Figure 52: Distribution Of Currents During A C Phase To Earth Fault; Figure 53: Theoretical Case - No Resistance Present In Xl Or Xc - GE P24DM Technical Manual

Chapter 6 - Current Protection Functions
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Figure 52: Distribution of currents during a C phase to earth fault

The figure below shows vector diagrams for the previous system, assuming that it is fully compensated (for
example, coil reactance fully tuned to system capacitance), in addition to assuming a theoretical situation where
no resistance is present either in the earthing coil or in the feeder cables.
I
H3
I
L
I
H2
I
H1
I
A1
N
C
a) Capacitive and inductive currents
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Figure 53: Theoretical case - no resistance present in XL or XC

With reference to the associated vector diagram, it can be seen that the the C-phase to earth fault causes the
voltages on the healthy phases to rise by a factor of 3. The A phase charging currents (Ia1, Ia2 and Ia3), are then
shown to be leading the resultant A phase voltage by 90° and likewise for the B phase charging currents with
respect to the resultant Vb.
126
I
L
jX
L
I = I + I
L F
A
I
B1
B
I
A1
I
B1
I
R1
-jX
C1
I
H1
I
A2
I
B2
I
R2
-jX
I
H 2
I
A3
I
B3
I = I
C3 F
I
R3
-jX
I
F
I
I
H3
+ I + I
H1
H1 H2 H3
3V
0
I = I
R1 H1
I
b1
I
a1
V = -3V
res o
b) Unfaulted line
C2
C3
+ I
H2
I
L
-I
H1
-I
H2
I I
R3 R3
V = -3V
res o
c) Faulted line
P24xM
= I + I
F H3
= I - I - I
L H1 H2
P24xM-TM-EN-2.1