High voltage circuit breaker can not be closed

The high-voltage circuit breaker is a critical component in any power system. Recently, I had the opportunity to analyze some issues related to high-voltage circuit breakers that failed to close properly, and I'd like to share my findings and solutions for these problems. Understanding these issues can significantly reduce downtime and minimize losses for users.

Case 1: High Voltage Circuit Breaker Fails to Close

Faulty Equipment: A 10kV high voltage switchgear.

Symptoms: This high voltage cabinet controls a 10kV overhead line. After completing the line maintenance, we were ready to turn it back on. However, when the microcomputer sent a closing command, the circuit breaker exhibited a continuous "close-trip" behavior, leading to delays in power restoration for several hours and causing financial losses for the client.

Diagnostic Analysis:

1. Checked the DC operating power supply—found it to be functioning correctly.

2. Inspected the closing contactor, intermediate relay, and wiring—all showed no abnormalities. Additionally, the closing contactor was triggered.

3. Examined the circuit breaker's operating mechanism and discovered that the bracket and roller shaft were improperly aligned, preventing the closing mechanism from holding its position.

Solution: Adjusting the closing mechanism resolved the issue.

[Summary of Experience]: Common causes for a circuit breaker tripping upon closing include low battery voltage, damaged silicon rectifier components, early disconnection of auxiliary normally closed contacts, sticky relay contacts, and improper adjustments in the operating mechanism.

Case 2: High Voltage Circuit Breaker Fails to Close

Faulty Equipment: A 10kV high voltage switchgear.

Symptoms: During the closing operation, the circuit breaker could not be electrically closed.

Diagnostic Analysis:

1. Manual operation worked fine, indicating no mechanical transmission issues.

2. The closing control circuit, relays, closing coils, auxiliary contacts, and wiring were all intact.

3. Besides the operating mechanism and electrical circuit problems, one must consider the operating power supply. This circuit breaker uses a DC battery pack that has been operational for several years. A few months ago, it was noted that the battery voltage had dropped significantly.

4. Measuring the closing bus voltage gave 215V, which seemed sufficient. However, this is the no-load voltage. During closing, the inrush current can reach 100A or more. If the battery pack is faulty, the internal resistance increases, causing a noticeable drop in terminal voltage.

5. Actual measurements revealed that during closing, the terminal voltage of the battery pack fell below 100V. While the closing iron core moved, the electromagnetic force wasn't strong enough to lift the mechanism, thus preventing the circuit breaker from closing.

Solution: Replaced the defective battery pack.

[Summary of Experience]: In substations using a DC operating power supply, it’s essential to use maintenance-free battery packs. Regular checks are necessary to identify and replace any non-compliant batteries promptly to ensure the operating system functions correctly.

Case 3: High Voltage Circuit Breaker Fails to Close

Faulty Equipment: 5# high voltage switchgear (10kV, controlling a 1600kVA power transformer) in a company substation.

Symptoms: During the closing process of the circuit breaker, a loud "嘣" sound emanated from the switch cabinet, and the closing operation failed.

Diagnostic Analysis:

1. The circuit breaker is a ZN28-10 drawer-type vacuum circuit breaker. Upon pulling out the drawer for inspection, the actual mechanical position of the circuit breaker was shown as open, but the electrical display indicated that the C-phase circuit remained charged.

2. The external appearance of the vacuum interrupter was examined. Through the glass casing, it was observed that the A-phase and B-phase vacuum arc-extinguishing chambers appeared normal, with clean and shiny shields. However, the inner shield of the C-phase arc-extinguishing chamber was blackened, showing clear burn marks and significant degradation.

3. An AC voltage withstand test on the three phases revealed that both the A-phase and B-phase met the specifications (42 kV/min). When testing the C-phase, the vacuum interrupter broke down at just 3 kV.

4. According to power industry standards, the gas pressure inside the vacuum interrupter should not exceed 6.6×10²Pa at the end of its allowable storage period, and when shipped, it shouldn’t exceed 1.33×10²Pa. Using a vacuum tester, the vacuum levels were found to be 4×10²Pa for Phase A, 3.4×10²Pa for Phase B, and 5×10²Pa for Phase C. This shows that the vacuum integrity of the C-phase arc-extinguishing chamber had essentially failed.

Solution: Replaced the C-phase vacuum circuit breaker.

[Summary of Experience]: Vacuum circuit breakers, which use vacuum as their medium and arc-quenching mechanism, are crucial control and protection devices in power systems. Any faults or defects can impair their ability to control and protect, potentially leading to grid failures and accidents. Therefore, regular inspections of the vacuum degree and insulation performance of vacuum circuit breakers are vital, and any units nearing their service life or exhibiting anomalies should be replaced promptly.