Motor Diff with Variable Speed Drive
Motor Diff with Variable Speed Drive
(OP)
Hi
We are specifying medium volatge induction motors (6.6kV) with biased differential protection above 1500kW. However some of these motors will be supplied by Varibale Speed Drives. A Supplier is saying that motors driven by VSDs should not be protected by differential protection because at low speed, the CTs will saturate and the diff protection would trip the motor spuriously. Does anyone has experience in this or ever installed Diff prot on VSD motors ?
Thanks
We are specifying medium volatge induction motors (6.6kV) with biased differential protection above 1500kW. However some of these motors will be supplied by Varibale Speed Drives. A Supplier is saying that motors driven by VSDs should not be protected by differential protection because at low speed, the CTs will saturate and the diff protection would trip the motor spuriously. Does anyone has experience in this or ever installed Diff prot on VSD motors ?
Thanks





RE: Motor Diff with Variable Speed Drive
But standard CT:s won't work well. That is true.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Motor Diff with Variable Speed Drive
RE: Motor Diff with Variable Speed Drive
The reason is that the volt-seconds area that the motor sees is quite constant, independent of motor speed. That does not apply to CT:s since you can have high current at low frequencies, which saturates the core. That does not happen in voltage transformers.
Then, another question is: is it current or voltage unbalance you want to check?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Motor Diff with Variable Speed Drive
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington