Abstract and subjects
In a three-phase tri-axial cable, the magnetic interaction between the phases makes the loss measurement by an electromagnetic method very complex. We developed the theoretical background showing that three-phase AC loss measurements by the electromagnetic method are, in principle, possible. We then implemented this theory in practical measurements on a 3 m long, tri-axial cable fabricated from RABiTS (rolling-assisted biaxially textured substrate) coated conductor. Initially, the proposed measurement technique was implemented in the simpler cases when the three cable phases are 180 degrees out of phase, i.e. (0 degrees, 180 degrees, 360 degrees) or (0 degrees, 360 degrees, 180 degrees) rather than (0 degrees, 120 degrees, 240 degrees) as in a traditional three-phase system. For these cases, the currents in the phases are either in phase (360 degrees phase difference) or anti-phase (180 degrees phase difference). These are essentially single-phase measurements with only one transport current used as the supply for all three phases. This simplification allowed us to use both the established and the proposed techniques to measure the total losses of the cable for these cases. An excellent agreement between the two measurement methods confirmed the validation of our proposed measurement technique. The proposed measurement method was then employed to measure the total AC losses in a cable when it operates in the true three-phase mode. We believe that these data represent the first electromagnetic three-phase AC loss measurements.