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.
Out-of-step protection OOSPPAM
GUID-BF2F7D4C-F579-4EBD-9AFC-7C03296BD5D4 v7
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.
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.
Loss of excitation LEXPDIS
SEMOD151269-4 v8
There are limits for the under-excited operation of a
synchronous machine. A reduction of the excitation current
weakens the coupling between the rotor and the stator. The
machine may lose the synchronism and start to operate like
an induction machine. Then, the reactive power consumption
will increase. Even if the machine does not loose synchronism
it may not be acceptable to operate in this state for a long
time. Reduction of excitation increases the generation of heat
in the end region of the synchronous machine. The local
heating may damage the insulation of the stator winding and
the iron core.
To prevent damages to the generator it should be tripped
when excitation is lost.
Sensitive rotor earth fault protection, injection based
ROTIPHIZ
GUID-9D60105D-44C8-4FB1-AD63-C4D3631BC99E v2
The sensitive rotor earth fault protection (ROTIPHIZ) is used
to detect earth faults in the rotor windings of generators.
ROTIPHIZ is applicable for all types of synchronous
generators.
To implement the above concept, a separate injection box is
required. The injection box generates a square wave voltage
signal at a certain preset frequency which is fed into the rotor
winding.
The magnitude of the injected voltage signal and the resulting
injected current is measured through a resistive shunt located
within the injection box. These two measured values are fed
to the IED. Based on these two measured quantities, the
protection IED determines the rotor winding resistance to
ground. The resistance value is then compared with the
preset fault resistance alarm and trip levels.
The protection function can detect earth faults in the entire
rotor winding and associated connections.
Requires injection unit REX060 and a coupling capacitor unit
REX061 for correct operation.
100% stator earth fault protection, injection based STTIPHIZ
GUID-A9BF9D69-2179-441C-A6C7-69EF0F55DD61 v2
The 100% stator earth-fault protection STTIPHIZ is used to
detect earth faults in the stator windings of generators and
motors. STTIPHIZ is applicable for generators connected to
the power system through a unit transformer in a block
connection. An independent signal with a certain frequency
different from the generator rated frequency is injected into
the stator circuit. The responce of this injected signal is used
to detect stator earth faults.
To implement the above concept, a separate injection box is
required. The injection box generates a square wave voltage
signal which for example can be fed into the secondary
winding of the generator neutral point voltage transformer or
grounding transformer. This signal propagates through this
transformer into the stator circuit.
1MRK 502 068-BEN D
Generator protection REG670 2.1 IEC
Product version: 2.1
20
ABB
