Areva MiCOM P441, Technical Manual

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Application Notes P44x/EN AP/E33
MiCOM P441/P442 & P444 Page 25/220
(5) VA = Z1 [IA + kZ0 IR]
(6) Z1 = VA/(IA + kZ0 IR)
Particular case
Resistive fault
(7) VA = Z1 [IA + kZ0 IR] + Rdef. Idef (Rdef = Rloop)
To determine the distance, Z1 term is extracted.
(8) Z1 = (VA – Rdef. Idef)/(IA + kZ0 IR)
with
Rdef: fault resistance (loop)
Idef: current crossing the fault resistance
Open line:
Ifault = IR = IA
(9) VA = Z1 IA (1 + kZ0) + Rfault IA
(10) Z1 = (VA/IA – Rfault)/(1 + kZ0)
The impedance detected will be:
Z = Z1 (1 + kZ0) + Rfault
That is the form used for the result of Z measured with injector providing U, I,
ϕ
Separate compensation for each zone (KZ1, KZ2, KZ3/4 and KZp) allows more accurate
earth fault reach control for elements which are set to overreach the protected line, such that
they cover other circuits which may have different zero sequence to positive sequence
impedance ratios (Example: underground cable & overhead line in the protected line).
2.7.6 Resistive Reach Calculation - Phase Fault Elements
In MiCOM S1 all resistances are set per loop
The P441, P442 and P444 relays have quadrilateral distance elements, thus the resistive
reach (RPh) is set independently of the impedance reach along the protected line/cable.
RPh defines the maximum amount of fault resistance additional to the line impedance for
which a distance zone will trip, regardless of the location of the fault within the zone. Thus,
the right hand and left hand resistive reach constraints of each zone are displaced by +RPh
and -RPh either side of the characteristic impedance of the line, respectively. RPh is
generally set on a per zone basis, using R1Ph, R2Ph and RpPh. Note that zones 3 and 4
share the resistive reach R3Ph-R4Ph.
When the relay is set in primary impedance terms, RPh must be set to cover the maximum
expected phase-to-phase fault resistance. In general, RPh must be set greater than the
maximum fault arc resistance for a phase-phase fault, calculated as follows:
R
a
= (28710 x L) / I
f
1.4
RPh
≥
R
a
Where:
I
f
= Minimum expected phase-phase fault current (A);
L = Maximum phase conductor separation (m);
R
a
= Arc resistance, calculated from the van Warrington formula (
Ω
).