Synchronous Motors out of step relay

[hlrl]

Hi,
Anyone familar with synchronous motor out-of-step protection relay GTM7111.
This relay has the following settings:
"S" setting which varies from 20% to 80% of Sq root(3)xInxV.
"Time delay" setting of 0.1 to 0.5sec.

Need to understand the concept of the PQ diagram.
Does anyone has articles on the PQ diagram which explain the concept of setting the out-of-step protection relay for synchronous motors.

Thanks.

rl.

 

[swn1]

Most vendors call this function "pull out" when it is applied to a motor, the "out of step" terminology is usually seen when it is applied to generators.

The settings are seldom critical. The relay's job is to trip out the field and/or the main supply when the motor "pulls out of sync". This will happen either due to a sudden load torque increase or a loss of excitation. Or, in theory, a sudden increase in supply frequency.

In most motor applications none of these things will happen in a non-catastrophic way, so the settings aren't critical.

That said, the PQ diagram plots the locus of operating points of them machine with real power on the horizontal axis and reactive power on the vertical. In generator applications the machine vendor should supply a "capability curve" showing allowable operating region in the PQ plane.

Basler has better-than-average documentation online for these concepts.