Vacuum Circuit Breaker

Testing
● Visual Inspection
The visual check is the simplest and primary one. Various parts such as drive insulators and molded pole unit support can be checked visually for dirt and cracking. Similarly, the control circuit parts such as wiring and terminals can also be checked for their intactness. For testing dirt and dust in the operating mechanism, a visual check is there. Sometimes, along with visual inspection, one can also feel and sense to inspect the parts e.g., for checking the tightness of hardware or operating mechanism.
● Vacuum Interrupter Integrity Test
The reliability of a vacuum circuit breaker depends upon the integrity of the vacuum and the internal dielectric strength. For checking both of them, vacuum interrupter testing is arranged. The vacuum circuit breaker testing procedure is also known as a hipot test because a high potential is applied during the testing. This one-minute ac high potential test is used to check the insulation integrity from the main circuit to ground, from the control circuit to ground, and between main circuit terminals. A successful withstand indicates the good functioning of the vacuum interrupters whereas a break-down indicates that there is a defective interrupter or interrupters that needed to be repaired or replaced.
● Mechanism Check
The mechanism check involves visual inspection of the mechanism for any loose parts such as rings, bolts, and others. The other parts of mechanism check can include measurement check, functional check, operational check, or a combination of these. The measurement check is required for the inspection of vacuum interrupters for the visibility of three contact erosion indicators and contact wipe measurement. For checking the smooth functioning of a motor, a functional test is required. Similarly, for excessive wearing or deformation of the operating mechanism, both visual and operational checks are required. Sometimes, for the checking of the correct and smooth operation of certain parts, closing, tripping of the circuit breaker, or manual charging is also employed.

Insulation
This is one of the simplest maintenance techniques. Insulation maintenance applies to the cleaning of all the insulation surfaces. Any soft cloth like a dry lint-free cloth or dry paper towel can be used to wipe off the dust from the insulation surfaces to ensure their smooth functioning. If wiping is unable to remove dust properly, distilled water or a mild solvent can be used for the purpose of removing dirt and dust. Once wiped, make sure that all the surfaces have completely dried up before placing the circuit breaker in service. Inspect for any damage to the insulation and ensure that all the wires are tightly connected before putting the circuit breaker back in use.

Lubrication
Proper lubrication is required periodically to ensure the overall smooth and correct functioning of all the parts of a vacuum circuit breaker and VCB maintenance. The gap between relubrication depends on the frequency of the circuit breaker used. Generally, it is suggested to go for relubrication once a year. For lubrication, a drop of light machine oil can be used. After lubrication, the circuit breaker needs to be operated several times manually and electrically so that the oil is absorbed into the parts properly. Roller bearings come packed with a high-quality slow oxidizing grease from the vcb manufacturer itself. Hence, they should be lubricated only when needed.