Mitigating the effects of arcs in M.V. switchgear
An internal arc in MV switchgear results from an insulation failure between conductor phases or between conductor phases and earth. The effects of these arcs hold significant risks to the safety of operators and members of the public who may have access to equipment installations, and to the electrical plant health and electrical plant availability.
To prevent these insulation failures newer generation MV switchgear standards include more onerous type test requirements to ensure the adequate dielectric design and performance of the switchgear. However, as the risk cannot be completely eliminated, internal arc classification (IAC) could be assigned to state the behaviour in case of failure, and the tested parameters. Specific functions may also be added, designated to mitigate the effects of internal arc faults, by reducing the available fault current, the arc duration and/or the exposure of personnel to arc effects. A complete mitigation strategy for the arc effects in MV switchgear was found to be the implementation of internal arc resistant switchgear in combination with active and passive arc mitigation systems. However, its installation will remain a choice of the user, based on applying sound engineering principles to ensure equipment and people safety as far as reasonable possible.
Commercially available techniques reducing of the arc duration are reviewed to provide end users with useful engineering considerations and guidance on its practice, being achieved by sensors to detect the arc event and activities to accelerate circuit-breaker operation or to activate a fast-acting switch transferring the arc current to a commutation circuit.
Consideration is also given to the possibility of validation for all these systems, and it appears to be rather challenging, as it could involve various functions and only the global behaviour is really significant.
File Size: 4,9 MB
Pages NB: 75
WG (TF): WG B3.37