What are the functions of the anti-tripping and interlocking mechanisms in high-voltage vacuum circuit breakers?

The "anti-tripping" and "interlocking" functions of high-voltage vacuum circuit breakers are two crucial protection and control features. They serve completely different purposes, but both are essential for the safety of the equipment and system.

I. Anti-pumping

1. Core Function:
To prevent the circuit breaker from repeatedly cycling through "closing-tripping-reclosing-retripping" while the closing signal remains active due to the continuous presence of fault current. This phenomenon is called "pumping."

 

2. Scenarios that cause "pumping":
Assume the circuit breaker is in the open position, and an operator or automatic device issues a continuous closing command.

Step 1: The circuit breaker executes the closing operation.

Step 2: At the moment of closing, if a permanent fault exists on the line (e.g., a ground wire is not removed), the relay protection device will immediately detect the fault current and quickly issue a tripping command, causing the circuit breaker to open.

Step 3: At this point, if the closing command is still present (e.g., the operator is still holding down the closing button, or the contacts of the automatic closing device are stuck), the circuit breaker will immediately perform another closing operation after the closing circuit is re-energized.

Step 4: The fault still exists after closing, and the protection device trips again...

This process will repeat several times at a very high speed, causing the circuit breaker to close into the fault current multiple times within a few seconds.

 

3. The dangers of "jumping":

Damaged or exploding circuit breakers: Repeated closing onto short-circuit currents generates enormous electrodynamic forces and arc heat effects, severely damaging core components such as the vacuum interrupter and contacts, and can even lead to the circuit breaker exploding.

Expanded scope of the accident: Continuous short-circuit current surges can damage other equipment on the line (such as transformers and current transformers).

Threat to system stability: Causes continuous and severe shocks to the power grid.

 

4. Principle of Anti-Reclosing Function:
The anti-reclosing function is usually implemented through an intermediate relay called an "anti-reclosing relay." It has a current-activated coil and a voltage-holding coil.

When a protective device trips, the tripping current activates the anti-reclosing relay.

After the relay operates, it uses its normally closed contact to disconnect the closing circuit and simultaneously uses its normally open contact for self-holding.

In this way, as long as the closing command does not disappear, the anti-reclosing relay will remain energized, thus firmly "locking" the closing circuit and preventing it from being reconnected.

Only when the closing command is completely released will the anti-reclosing relay reset, and the closing circuit will return to normal.

Summary: The core of the anti-reclosing function is to "protect the circuit breaker itself," preventing it from suffering destructive repeated closing impacts due to control circuit faults or human error.

 

II. Interlock/Lockout

1. Core Function:
To forcibly prevent the circuit breaker or its related equipment from performing closing or opening operations when it is in an abnormal or unsafe state, thereby ensuring personal and equipment safety. The logic of interlocking is more complex than that of anti-tripping, involving more conditions.

 

2. Common Interlock Conditions and Functions:

a. Electrical Interlocks:

Spring Operating Mechanism Not Fully Charged Interlock: If the spring is not fully charged, the circuit breaker will not have enough energy to complete the closing operation. Forcing the closing operation at this time will lead to failure or even damage to the mechanism. Therefore, the closing circuit will be locked.

Low Gas Pressure Interlock: For some circuit breakers (or combined switchgear) that use SF6 gas as the insulating medium, when the gas pressure is below the safe value, the insulation and arc extinguishing capabilities will decrease. At this time, both the closing and opening circuits will be locked to prevent accidents caused by operating the circuit breaker under insufficient insulation.

Control Power Loss Interlock: After losing the control power, the circuit breaker cannot be operated electrically.

 

b. Mechanical and Logic Interlocks:

Grounding Switch Position Interlock: This is one of the most important safety interlocks. When the grounding switch is in the closed position (line grounded), the circuit breaker is absolutely prohibited from closing. This is to prevent serious accidents caused by energizing a grounded line, directly protecting the life safety of operating personnel.

Circuit Breaker Trolley Position Interlock (for withdrawable switchgear): The circuit breaker trolley can only perform opening and closing tests in the "test position," and can only connect to the main circuit in the "working position." When the trolley is in an intermediate position, it will be locked and unable to close.

Disconnector Switch Position Interlock: In some main wiring schemes, a strict operating sequence is required between the disconnector switch and the circuit breaker (such as closing the disconnector switch first, then the circuit breaker). Interlock logic is used to prevent misoperation.

 

3. Methods of implementing interlocking:

Mechanical interlocking: Directly prevents the movement of operating components through mechanical structures (such as baffles, connecting rods, keys, etc.).

Electrical interlocking: Uses the contacts of auxiliary switches (such as the normally closed contact of a grounding switch, or a limit switch indicating the position of the switchgear) connected in series in the closing control circuit of the circuit breaker. When the conditions are not met, the contacts open, and the closing circuit is interrupted.

Summary: The core of interlocking is to "ensure the operating procedure and safety conditions," and it is a preventative safety measure that ensures the circuit breaker can only be operated when all safety conditions are met.

 

Summary and comparison

Characteristics	Anti-pumping	Interlock
Main Purpose	Prevents the circuit breaker from repeatedly opening and closing due to a fault.	Prevents operation of the circuit breaker under unsafe conditions.
Protected Objects	Mainly concerns the circuit breaker itself.	Applies to operators, circuit breakers, and related power grid equipment.
Trigger Conditions	Occurs when a trip signal and a continuous closing signal are present simultaneously.	Multiple safety conditions must be met (e.g., sufficient stored energy, no grounding, sufficient gas pressure, etc.).
Action Results	Only blocks the closing circuit, allowing the opening circuit to operate.	May interlock closing, opening, or both.
Nature	A specific, automatic control and protection logic.	Governed by a wide range of safety rules and conditions.

In simple terms:

Anti-tripping prevents the circuit breaker from closing when it shouldn't.

Interlocking prevents operation altogether when the conditions are not met.

Both are indispensable safety features in the design of high-voltage vacuum circuit breakers and their switchgear.

 

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