GE MiCOM P40 Agile Technical Manual page 194

P44x/EN AP/Hb6
(AP) 5-42
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, RpPh and RqPh. 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, e.g. calculated as follows:
R
a
RPh
Where:
I =
f
L =
R =
a
Typical figures for R
phase fault current.
Conductor
spacing (m)
2
5
8
Table 2: Typical arc resistances calculated using the Van Warrington formula
The maximum phase fault resistive reach must be limited to avoid load encroachment trips.
Therefore, R3Ph and other phase fault resistive reach settings must be set to avoid the
heaviest allowable loading on the feeder. An example is shown in Figure 20 below, where
the worst case loading has been determined as point "Z", calculated from:
Impedance magnitude,
Leading phase angle,
Where:
kV =
MVA =
PF =
1.4
= (28710 x L) / I
f
≥
R
a
Minimum expected phase-phase fault current (A);
Maximum phase conductor spacing (m);
Arc resistance, calculated from the van Warrington formula (Ω).
are given in Table 2 below, for different values of minimum expected
a
Typical system I
voltage (kV)
3.6 Ω
33
9.1 Ω
110
14.5 Ω
220
Z
∠Z
Rated line voltage (kV);
Maximum loading, taking the short term overloading during out ages of
parallel circuits into account (MVA);
Worst case lagging power factor.
= 1kA I = 5kA
f f
0.4 Ω
1.0 Ω
1.5 Ω
2
= kV / MVA
–1
= cos (PF)
Application Notes
MiCOM P40 Agile P442, P444
I = 10kA
f
0.2 Ω
0.4 Ω
0.6 Ω