Theoretical Considerations on Eddy Current Losses in Non-Magnetic and Magnetic Pipes for Power Transmission Systems

摘要

The conventional methods of calculating eddy current losses in cable sheaths are now to be reconsidered, due to the facts that high current cables, realized by large conductor and/or forced cooling systems, are increasingly used for power transmission, and also that aluminum sheaths are widely used for power cables. To utilize the forced cooling systems, such as 22 kV internally water cooled cable with current carrying capacity of 15000A, attention should be paid to eddy current losses in neighboring steel materials, such as water return pipe, reinforcing rods in the concrete tunnel etc. Eddy current losses are also concerned with not only protective steel pipes, occasionally used for conventional cables, but pressure retaining pipes for gas spacer cables and cryogenic cables. As the energy density of power transmission is increasing, the eddy current loss problems are becoming more and more important in various fields. However, conventional formulas can only solve limited cases. Therefore, the authors have deduced general formulas on eddy current losses in non-magnetic and magnetic pipes, which are derived from electromagnetic field theory. These formulas are given in the forms of precise and approximate solutions for both cases where conductors are placed inside and outside the pipe in any configuration. To verify these theoretical formulas, typical examples of comparison between measured and calculated losses are presented. One is shown in Fig. 9, which is an example of eddy current losses on non-magnetic pipe with outside conductors. Another is shown in Fig.