ABB Relion REG670, Техническое руководство

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( )
2
1
2 1 2 3
3
I IL a IL a IL
= × + × + ×
EQUATION2266 V2 EN
(Equation 68)
where:
IL1, IL2 and IL3 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 protection to compare it with the
set operation current value of the four steps (
I1> , I2> , I3> or I4> ). 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 STx (x=1 - 4) for this step and a common
START signal.
8.5.7.2 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 function uses the
voltage polarizing method.
NS4PTOC uses the negative sequence voltage -U2 as polarizing quantity U3P. This
voltage is calculated from three phase voltage input within the IED. The pre-
processing block calculates -U2 from the first three inputs into the pre-processing
block by using the following formula:
( )
2
2
1
1 2 3
3
UPol U
UL a UL a UL
= - = -
× + × + ×
EQUATION2267 V2 EN
where:
UL1, UL2 and UL3 are fundamental frequency phasors of three individual phase voltages.
To use this all three phase-to-earth 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
Section 8
1MRK502052-UEN B
Current protection
382
Technical manual