ABB RELION 620 Series Technical Manual page 500

Section 4
Protection functions
494
which increases the accuracy by reducing the influence of the line parameter asymmetry.
This is advantageous especially in case of non-transposed lines.
The reach of three-phase measuring element is based on the loop impedance. The reach is
calculated using the equation:
Z R ( R R ) j X (
+ = + +
F F
1 1
GUID-D42809E6-F16F-4C92-B8F4-8A0DAA47EE75 V1 EN
R1 = Positive-sequence resistance from measuring point to the fault location
X1 = Positive-sequence reactance from measuring point to the fault location
RF = Physical fault resistance per phase, for example, arc resistance
GUID-30E68FE6-CAFE-451B-BC2A-6EE28BEE9B8E V1 EN
Figure 233: Fault loop impedance model for three-phase impedance measuring
element
If the impedance measured falls in the operation region, 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 three-phase impedance measurement can be enabled
with the Ph Seq A check Znx (x = 1...5) setting. When Ph Seq A check Znx is enabled, the
positive-sequence current should exceed the Pos Seq value Znx setting to release the three-
phase impedance measuring element.
The memory voltage is used with the three-phase impedance measurement elements if the
positive-sequence voltage becomes too low. This assures the correct directional
measurement in case of the close-in three-phase faults, where the voltages on all three
phases are close to zero. The duration of the memory voltage is defined with the Voltage
Mem time setting. Default value is six cycles (= 100 ms, fn = 60 Hz).
)
1
1MAC504801-IB E
(Equation 81)
620 series ANSI
Technical Manual