This paper investigates the feasibility of magnetic fields reduction by optimization of phase relationships in a multi-circuit underground power cable system, carrying unbalanced loads. A novel algorithm was developed for fast calculation of the multi-circuit power cable system-generated magnetic field. The unbalanced load was modeled by random selection of phase current values. A computer code was written to calculate the statistical distribution of the magnetic field above the cables on the ground level. The program calculates the maximum magnetic field for different phase relationships and selects the optimum phase relationship. Several multi-circuit power cable systems used by electric utilities have been analyzed. The results show that the optimization of phase relationships effectively reduces the magnetic field for power cable systems with both single and multi-point grounded sheaths in spite of the load unbalance.

The feasibility of magnetic field reduction by phase relationship optimization in cable systems

A statistical method for predicting the annual cumulative probability distribution for the magnetic field of a set of power transmission lines is presented. This is necessary because of both random and more predictable variations of current on the lines. Also described is a simple method for calculating the currents induced on and magnetic fields of a series impedance loaded loop which is inductively coupled to the power lines. A program (MAGFLD 2.0) has been written to incorporate these methods and has been validated theoretically and experimentally by comparison to other programs and long term measured transmission line data respectively. >

Development and validation of software for predicting ELF magnetic fields near power lines

In this paper the authors compute the magnetic fields generated by a lot of typical power line configurations and compare these values with the results given both by analytical models and by measurements. The computations have been made by means of a flexible calculation code developed by the authors. This code overcomes some simplifying assumptions introduced in previous analytical studies. In fact, it is able to account the effective line route of the power line under analysis in a three-dimensional space. There are no limits on number and position both of energized conductors and of test points. >

Magnetic fields generated by power lines

Many issues related to electromagnetic analysis of power lines have been raised. These include some related to the operation of power lines, and others related to effects of the power-line electromagnetic environment. Concern about the latter has been responsible for a renewed interest by the media. An overview of these issues is given. When appropriate, the topics are placed in the context of methods commonly used by those trained in the electromagnetics of antennas and propagation. >

Power-transmission electromagnetics

Characteristics of the magnetic field under hybrid ac/dc high voltage transmission lines

Power engineers have been trying to find transmission line geometries that will reduce fields. One of the reduced field geometries is the double circuit, low reactance line. The results of a measurement and a theoretical program to study the magnetic field performance of such a double circuit 230 kV line with only one circuit energized and with both circuits paralleled in a low reactance configuration are presented. The measurements show that the reduced field line is more sensitive to deviations from balanced currents. >

D.C. James

Papers

The performance of reduced magnetic field power lines: theory and measurements on an operating line