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MV system earthing

MV system earthing

MV system earthing

(OP)
References like IEEE recommend low resistance earthing of MV systems. In case of motor power supply switchboards, the recommendation is to limit the earth fault currents to ~300A.
From the point of preventing the core burning in motors in case of earth faults, the motor vendors are recommending the current to be limited to 30A.
Are there 3.3/6.6/11kV systems in service with earth fault currents limited to below 50A!
Appreciate sharing of experiences!

RE: MV system earthing

Thermal build-up depends on the length of time the current will be sustained. Protection settings may have different objective in different applications. In some motor itself is the most precious, in some motor is sacrificial.

Rafiq Bulsara
http://www.srengineersct.com

RE: MV system earthing

I also think that 300A is probably meant for the system or feeder level (which feeding several motors and other loads) protection and 30A is for an individual motor branch circuit.

Rafiq Bulsara
http://www.srengineersct.com

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