38
6
F
2
S
0
8
3
4
Setting of earth fault compensation factor (zero sequence compensation)
In order to correctly measure the positive-sequence impedance to the fault point, the current input
to the earth fault measuring elements is compensated by the residual current (3I0) of the protected
line in the case of a single circuit line and by residual current (3I0) of the protected line and
residual current (3I0’) of the parallel line in the case of a double circuit line.
Generally, the following equation is used to compensate the zero-sequence voltage drop in the
case of phase “a”.
Va = (Ia
−
I0)Z1 + I0
×
Z0 + Iom
×
Zom (1)
where,
Va: Phase “a” voltage
Ia: Phase “a” current
I0: Zero-sequence current of the protected line
I0m: Zero-sequence current of the parallel line
Z1: Positive-sequence impedance (Z1 = R1 + jX1)
Z0: Zero-sequence impedance (Z0 = R0 + jX0)
Z0m: Zero-sequence mutual impedance (Zom = Rom + jXom)
Equation (1) can be written as follows:
Va = (R1 + jX1)Ia +
{
(R0
−
R1) + j(X0
−
X1)
}
I0 + (Rom + jXom)Iom
=
R1(Ia +
R0
−
R1
R1
I0 +
Rom
R1
Iom) + jX1(Ia +
X0
−
X1
X1
I0 +
Xom
X1
Iom)
In the GRZ100, the voltage is compensated independently for resistance and reactance
components as shown in equation (2) in stead of general equation (1).
VaR + jVaX =
{
R1( IaR +
Krs
100
−
1
3
×
3I0R +
Krm
100
3
×
3IomR )
−
X1( IaX +
Kxs
100
−
1
3
×
3I0X +
Kxm
100
3
×
3IomX )
}
+ j
{
R1( IaX +
Krs
100
−
1
3
×
3I0X +
Krm
100
3
×
3IomX )
+ X1( IaR +
Kxs
100
−
1
3
×
3I0R +
Kxm
100
3
×
3IomR )
}
(2)
where,
Kxs: compensation factor (Kxs = X0/X1
×
100)
Krs: compensation factor (Krs = R0/R1
×
100)
Kxm: compensation factor (Kxm = Xom/X1
×
100)
Krm: compensation factor (Krm = Rom/R1
×
100)
X: imaginary part of the measured impedance
R: real part of the measured impedance
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Summary of Contents for GRZ100-211B
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