ABB RELION RET670, Applications Manual

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Figure 253: Zone characteristics and typical power system model
The settings of all the zones is provided in terms of percentage of impedance based on
current and voltage ratings of the generator.
8.21.2.2 Zone 1 operation
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Zone 1 is used as fast selective tripping for phase-to-phase faults and three–phase
faults in the generator, on the terminal leads and delta side of generator transformer.
Since generator is high impedance grounded, the fault current for phase-to-ground
faults will be too low and impedance protection is not intended to operate for these
faults.
The measuring loops used for zone1 are given below.
Zone 1 measuring loops for phase-to-phase faults and three–phase faults on the
primary side of the generator transformer are:
Sl.No Phase-to-phase loop Voltage phasor Current phasor
1 A–B VAB IAB
2 B–C VBC IBC
3 C–A VCA ICA
VAB, VBC, VCA are three phase-to-phase voltages. IAB, IBC, ICA are
the three phase-to-phase currents.
For this application the zone 1 element is typically set to see 75% of the transformer
impedance.
8.21.2.3 Zone 2 operation
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Zone 2 can be used to cover up to the HV side of the transformer and the HV bus bar,
and is usually set to cover 125% of the generator transformer impedance. The time to
trip must be provided in order to coordinate with the zone 1 element on the shortest
outgoing line from the bus.
Two options are provided for measuring loops used for zone 2, which is set by the user.
The measuring loops used for zone 2 with different options are:
Phase-to-phase loops
Section 8
1MRK 504 163-UUS A
Impedance protection
504 Transformer protection RET670 2.2 ANSI
Application manual