Voltage-controlled time-multiplier protection 1

[RichardTaylor]

Does anyone out there have any experience of the application of Vtm (Voltage-controlled time-multiplier) protection on a high Voltage distribution system?

I believe the system is based on overcurrent relays which are arranged to reduce their time multipler settings as the system Voltage falls towards a fault.

I am particularly wondering how well the system would perform applied to a resistance-earthed 11kV system under earth-fault conditions.

 

[dpc]

Voltage-restrained or voltage-controlled overcurrent relays are typically applied as back-up protection for generators for sustained faults. The voltage restraints allows the overcurrent pickup to be set below the normal full load current of the generator. This is necessary because the synchronous reactance of the generator is typically greater than 100% meaning that the sustained fault current will be less than the normal generator full load current (in the absence of any field forcing).

I've rarely seen these relays used for other applications and I don't really see much benefit to using one in the situation you describe. But I've been wrong before....