Vacuum circuit breaker (VCB) is a vital part in medium and high voltage electrical systems, in which vacuum is used as the arc extinguishing medium, and it has the capability of fault current cutoff in the circuit effectively. The status of the vacuum inside a vacuum circuit breaker should be checked to guarantee normal working of it and ensure system safety. This article describes how to check the vacuum inside a vacuum circuit breaker effectively.
Why to check the vacuum?
The vacuum within the VCB acts as the insulating media. The generation of vacuum degrades due to the following reasons with time: Leakages – Mechanical wear and material fatigue caused leakages, Aging of internals: Generation of gas, thereby reducing insulation performance, External environment: Such as moisture or corrosion has affected the seal.
If the level of vacuum gets disturbed, it will lead to failure of the circuit breaker not to extinguish the arc, which leads to serious damages or failure in the system.
VCB Vacuum Level Checking Methods
● Visual Check
Do a simple external check. The housing of the circuit breaker should be inspected for any clear indication of damage or leakage that would indicate loss of seal in the vacuum chamber.
● HiPot tester for vacuum integrity test
Purpose: This test will ensure that the VCB maintains proper insulation in its vacuum circuit breaker.
Procedure:
Disconnect the circuit breaker from the system and ensure it is isolated.
Using a HiPot tester, apply high voltage between the contacts of the circuit breaker.
Monitor leakage current. If the current exceeds the acceptable range, it indicates a loss of vacuum.
Safety tip: The voltage always should be limited within the manufacturer tolerance in order to avoid any damage to the circuit breaker.
● Magnetic field or Penning effect test
Purpose: Indirect vacuum pressure measurement through gas ionization.
Procedure:
Create a magnetic field of predetermined value around the circuit breaker.
Provide a low voltage arc to measure the ionization level of the gas.
The intensity of ionization current provides the level of vacuum. The lower ionization current means better vacuum.
● Mechanical inspection
Although it is not a direct measurement of vacuum, the physical condition of the VCB seals and housing can provide some clues. Cracks, rust, or visible wear may indicate a possible vacuum leak.
Combine this with electrical testing for accurate results.
● Portable vacuum measuring equipment
Specialized vacuum measuring equipment can be connected to the VCB to directly measure the pressure inside the vacuum chamber. These tools are very accurate but usually require professional operation.
Following are some of the signs of vacuum degradation that one should look for during routine inspections:
Longer arc extinguishing time: If the arc extinguishing time is longer, it may indicate that the vacuum level is impaired.
Abnormal switching behavior: Unexpected tripping or contact welding may be caused by insufficient vacuum.
Visible damage or leakage: Cracks in the circuit breaker or corrosion around the seals may indicate vacuum loss.
● Inspection frequency
Inspection for vacuum circuit breakers is normally based on usage conditions of the equipment and recommendations provided by the manufacturer. Generally, during normal operation of the power system, basic inspections shall be done at least once every year. Where in case of more severe environments, they may require higher frequency.
● Safety precaution
De-energized operation: Before the inspection is done, the circuit breaker should be de-energized and appropriate isolation with safety provided.
Professional operation: Some tests require professional technicians and special equipment. Improper operation may cause equipment damage or personal injury.
Follow the Code: The vacuum circuit breaker shall be inspected and maintained in accordance with industry standards and manufacturer guidelines.
How often to check the vacuum?
Routine: They should be annually tested or at routine periods specified by the manufacturer for maintenance.
After a severe fault: If VCB interrupts a high current earth fault, then vacuum must be checked immediately because such excessive stress will degrade the vacuum.
Before commissioning: Always vacuum integrity must be checked during installation or commissioning.
Best Practices to Maintain VCB Vacuum
Regular Maintenance: Early detection of impending problems is done by scheduling tests and inspections.
Proper storage: The spare VCBs should be stored in a dry and clean environment to protect the vacuum chamber.
Use manufacturer-specified tools: Always use recommended test equipment and follow the manufacturer’s recommendations.
Monitor operation: Noise or raised temperature during switching is some of the abnormal operating conditions that shall be monitored.
Slutsats
It is important to check the vacuum in a vacuum circuit breaker for both equipment reliability and safety. Testing the vacuum integrity by HiPot test, magnetic field test, or portable equipment provides confidence that potential failures can be avoided and you can extend equipment life. Schedule vacuum checks within your routine maintenance and take immediate action if you detect any problems.
Where the test results are indecisive or losses of vacuum are suspected, consultation with qualified technicians or contact with the VCB manufacturer is recommended to help troubleshoot the problems. Proper maintenance of the VCB can save time and money while avoiding long-term downtime.
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