Enhanced reach loop
Max current Loop selected Voltage phasor Current phasor
IL1 L1-E UL1E-U0 IL1
IL2 L2-E UL2E-U0 IL2
IL3 L3-E UL3E-U0 IL3
If the currents are equal, L1-E loop has higher priority than L2-E and
L2-E loop has higher priority than L3-E. UL1E, UL2E, UL3E are
three phase–to–earth voltages and IL1, IL2, IL3 are three phase
currents and U0 is zero sequence voltage.
To measure correct impedance for phase-to-phase faults on HV side of the generator
transformer, it is recommended that EnhancedReach option (phase-to-earth loop with
maximum current loop) is used.For three-phase faults on HV side, phase-to-phase
loop measures correct impedance.
Under impedance function is not intended to operate for phase-to-ground fault in the
generator. To prevent such an operation, the phase-to-earth voltage in
EnhancedReach is compensated with zero sequence voltage.
8.9.2.4 Zone 3 operation
Zone 3 covers the HV side of the transformer, interconnecting station bus to the
network and outgoing lines. Within its operating zone, the tripping time for this relay
should be coordinated with the longest time delay of the phase distance relays on the
transmission lines connected to the generating substation bus. It is normally set to
about 80% of the load impedance considering maximum short time overload on the
generator.
Zone 3 provides protection for phase-to-earth, phase-to-phase and three phase faults
on the HV side of the system. Hence, all these faults can be detected using three phase-
to-phase loops or Enhanced reach loop similar to zone 2. These options can be selected
in the function and their operation is same as the operation of zone 2.
8.9.2.5 CT and VT positions
Voltage transformer is located at the terminals of the generator, but current
transformer can be located either at neutral side of the stator winding or at the
terminals of the generator.
If the current transformer is located at the neutral side of the generator winding, the
forward reach will be of the generator, transformer and connected power system
impedance. If the current transformers are located at the terminal of the generator
always the forward reach is only generator impedance and reverse reach comprises of
transformer impedance and the connected transmission lines impedance.
Section 8 1MRK 502 071-UEN -
Impedance protection
312 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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