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In ZG, this function provides the compensation factors for all elements and these factors
are defined with settings. For example, for Z1G, the settings [Z1G-Krs], [Z1G-Kxs], [Z1G-Krm],
[Z1G-Kxm] are provided. Where, “s” refers to the protected line; the resistance “r”; the
reactance “x” reflect its property and “m” refers to a mutual circuit line for parallel line
applications.
Table 2.10-3 ZG compensation factors in lines
Settings for Protected line
Settings for Parallel line
Measuring the positive-sequence impedance to the fault point is necessary. Therefore, for
a single circuit line, the current input to the earth fault-measuring element is compensated by
the residual current (3I
0
) of the protected line.
On the other hand, for a double circuit line, the current input is compensated by the
residual current (3I
0
) of the protected line and residual current (3I
0
’) of the adjacent line.
Generally, the following equation is used to compensate the zero-sequence voltage drop,
in this example for the case of phase “a”.
where,
Va: Phase “a” voltage
Ia: Phase “a” current
I
0
: Zero-sequence current of the protected line
I
0m
: Zero-sequence current of the adjacent line
Z
1
: Positive-sequence impedance (Z
1
= R
1
+ jX
1
)
Z
0
: Zero-sequence impedance (Z
0
= R
0
+ jX
0
)
Z
om
: Zero-sequence mutual impedance (Z
om
= R
om
+ jX
om
)
Equation (2.10-32) can be presented as follows:
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