What are the common faults of high voltage circuit breakers?

High-voltage circuit breakers are critical protection and control devices in power systems, and their reliability is crucial. Common faults can be divided into several categories, which are detailed below:

1. Operating Mechanism Failure 

The operating mechanism is the "muscle" of the circuit breaker, responsible for completing the opening and closing operations and the most prone to failure.

Mechanical Jam/Refusal to Operate:

Refusal to Open: The circuit breaker refuses to open after receiving the opening command. This is one of the most dangerous faults and can prevent the fault from being cleared, potentially escalating the accident.

Refusal to Close: The circuit breaker refuses to close after receiving the closing command.

Causes: Mechanical components such as the connecting rod or pin become stuck due to wear, deformation, rust, or lack of lubrication; poor buffer performance; improper installation and adjustment; etc.

Pressure Relief/Abnormal Pressure:

Mainly affecting hydraulic/pneumatic mechanisms:

Hydraulic mechanisms: Frequent oil pump activation, abnormal pressure increases or decreases, internal or external oil leakage in the hydraulic system. Causes include aging and damage of seals, valve body wear, and microswitch malfunction.

Spring Mechanism: Closing or opening springs fail to store energy, or the springs become fatigued or broken.

Pneumatic mechanism: low or too high compressed air pressure, air line leakage, air compressor failure.

Burned-out opening/closing coil:

The coil is the power source of the electromagnetic mechanism. If the circuit breaker's auxiliary contacts fail to switch properly or if there is poor contact, the coil will remain energized for an extended period of time, leading to overheating and burnout, resulting in a malfunction.

 

2. Arc Extinguishing Chamber and Insulation Failure

The arc extinguishing chamber is the "heart" of the circuit breaker, responsible for extinguishing the arc. Failure can have serious consequences.

Degraded or ineffective arc extinguishing capability:

Interrupting failure: When interrupting the short-circuit current, the arc cannot be extinguished, potentially causing the arc extinguishing chamber to burn out, explode, or even cause a system failure.

Causes: Deterioration of the arc extinguishing medium (such as SF6 gas or vacuum); burnout of the nozzle (in the SF6 circuit breaker); severe electrical wear and excessive erosion of the contacts.

Insulation Deterioration:

Internal Flashover/Breakdown: Dielectric strength decreases within the arc extinguishing chamber, between the conductor and ground, or between the interrupted contacts, leading to breakdown under overvoltage or normal operating voltage.

Causes:

SF6 circuit breakers: Insufficient SF6 gas purity, excessive water content, or gas pressure below the latching value.

Vacuum circuit breakers: Loss of vacuum within the vacuum bulb ("de-vacuum"), manifested as a pale blue glow within the chamber and a sharp deterioration of insulation performance.

Oil-fired circuit breakers: The insulating oil ages, becomes damp, and carbonizes, reducing insulation strength.

The insulating rods become damp, age, and crack.

 

3. Conductive Circuit Failure

Increased Contact Resistance:

Symptom: The circuit breaker body heats up, which in severe cases may cause thermal runaway, burning the contacts and supporting porcelain.

Cause:

Primary conductive circuit: Poor contact between the static and moving contacts (such as burnout, oxidation, or silver plating loss); poor contact between the intermediate contacts; loose terminal block bolts.

Secondary conductive circuit: Loose current transformer terminals.

Contact Wear:

Each time the circuit breaker is opened and closed, especially when opening or closing short-circuit currents, the contacts are subject to arc erosion. Over time, the contact material wears and becomes thinner, affecting contact performance and breaking capacity.

 

4. Secondary Component and Control Circuit Failures

This is the circuit breaker's "nervous system." Failure can cause control failure or malfunction.

Auxiliary Switch Failure:

The auxiliary switch is mechanically linked to the main contacts and is used to switch the control circuit. Poor contact or incomplete switching is a common cause of coil burnout or circuit breaker failure.

Microswitch/Pressure Switch Failure:

This is used to monitor mechanism pressure, spring charge status, and other factors. Switch failure can cause the latching function to fail or erroneous signals to be issued.

Control Circuit Wire Break/Grounding:

Loose terminals, damaged cable insulation, and other issues can cause the control circuit to become blocked or short-circuited, rendering the circuit breaker inoperable.

 

5. External and Sealing Failures

Seal Failure:

SF6 gas leakage: This is one of the most typical SF6 circuit breaker failures. Causes include aging of the seal ring and poor sealing between the porcelain sleeve and the flange, which can lead to leakage and reduced insulation and arc extinguishing capabilities.

Hydraulic mechanism oil leakage: This can cause pressure drop and circuit breaker lockout.

Ceramic bottle failure:

Support porcelain bottles/casing porcelain bottles: These can crack or explode due to pollution flashover (flashover under dirty conditions), ice flashover, excessive mechanical stress (such as vibration during operation), or manufacturing defects.

 

Summary and Prevention

High-voltage circuit breaker failures are often the result of a combination of factors. To ensure reliable operation, the following measures must be taken:

Strengthen regular inspection and maintenance: Lubricate, inspect, and adjust the operating mechanism in strict accordance with regulations.

Perform preventive testing, such as measuring loop resistance, dielectric loss factor, SF6 gas moisture content, vacuum level, and mechanical property testing, to promptly identify potential defects.

Utilize online monitoring technologies, such as monitoring SF6 gas density, tripping and closing coil current waveforms, vibration signals, partial discharge, and contact electrical life, to perform condition-based maintenance.

Improve installation and maintenance quality: Ensure all mechanical dimensions and electrical connections are correct and reliable.

The above analysis shows that high-voltage circuit breaker failures primarily occur in two core components: the operating mechanism and the arc extinguishing chamber/insulation system. These are areas that require key attention during routine operation and maintenance.

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