ABB Relion 670 series, Technical Manual

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where:
IA, IB, IC are fundamental frequency phasors of three individual phase currents.
a is so called operator which gives a phase shift of 120 deg, that is, a = 1∠120
deg
a
2
similarly gives a phase shift of 240 deg, that is, a
2
= 1∠240 deg
The phasor magnitude is used within the NS4PTOC (4612) protection to compare it with the set
operation current value of the four steps ( Pickup1, Pickup2, Pickup3 or Pickup4). If the negative
sequence current is larger than the set operation current and the step is used in non-directional
mode a signal from the comparator for this step is set to true. This signal, without delay, activates
the output signal PU_STx (x=1 - 4) for this step and a common PICKUP signal.
8.5.7.2 Internal polarizing facility of the function
GUID-B00FE98B-F269-4F1B-AC03-68250798851B v3
A polarizing quantity is used within the protection to determine the direction to the fault
(Forward/Reverse).
Four step negative sequence overcurrent protection NS4PTOC (4612) function uses the voltage
polarizing method.
NS4PTOC (4612) uses the negative sequence voltage -V2 as polarizing quantity V3P. This voltage is
calculated from three phase voltage input within the IED. The pre-processing block calculates -V2
from the first three inputs into the pre-processing block by using the following formula:
( )
2
1
2
3
V VA a VB a VC
= × + × + ×
ANSIEQUATION00024 V1 EN-US
where:
VA, VB, VC are fundamental frequency phasors of three individual phase voltages.
To use this all three phase-to-ground voltages must be connected to three IED VT
inputs.
This phasor is used together with the phasor of the operating current, in order to determine the
direction to the fault (Forward/Reverse).To enable voltage polarizing the magnitude of polarizing
voltage must be bigger than a minimum level defined by setting
VpolMin.
Note that –V2 is used to determine the location of the fault. This ensures the required inversion of
the polarizing voltage within the function.
8.5.7.3 External polarizing for negative sequence function
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1MRK 502 066-UUS B Section 8
Current protection
499
Technical manual