ABB RELION 620 Series Technical Manual page 499

1MAC504801-IB E
620 series ANSI
Technical Manual
impedance measuring elements provide basic protection against the phase-to-phase short
circuit fault in all networks, regardless of the position of the neutral point.
The reach of phase-to-phase measuring elements is based on the loop impedance. The
reach is calculated using the equation:
R R
F F
Z ( R ) j X (
+ = + +
1 1
2 2
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R1 = Positive-sequence resistance from measuring point to fault location
X1 = Positive-sequence reactance from measuring point to fault location
RF = Physical fault resistance between phases, for example, arc resistance
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Figure 232: Fault loop impedance model for phase-to-phase impedance measuring
If the impedance measured falls in the region of operation, the trip timer activates the
PICKUP_Zx (x = 1...5) output for that zone. When the trip timer has reached the set
"Time delay Znx" (x = 1...5) value, the TRIP_Zx (x = 1...5) output is activated for that
zone.
Optional supervision function for phase-to-phase impedance measurement can be
enabled per zone by Ph Seq A check Znx (x = 1...5) setting. When Ph Seq A check Znx is
enabled, it is required that negative sequence current should exceed the Neg Seq value Znx
setting to release the phase-to-phase impedance measuring element.
Three-phase impedance measurement
A dedicated three-phase impedance measurement loop is activated on the receipt of the
three-phase release signal from the GFC module. The three-phase impedance measuring
element provides a basic protection for a three-phase short circuit fault. The measuring
element utilizes the positive-sequence quantities for a fault loop impedance measurement,
)
1
Section 4
Protection functions
(Equation 80)
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