out of step protection

[rajendrarohra1978]

Hi!

We have ABB RXPD 21H OUT OF STEP RELAY ( LOSS OF EXCITATION).The relay is used for 19.3 MW synchronous motor. From last two months the machine is tripped two times due to this relay activated. Though the parameters such as load & voltage are within range. Please can anyone highlight the reason behind this tripping. Once machine tripped it is smoothly started in first start.

Can there be any issue with the Relay itself. The machine is in service since last 17 years but running from time to time depending on plant requirement.

thanks,

 

[waross]

I would first check all connections in the wiring TO the relay.
Next check the excitation wiring for bad connection.
Third consider a faulty relay.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[pwrengrds]

Look at the relay settings to see if the settings are correct. From the manual it looks like a directional over current relay.

Could the motor be under excitated or have a problem with the exciter, where it really is slipping poles?

 

[marks1080]

It only takes about 20 minutes to test the relay. If you wait for the unit to trip again, there should be no problems getting an outage either

If the relay is tripping, it's telling you there is a problem on the primary system. Sure, the relay could be bad... the wiring could be bad... but check what the relay is telling you first.