Out-Of-Step Protection Oosppam (78) - ABB RELION 670 Series Applications Manual

1MRK 511 364-UUS A
7.2

Out-of-step protection OOSPPAM (78)

7.2.1 Identification
Function description
Out-of-step protection
7.2.2 Application
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.
Synchronous Synchronous
machine 1 machine 1
SM1 SM1
E1 E1
E1 E1
ANSI10000107 V3 EN-US
Figure 47: The center of electromechanical oscillation
The center of the electromechanical oscillation can be in the generator unit (or generator-
transformer unit) or outside, somewhere in the power system. When the center of the
Application manual
IEC 61850
identification
OOSPPAM
V, I
Center of oscillation
IEC 60617
identification
<
Synchronous Synchronous
machine 2 machine 2
SM2 SM2
Voltages of all phases
E2 E2
to ground are zero in
the center of
oscillation
ANSI10000107_3_en.vsd
Impedance protection
GUID-8321AC72-187C-4E43-A0FC-AAC7829397C3 v1
GUID-BF2F1533-BA39-48F0-A55C-0B13A393F780 v2
ANSI/IEEE C37.2
device number
78
GUID-11643CF1-4EF5-47F0-B0D4-6715ACEEC8EC v6
E2 E2
Section 7
103