eliminate the risk of operational errors. Please contact us for inquiries.
Email:pannie@hdswitchgear.com
Whatsapp/Wechat:+8618789455087
