Ensuring the safety of the operating mechanism: Frequent closing and opening operations can severely impact the circuit breaker's operating mechanism, causing mechanical wear or damage.
III. Types of Anti-trip Circuits
Anti-trip circuits are primarily divided into two categories: electrical and mechanical. Modern vacuum circuit breakers (especially those in the medium and high voltage range) typically utilize electrical anti-tripping, or a combination of electrical and mechanical solutions.
Electrical Anti-tripping
Electrical anti-tripping is implemented using relays and contact logic and is the most common and reliable method. There are two main wiring methods:
a) Series Anti-tripping (Current Start, Voltage Hold)
This is currently the most mainstream and widely used anti-tripping solution.
Core Components:
Anti-tripping Relay (TBJ): A dual-coil relay with a current start coil and a voltage hold coil, or a single-coil relay with latching contacts.
TBJ's Normally Open Contact (TBJ-1): Connects the voltage coil latching circuit.
TBJ's Normally Closed Contact (TBJ-2): Connected in series with the closing circuit, it interrupts the closing command.
Operating Principle:
Closing: When a closing command is issued, closing current flows, one path closing the circuit breaker and the other flowing through the current coil of the anti-tripping relay TBJ, causing it to trip.
Starting and Holding: After TBJ trips, its Normally Open Contact TBJ-1 momentarily closes, connecting the TBJ voltage coil circuit and holding it.
Closing: Simultaneously, its Normally Closed Contact TBJ-2 momentarily opens. At this point, even if the closing command persists, the closing circuit has been disconnected by TBJ-2, preventing further closing.
Reset: When the closing command finally disappears, the TBJ voltage coil loses power, the relay resets, and the normally closed contact TBJ-2 recloses, restoring the closing circuit and preparing for the next normal closing attempt.
Advantages:
High reliability and reliable anti-tripping effect.
Effectively prevents tripping caused by sticking closing contacts.
This is a standard design and recommended solution in the relay protection industry.
Disadvantages:
Wiring is slightly more complex, requiring a dual-coil relay or an additional self-holding circuit.
b) Parallel anti-tripping (voltage-start, voltage-holding)
This method is more traditional and is now rarely used in new projects.
Core Components:
Anti-tripping relay (TBJ): A standard voltage-type relay
TBJ's normally closed contacts: Connected in series in the closing circuit.
The circuit breaker's normally open auxiliary contacts.
Operating Principle:
Closing: Issue a closing command, and the circuit breaker closes. Starting: After the circuit breaker is closed, its normally open auxiliary contacts close. At this point, if the closing command persists, voltage is applied to the TBJ coil through the closing circuit, causing it to actuate.
Severing Closing: After the TBJ actuates, its normally closed contacts, connected in series with the closing circuit, open, disconnecting the closing circuit and preventing further closing.
Resetting: After the closing command disappears, the TBJ resets upon power failure.
Disadvantages: If the circuit breaker's auxiliary contacts are improperly adjusted or unresponsive, anti-tripping may fail.
It cannot effectively handle the situation where the closing contacts stick momentarily.
It is less reliable than a series-type circuit breaker.
Mechanical Anti-tripping
The mechanical anti-tripping function relies on the structural design of the circuit breaker's operating mechanism.
Operating Principle: Take a spring operating mechanism as an example. When the mechanism is in the closed position, the closing spring is fully charged. If a closing command is received at this point, since the mechanism is already in the closed position, an internal mechanical locking mechanism prevents further closing, thus preventing tripping. The closing command becomes effective only after the circuit breaker is opened and the spring recharges.
Advantages:
Simple structure, requiring no additional electrical wiring or relays.
Reduced cost.
Disadvantages:
It does not prevent the closing coil from being burned out by a prolonged closing command. Even if the mechanism does not operate, a prolonged closing signal can cause the closing coil to be energized and burn out.
The reliability of the anti-tripping mechanism depends entirely on the machining accuracy and wear of the mechanical components.
Electrical standards generally do not consider purely mechanical anti-tripping a reliable anti-tripping measure.
Conclusion
For vacuum circuit breakers, the most reliable and recommended anti-tripping solution is a "series (current-starting, voltage-holding) electrical anti-tripping circuit." This is considered a mandatory standard during design, construction, and operation and maintenance.
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