Alstom MiCOM P545 - 3.8.7 Mutual compensation

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-135
OP
i.e.:
Phase advanced vector Vp
=  Vp  [cos(s) + jsin(s) ] * [ sin(d) + jcos(d) ]
=  Vp  [-sin(s-d) + jcos(s-d) ]
Phase advanced vector pZr
=  pZr  [cos (e) + jsin (e) ] * [sin (d) + jcos (d) ]
=  pZr  [-sin(e-d) + jcos(e-d) ]
Therefore, from equation 1:
m = Vp ÷ (p * Zr) at f = 0
= Vp sin(s-d) / (pZr * sin(e-d))
Where:
d = Angle of fault current f
s = Angle of Vp
e = Angle of pZr
Therefore the relay evaluates m which is the fault location as a percentage of the fault
locator line impedance setting and then calculates the output fault location by multiplying this
by the line length setting. When calculated the fault location can be found in the fault record
under the VIEW RECORDS column in the Fault Location cells. Distance to fault is available
in kilometers, miles, impedance or percentage of line length.
3.8.7 Mutual compensation
Analysis of a
ground fault on one circuit of a parallel over-head line shows that a fault locator
positioned at one end of the faulty line will tend to over-reach while that at the other end will
tend to under-reach. In cases of long lines with high mutual inductance, mutual zero
sequence compensation can be used to improve the fault locator accuracy. The
compensation is achieved by taking an input to the relay from the residual circuit of the
current transformers in the parallel line.
The MiCOM P54x provides mutual compensation for both the fault locator function, AND the
distance protection zones.