ABB RELION 670 Series Product Manual page 31

Transformer protection RET670 2.1 IEC
clearing on the adjacent power lines and other primary
elements.
Pole slip protection PSPPPAM
The situation with pole slip of a generator can be caused
by different reasons.
A short circuit may occur in the external power grid,
close to the generator. If the fault clearing time is too
long, the generator will accelerate so much, that the
synchronism cannot be maintained.
Undamped oscillations occur in the power system,
where generator groups at different locations, oscillate
against each other. If the connection between the
generators is too weak the magnitude of the oscillations
will increase until the angular stability is lost.
The operation of a generator having pole slip will give
risk of damages to the generator, shaft and turbine.
• At each pole slip there will be significant torque
impact on the generator-turbine shaft.
• In asynchronous operation there will be induction of
currents in parts of the generator normally not
carrying current, thus resulting in increased heating.
The consequence can be damages on insulation and
stator/rotor iron.
The Pole slip protection (PSPPPAM) function shall detect
pole slip conditions and trip the generator as fast as
possible if the locus of the measured impedance is
inside the generator-transformer block. If the centre of
pole slip is outside in the power grid, the first action
should be to split the network into two parts, after line
protection action. If this fails there should be operation
of the generator PSPPPAM in zone 2, to prevent further
damages to the generator, shaft and turbine.
Pole slip protection PSPPPAM
Sudden events in an electric power system such as large
changes in load, fault occurrence or fault clearance, can
cause power oscillations referred to as power swings. In
a non-recoverable situation, the power swings become
so severe that the synchronism is lost, a condition
referred to as pole slipping. The main purpose of the
pole slip protection (PSPPPAM) is to detect, evaluate,
and take the required action for pole slipping
occurrences in the power system.
Out-of-step protection OOSPPAM
The out-of-step protection OOSPPAM function in the IED
can be used for both generator protection and as well
for line protection applications.
The main purpose of the OOSPPAM function is to detect,
evaluate, and take the required action during pole
slipping occurrences in the power system.
ABB
SEMOD143246-4 v4
SEMOD143246-17 v7
GUID-BF2F7D4C-F579-4EBD-9AFC-7C03296BD5D4 v7
The OOSPPAM function detects pole slip conditions and
trips the generator as fast as possible, after the first
pole-slip if the center of oscillation is found to be in
zone 1, which normally includes the generator and its
step-up power transformer. If the center of oscillation is
found to be further out in the power system, in zone 2,
more than one pole-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.
Phase preference logic PPLPHIZ
The optional phase preference logic main purpose is to
provide a selective tripping for cross-country faults in
isolated or high impedance-earthed networks.
Underimpedance protection for generators and
transformers ZGVPDIS
The under impedance protection is a three zone full
scheme impedance protection using offset mho
characteristics for detecting faults in the generator,
generator-transformer and transmission system. The
three zones have fully independent measuring loops and
settings. The functionality also comprises an under
voltage seal-in feature to ensure issuing of a trip even if
the current transformer goes into saturation and, in
addition, the positive-sequence-based load
encroachment feature for the second and the third
impedance zone. Built-in compensation for the step-up
transformer vector group connection is available.
5. Current protection
Instantaneous phase overcurrent protection PHPIOC
The instantaneous three phase overcurrent function has
a low transient overreach and short tripping time to
allow use as a high set short-circuit protection function.
Four-step phase overcurrent protection OC4PTOC
The four step three-phase overcurrent protection
function OC4PTOC has an inverse or definite time delay
independent for step 1 to 4 separately.
1MRK 504 155-BEN F
SEMOD153619-5 v2
GUID-5D0E6F04-8B60-4F12-8DA6-7043BE09A3CC v5
M12910-3 v12
M12846-3 v16
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