Out of Step Protection

The out-of-step element provides out of step (loss-of-synchronism

or pole slip) tripping function for generators. The element is simplified

using a single blinder operating characteristic with an offset

mho supervisory. It is easy to apply based on IEEE/ANSI C37.102

guidelines, and IEEE PES PSRC tutorial on generator protection.

The purpose of the supervisory mho is to prevent operation on

stable swings that pass through both blinders and outside the mho

characteristic. In addition, the out-of-step tripping feature allows

“MHO EXIT” trip mode to reduce stresses on the circuit breaker.

Stator Thermal Protection

The 889 provides thermal overload protection as per IEC 60255-8

to prevent generator damage caused by generator overheating.

The 889 can be configured to trip the generator offline when the

generator’s thermal limits are reached, or close an Alarm contact

that signals operations personnel to take appropriate actions.