Fig.1 shows the cross-sectional view of a basic electric circuit of the SECT system. As can be seen, one of the two cables connected with an AC power source of 50 Hz or 60 Hz is passed through the inside of a small diameter steel tube (SECT tube) and connected to the tube at the end opposite to the power source. The other cable is connected with the other end of the tube to form a complete circuit. When AC current is passed through the steel tube, it does not flow uniformly through the cross section of the tube but concentrates near the inner surface of the tube because of the skin effect. It is well known that the skin effect phenomenon of alternating current is very often encountered with in the high frequency domain. However, when a ferromagnetic material such as steel is used as a conductor, it exhibits the remarkable skin effect even at the commercial frequency because of the high permeability of steel. The skin depth is normally used as an index for the intensity of this effect. When comparison is made between copper and steel conductors in terms of the skin depth, it is found that the skin depth for steel is about 0.1 that of copper at the commercial frequency. At the frequency of 50 Hz, the skin depth is calculated to be in a range of 1 millimeter (1/25 inch) for normal steel. This indicates that practically all the current is confined to the limited wall portion 1 millimeter (1/25 inch) depth from the inner surface of the tube. The SECT circuit is essentially resistive and has a power factor of approx. 0.9 without compensation.