Impedance Protection - ABB REG650 Product Manual

Generator protection REG650
Product version: 1.3
An open CT circuit condition creates unexpected operations for
Generator differential protection under the normal load
conditions. It is also possible to damage secondary equipment
due to high voltage produced from open CT circuit outputs.
Therefore, it may be a requirement from security and reliability
points of view to have open CT detection function to block
Generator differential protection function in case of open CT
conditions and at the same time produce the alarm signal to the
operational personal to make quick remedy actions to correct
the open CT condition.
Generator differential protection GENPDIF is also well suited to
generate fast, sensitive and selective fault clearance, if used to
protect shunt reactors or small busduct.

5. Impedance protection

Power swing detection ZMRPSB
Power swings may occur after disconnection of heavy loads or
trip of big generation plants.
Power swing detection function ZMRPSB is used to detect
power swings and initiate block of all distance protection zones.
Occurrence of earth-fault currents during a power swing
inhibits the ZMRPSB function to allow fault clearance.
Underimpedance protection for generators and transformers
ZGCPDIS
The underimpedance protection for generators and
transformers ZGCPDIS, has the offset mho characteristic as a
three zone back-up protection for detection of phase-to-phase
short circuits in transformers and generators. The full scheme
three zones have independent measuring phase-to-phase
loops and settings that gives high flexibility for all types of
applications.
All three zones can be individually definite time delayed.
A load encroachment characteristic is available for the third
zone as shown in figure 4.
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jX
Operation area Operation area
Operation area
No operation area No operation area
IEC07000117-2-en.vsd
IEC07000117 V2 EN
Figure 4. Load encroachment influence on the offset mho Z3
characteristic
Loss of excitation LEXPDIS
There are limits for the low excitation 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 becomes too low.
The impedance measurement is used for LEXPDIS function. Its
operating characteristic is designed as two zone, offset mho
circles and a directional element restrain line.
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.
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.
Consideration can be taken to the breaker trip time by
parameter setting. If there are several out-of-step relays in the
1MRK 502 050-BEN B
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