ABB REG670 Applications Manual page 315

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
the generator transformer. Zone 2 can be used to cover generator transformer and
power plant's substation bus-bar. Zone 3 can be used to cover power system faults.
The under impedance protection is provided with undervoltage detection feature in
order to provide the seal-in for the impedance based trip. Additionally, it is provided
with load encroachment feature in order to avoid tripping of the protection during
heavy load conditions. The load encroachment functionality is based on the positive
sequence components of voltage and current.
Characteristics of backup impedance protection
Characteristics of zone 1, zone 2 and zone 3 are shown in figure 165. All zones have
offset mho characteristics with adjustable reach in forward and reverse direction. The
characteristic angle for all three zones is common and adjustable. A load
encroachment blinder feature is provided for zone 2 and zone 3.
Protection designed to operate for below types of faults
Faults in the generator, generator terminal connections to the step-up transformer and
in the low voltage (LV) side of the generator step-up transformer are:
1. Phase-to-phase faults in generator
2. Three-phase faults in generator
3. Phase-to-phase faults in the LV winding of the generator transformer or inter-
connecting bus or cables
4. Three-phase faults in the LV winding of the generator transformer or inter-
connecting bus or cables
Faults in the system in the high voltage (HV) side of generator transformer are:
1. Phase-to-earth faults in the HV side of generator transformer and in the power
system
2. Phase-to-phase faults in the HV side of generator transformer and in the power
system
3. Phase-phase-earth faults in the HV side of generator transformer and in the power
system
4. Three-phase faults in the HV side of generator transformer and in the power
system
Section 8
Impedance protection
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