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rotor earth fault/ single phase protection of slipring motor


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#1 asgkrishnan

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Posted 22 February 2006 - 03:35 PM

;p; Is there any practical solution for providing protection to a slipring induction motor in case of rotor earth fault or rotor lead cutinside motor. Can anybody help me?

#2 marke

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Posted 22 February 2006 - 06:13 PM

Hello asgkrishnan

A am not aware of any special rotor protection relays. The difficulty is that the source of the energy is within the rotor so you can not put protection between the source and the rotor within the rotor circuit.
If there is a problem in the rotor, this will be reflected though to the stator circuit and I expect that good stator protection will also provide reasonable rotor protection as well.

Best regards,

#3 asgkrishnan

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Posted 24 February 2006 - 02:37 AM

Thank you sir. I tried putting CTs (connected with motor protection relay) in the rotor ckt and found not working properly as the frequency is very less near to full speed. Is it possible to function with a DC relay and DCCT in rotor. I feel it may work since rotor current is almost dc during it full speed.

#4 marke

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Posted 24 February 2006 - 06:47 AM

Hello asgkrishnan

The frequency of the rotor current depends on the rotor slip. At full speed, the slip is close to zero, so the frequency is also close to zero.
I am not sure what you will achieve by measuring the rotor current. This will not show up a shorted turn in the rotor, or a short to earth in the rotor circuit.
If there is a problem which causes the rotor current to go higher than it should, the stator current will also go higher than it should.
I believe that stator protection should be sufficient.

Best regards,




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