7.5.2.2 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 can be
set to use voltage polarizing or dual polarizing.
Voltage polarizing
When voltage polarizing is selected, 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.
The negative sequence voltage is pre-processed by a discrete fourier filter. Thus, the
phasor of the fundamental frequency component of the negative sequence voltage is
derived. 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.
Dual polarizing
When dual polarizing is selected, the function uses the vectorial sum of the voltage
based and current based polarizing in accordance with the following formula:
( )
2 2
TotPol VPol IPol Pol Pol Pol Pol Pol
V V V V Z I V R jX I= + = - + × = - + + ×
ANSIEQUATION2315 V1 EN (Equation 90)
1MRK505222-UUS C Section 7
Current protection
423
Technical reference manual
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