Synchronous motor out of step relay
Synchronous motor out of step relay
(OP)
Hi,
I want to replace an Out of Step Relay for Motors "MFOS 24" from Alstom.
I'am looking for a relay with the latest technology.
I can only find numerical protection relays who monitor the reactive power or the power factor of the motor to perform a motor" pull out" or "out step" protection.
Can anyone advice a recent motor out of step relay?
Thanks for your help





RE: Synchronous motor out of step relay
RE: Synchronous motor out of step relay
I'am wondering if i can use the loss of excitation protection of a generator protection relay to perform an motor out of step protection.
I'am speaking about the loss of exictation protection with 2 mhos circles.
If not why ?
RE: Synchronous motor out of step relay
RE: Synchronous motor out of step relay
What size is the motor and what is it driving?
RE: Synchronous motor out of step relay
RE: Synchronous motor out of step relay
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If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor out of step relay
As i see that most motor numerical protection relay perform the out of step protection with the Power factor protection 55, i was wondering if i can use a transducer (with fast cycle time) measuring the motor power factor to perform this protection.
Note that i have only a single phase CT and single phase VT to perform the protection which eliminates most numerical relays.
The trip coming from the transducer would be inhibited until the motor is running at full speed.
This would be equivalent to the PF protection in the MICOM P243.
Hereunder an extract from the IM:
"Upon loss of synchronism a heavy current at a very low power factor is drawn from the supply. The P24x is able to monitor this change in power factor when the motor pole slips, thus allowing appropriate action to be taken. If the power factor passes under a defined threshold for a defined time, a trip is generated."
Setting Guidelines :
The ability of a motor to run at a low power factor will be design dependent.
For a unity power factor machine, the following settings will be typical :
power factor = 0.9,
time delay = 50 ms,
drop-off time delay = 1 or 2 seconds above the start time of the machine.
Do you have any comment on 50ms time delay? should it be longer?
Thanks for your help
RE: Synchronous motor out of step relay
http://www.selinc.com/SEL-700G/