Out-Of-Step Protection Oosppam (78); Identification; Application - ABB RELION 670 SERIES Applications Manual

Line distance protection

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1MRK 506 369-UUS -

Line distance protection REL670 2.2 ANSI

Application manual

Out-of-step protection OOSPPAM (78)

Function description

Out-of-step protection

Under balanced and stable conditions, a generator operates with a constant rotor (power)

angle, delivering an active electrical power to the power system, which is equal to the

mechanical input power on the generator axis, minus the small losses in the generator. In

the case of a three-phase fault electrically close to the generator, no active power can be

delivered. Almost all mechanical power from the turbine is under this condition used to

accelerate the moving parts, that is, the rotor and the turbine. If the fault is not cleared

quickly, the generator may not remain in synchronism after the fault has been cleared. If

the generator loses synchronism (Out-of-step) with the rest of the system, pole slipping

occurs. This is characterized by a wild flow of synchronizing power, which reverses in

direction twice for every slip cycle.

The out-of-step phenomenon occurs when a phase opposition occurs periodically between

different parts of a power system. This is often shown in a simplified way as two

equivalent generators connected to each other via an equivalent transmission line and the

phase difference between the equivalent generators is 180 electrical degrees.

Impedance protection

identification

ANSI/IEEE C37.2

device number