With the widespread use of vacuum circuit breakers in the power industry, these devices offer several advantages, including minimal maintenance needs and high reliability. However, not all vacuum circuit breakers perform equally well. Some suffer from poor performance and may present various issues, while others are more prone to serious malfunctions that can lead to catastrophic failures, causing extensive power outages. Recently, I had the opportunity to assist an electrical engineer in troubleshooting a vacuum circuit breaker failure, which provided me with valuable hands-on experience and insights into comprehensive maintenance practices.
First, the issue of reduced vacuum in the bubble:
Fault Phenomenon:
Vacuum circuit breakers rely on the vacuum bubble to interrupt current and extinguish arcs. Unfortunately, there’s no direct way to qualitatively or quantitatively monitor the vacuum level, making this a hidden fault that poses significant risks.
Cause Analysis:
Poor quality materials or manufacturing processes in the vacuum bubble can create tiny leaks. Similarly, defects in the corrugated tube inside the bubble can lead to leaks after repeated operations. For split-type circuit breakers, especially those using electromagnetic operating mechanisms, longer operating links can impact switch synchronization, bounce, and overtravel, accelerating the rate of vacuum degradation.
Fault Hazard:
A decrease in vacuum level significantly impairs the breaker's ability to open and handle overcurrent conditions, drastically shortening its lifespan. In extreme cases, the switch could explode.
Solution:
During routine power-off maintenance, always use a vacuum tester to verify the vacuum level of the bubble. If the vacuum is compromised, replace the bubble and conduct tests for stroke, synchronization, bounce, and overtravel.
Precautions:
Select mature products from reputable manufacturers. Opt for integrated vacuum circuit breakers rather than split types. During inspections, watch for any external discharge around the bubble—if detected, the vacuum level is likelyä¸åˆæ ¼, and replacement should be immediate. Maintenance personnel must regularly perform characteristic tests to ensure optimal performance.
Second, the circuit breaker fails to trip:
Fault Phenomenon:
Depending on the root cause, the following issues may arise:
- The circuit breaker cannot be remotely tripped.
- Manual tripping is impossible.
- During an incident, the relay protection action occurs, but the breaker fails to separate.
Cause Analysis:
Possible causes include a broken trip circuit, malfunctioning opening coil, low operating voltage, increased coil resistance leading to reduced opening force, bent plunger pins causing jams, and severe deformation of the opening lever.
Fault Hazard:
If tripping fails during an accident, the situation escalates, expanding the scope of the outage.
Solution:
Check the integrity of the trip circuit, inspect the coil for damage, measure coil resistance, examine plunger pins for deformation, verify operating voltage, and replace copper pins with steel ones to prevent bending.
Precautions:
On-site electricians should immediately investigate any dimming of the trip/close indicator lights. Maintenance personnel must measure coil resistance during power-off checks and inspect plungers for deformation. Additionally, low-voltage switching tests should be conducted to ensure reliable breaker performance.
Third, energy storage circuit failure in the spring-operated mechanism:
Fault Phenomenon:
After closing, the breaker cannot open. Furthermore, the energy storage motor continues running, sometimes overheating and damaging the coil.
Cause Analysis:
Improper placement of the travel switch may leave the closing spring under-stored, preventing timely disconnection of the motor power. Conversely, a misaligned switch may keep the motor running after storage completion. Damage to the travel switch can also prevent proper motor shutdown.
Fault Hazard:
Inadequate energy storage can render the breaker incapable of responding to faults, leading to overstepped incidents and broader outages. A damaged motor renders the breaker inoperable.
Solution:
Adjust the travel switch position to ensure accurate motor disconnection. Replace faulty switches promptly.
Precautions:
Operators should monitor the energy storage indicator during operation to assess readiness. After maintenance, perform two closing operations on-site to confirm proper functionality.
Fourth, inconsistent opening/closing times and large bounce values:
Fault Phenomenon:
This is a hidden fault requiring measurement via a characteristic tester for accurate data.
Cause Analysis:
Poor mechanical performance of the breaker leads to excessive bounce after numerous operations. For split-type breakers, large distances between operating rods can cause phase deviations, leading to inconsistent timing and high bounce values.
Fault Hazard:
Inconsistent timing or excessive bounce seriously affects the breaker’s ability to open and handle overcurrent, shortens its lifespan, and may cause explosions in severe cases. Since this is a hidden fault, it poses a heightened risk.
Solution:
Adjust the length of the three-phase insulated tie rods to bring synchronization and bounce within acceptable limits. If adjustment proves insufficient, replace the faulty vacuum bubble and re-adjust until data meets standards.
Precautions:
Given the complexities of split vacuum breakers, integrated models are recommended. Regular maintenance should include characteristic testing using a tester to address issues early. Providing a suitable working environment for the equipment ensures safe and reliable operation of the vacuum circuit breaker.