ABB Relion 670 Series RES670, Техническое руководство

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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.
8.3.7.2 Internal polarizing facility of the function
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
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 .
1MRK 511 365-UUS A
Section 8
Current protection
Phasor measurement unit RES670 2.1 ANSI 221
Technical manual