U3N
U2N
U1N
C1 C3
LP
Ip
IC2
IC3
N U1E
U2E
U3E
UNE
earth
IF
ZF=0
I1
I2
I3
GP
Figure The equivalent circuit resonant earthed neutral system with P-coil and a
single phase-to-earth fault
Une U31
1
2 3
U21
Ground
IC2+ IC3
ILp
IC2
IC3
IGp IP
Uen
IGp
IF
ILp
IC2+IC3
under
compensation
over
compensation
full compensation
a) b)
Figure Vector diagram with earth fault phase (fault impedance Ω)
b) Impact different tuning positions fault current IF
LP, P-coil (inductance and conductance)
C1, C2, Line-to-earth capacitances
ZF Impedance the faulty section
N Neutral point the transformer
U1E, U2E, U3E Phase voltages
UNE Zero sequence voltage
IC2, IC3 Capacitive currents the two healthy lines
IP Current through the P-coil when earth fault occurs
IGP Active component IP
ILP Reactive component IP
IF Current across the faulty section
The following assumptions are made for the derivatives:
0 The line-to-earth capacitances and conductances are symmetrical
0 All unbalances are allocated Line 1
0 For first observations, load current flowing
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