What are the causes of failures in low-voltage switchgear circuit breakers themselves?

Based on years of field statistics on switchgear accidents, combined with analysis focusing on the circuit breaker itself, the main causes have been identified as: failure of operation mechanism; insulation faults; poor breaking and closing performance; and poor conductivity.

1.Failure of Operation Mechanism

Failure of operation mechanism manifests as delayed operation or unintended operation. Since the most basic and important function of a high-voltage circuit breaker is to operate correctly and rapidly isolate power system faults, delayed or unintended operation poses a serious threat to the power grid, primarily in the following ways:

• Expanding the scope of the fault—what was originally a single-circuit fault may escalate to affect the entire busbar, or even cause a complete substation or plant blackout;

• Prolonging fault clearance time, which affects system stability and exacerbates damage to controlled equipment;

• Causing unbalanced (non-full-phase) operation, which often leads to abnormal operation of protective relays and system oscillations, easily escalating into a system-wide or large-scale blackout.

The main causes of operation mechanism failure include:

• Defects in the operating mechanism;

• Mechanical defects in the circuit breaker itself;

• Defects in the operation (control) system.

2.Insulation Accidents

Circuit breaker insulation accidents can be divided into internal insulation accidents and external insulation accidents. Internal insulation accidents generally cause more severe consequences than external ones.

2.1 Internal Insulation Accidents

Mainly involve bushings and current-related incidents. The primary cause is moisture ingress due to water penetration; secondary causes include oil deterioration and insufficient oil level.

2.2 External Insulation Accidents

Primarily caused by pollution flashover and lightning strikes, leading to flashover or explosion of the circuit breaker. The main reason for pollution flashover is that the creepage distance of porcelain insulators is too short for use in polluted areas; secondly, oil leakage from the circuit breaker allows dirt to accumulate easily on the porcelain skirts, triggering flashover.

3. Breaking and Closing Performance Failures

Breaking and closing operations represent the most severe test for a circuit breaker. The vast majority of breaking and closing failures are primarily due to obvious mechanical defects in the circuit breaker; secondarily due to insufficient oil or oil not meeting required specifications. Some cases are also attributed to inadequate interrupting capacity of the circuit breaker. However, the former is more common, as a considerable number of failures occur even during switching of small loads or normal load currents.

4. Poor Conductivity Failures

Analysis of field accident statistics shows that poor conductivity failures are mainly caused by mechanical defects, including:

• Poor contact—such as unclean contact surfaces, insufficient contact area, or inadequate contact pressure;

• Detachment or jamming—for example, detachment of copper-tungsten contacts;

• Loose screws at contact points;

• Broken flexible connectors.