P54x/EN OP/La4 Operation
(OP) 5-134
MiCOM P543, P544, P545 & P546
OP
3.8.5 Obtaining the vectors
Different sets of vectors are chosen depending on the type of fault identified by the phase
selection algorithm. The calculation using equation 1 is applied for either a phase to ground
fault or a phase to phase fault.
therefore for an A phase to ground fault:
pZr=a(Zline/THETA line) + n (Zresidual/THETA residual) ...(equation 2)
and Vp=VA
and for a A phase to B phase fault:
pZr=a(Zline/THETA line) - b (Zresidual / THETA residual) ...(equation 3)
and Vp = VA - VB
The calculation for a ground fault (equation 4) is modified when mutual compensation is
used:
pZr=a(Zline/THETA line
) +n (residual/THETA residual)+
m(mutual/THETA mutual) ...(equation 4)
3.8.6 Solving the equation for the fault location
As the
sine wave of f passes through zero, the instantaneous values of the sine waves Vp
and p can be used to solve equation (1) for the fault location m. (The term fRf being zero).
This is determined by shifting the calculated vectors of Vp and pZr by the angle (90° - angle
of fault current) and then dividing the real component of Vp by the real component of pZr.
(See Figure 85).
I
f = 0
Vp
I
pZr
I
pZr
Vp
P0125ENa
Figure 85 Fault locator selection of fault current zero
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