- VI reaches its wear limits: The VI has a set of soft copper alloy contacts that are mechanically shocked every time the breaker is opened and closed. When no current flows, the damage to the contacts is caused primarily by the mechanical shock.
- Internal arc flashover caused by metal vapor and sputtering material being deposited on the inside of the canister. This is especially bad if the material is deposited on the inside of the ceramic shell as it greatly reduces the insulation quality of the shell. Since the shell must be able to withstand the recovery voltage caused by an arc interruption, insulation failure of the shell can cause a catastrophic mechanical failure of the VI.
- loss of vacuum due to mechanical failure of the bellows, pinch tube, or a manufacturing defect. This type of failure is quite often related to the number of operations multiplied by the number one killer on any VI – torsion exerted on the bellows.
- leak rate: The leak rate was checked at the factory however, the leak rate can be greatly increased by improper installation, failure of components, or damage during maintenance procedures.
Photo show a 5kv vacuuminterrupter fail for loss of vacuum.