THE PERFORMANCE OF REDUCED MAGNETIC-FIELD POWER-LINES THEORY AND MEASUREMENTS ON AN OPERATING LINE

Because of the recent concerns that power frequency magnetic fields mi ght affect biological systems, power engineers have been trying to fin d transmission line geometries that will reduce fields. One of the red uced field geometries that has been in existence for many years is the so-called double circuit, low reactance line. Such a line if balanced (i.e. positive sequence currents) can have fields that are a factor o f three lower than a single circuit line on the right-of-way Off the r ight-of-way much greater reduction is achieved because the field atten uates much faster. However, it has been found through analytical studi es that magnetic fields are very sensitive to small deviations from po sitive sequence currents due to load unbalance; therefore the field re duction is not as great as predicted for a balanced line, especially o ff the right-of-way. This paper reports the results of a measurement a nd a theoretical program to study the magnetic field performance of a double circuit 230-kV line with only one circuit energized and with bo th circuits paralleled in a low reactance configuration. As expected, the measurements show that the reduced field line is more sensitive to deviations from balanced currents.