Z. XU ET AL.

Copyright © 2013 SciRes. ENG

5.431+j40.132

The model of two lines with mutual inductance is

sho wn in F i gure 9.

Figure 9. The model of two lines with mutual in ductance

The voltammetry characteristic can be written as fol-

lows,

（7）

So when we measure the zero sequence self imped-

ance of the line I, the zero sequence current of line II

which influences the zero sequence voltage of line I

should be taken into account. The traditional method

ignores the influence of line II, so there are theoretical

mistakes in (9) .

（8）

Then,

（9）

From （7）, we can get,

10101220

10 10 10

UUZI

ZII

−

= ≠

（10）

In fact, it indicates that when the current of line I

reaches 100 A and the current of line II reaches 47 A,

can’t be ignored. So the error of zero sequence

self impedance measured by traditional method is great.

In this measurement, the error has reached above 30%.

Measure the zero sequence voltages and zero sequence

currents of all transmission lines, then calculate (1) and

obtain zero sequence self impedance and zero sequence

mutual impedance. The live line measurement method

not only has high precision, but also is accurate and reli-

able. The measurement results of zero sequence parame-

ters are shown in table III, it shows that the average

measurement error of zero sequence mutual impedance is

about 5.5% and zero sequence self impedance is about

2%.

It shows that there are still certain difference between

theoretical values and measurement values. It is well

known that the computation formulate for zero sequence

parameters are derived from Carson formula. The tradi-

tional method needs the resistance of earth, the equiva-

lent depth of wires, the length of lines and the arrange-

ment of wires. But it is difficult to get the resistance of

earth and the equivalent depth of wires. So the theoreti-

cal values are only used as reference, they cannot be used

as accurate parameters.

In the case of disturbing, in order to obtain the accu-

rate parameters of zero sequence self impedance, the

zero sequence self impedance and the zero sequence

mutual impedance should be measured at the same time.

7. Conclusion

The field l ive l ine mea suri ng r esult s ha ve pr ove n tha t th e

live line measurement method is correct and the mea-

surement system can meet the requirement of measure-

ment. In addition, in order to eliminate the interference

of lines, using the live line measurement method to cal-

culate the zero sequence self impedance parameters and

the zero sequence mutual impedance parameters simul-

taneously can improve the accuracy of the measurement

results.

8. Acknowledgemen ts

This work was financially supported by the Ph.D. Pro-

grams Foundation of Ministry of Education of China

(20110141110032).

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