slip is usually allowed before the generator-transformer unit is disconnected. A parameter
setting is available to take into account the circuit breaker opening time. If there are several
out-of-step relays in the power system, then the one which finds the center of oscillation
in its zone 1 should operate first.
Two current channels I3P1 and I3P2 are available in OOSPPAM function to allow the
direct connection of two groups of three-phase currents; that may be needed for very
powerful generators, with stator windings split into two groups per phase, when each
group is equipped with current transformers. The protection function performs a simple
summation of the currents of the two channels I3P1 and I3P2.
11.4.12.1 Verifying the settings
The test of the out-of-step protection function is made to verify that the trip is issued if the
following events happen.
• the impedance, seen by the function, enters the lens characteristic from one side and
leaves it from the opposite side
• the trip is issued according to the settings TripAngle and tBreaker
The tripping zone needs to be detected and confirmed. The test may be performed by
taking into account the following key points that are shown in Figure
40:
• the point RE (RE = Receiving End)
• the intersection between the line segment SE-RE and the X-line, which is defined
through the setting ReachZ1
• the point SE (SE = Sending End)
1MRK 504 165-UUS - Section 11
Testing functionality by secondary injection
Transformer protection RET670 2.2 ANSI 151
Commissioning manual
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