ABB Relion 670 series, Technical Reference Manual

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directional zero sequence current can be used. Current reversal and weak-end infeed
functionality are available.
7.5.2 Principle of operation
Four step negative sequence overcurrent protection NS4PTOC (4612) function has the
following three “Analog Inputs” on its function block in the configuration tool:
1. I3P, input used for “Operating Quantity”.
2. V3P, input used for “Voltage Polarizing Quantity”.
3. I3PPOL, input used for “ Polarizing Quantity”.
These inputs are connected from the corresponding pre-processing function blocks in
the Configuration Tool within PCM600.
7.5.2.1 Operating quantity within the function
Four step negative sequence overcurrent protection NS4PTOC (46I2) function always
uses negative sequence current (I2) for its operating quantity. The negative sequence
current is calculated from three-phase current input within the IED. The pre-processing
block calculates I2 from the first three inputs into the pre-processing block by using the
following formula:
( )
2
1
2
3
I IA a IB a IC
= × + × + ×
ANSIEQUATION2266 V1 EN
(Equation 89)
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 negative sequence current is pre-processed by a discrete Fourier filter. Thus, the
phasor of the fundamental frequency component of the negative sequence current is
derived. 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.
Section 7
1MRK505222-UUS C
Current protection
422
Technical reference manual