Takashi Himeno

Test results of the 100 kWh SMES model coil – AC loss performance

Abstract In order to establish a technology needed for a small-scale 100 kWh SMES device, an SMES model coil was fabricated. Performance tests were carried out at the Japan Atomic Energy Research Institute (JAERI) in 1996. After that, the coil was installed in the Lawrence Livermore National Laboratory (LLNL) facility and tested in 1998, in collaboration between Japan and the United States. The AC losses measured at LLNL were in good agreement with those measured at JAERI. It was reconfirmed that the coupling loss of the coil could be expressed in two components: one with a short and another with a long coupling time constant. We found out from the Hall probe signals that the loop currents with long decay times were induced in the CIC conductor by varying magnetic field. These currents resulted in additional AC loss in the coil. To develop a concept of CIC with low AC loss, we made a sub-scale CIC conductor of strands coated with CuNi. We fabricated a small coil out of this conductor and measured the AC loss. The measured AC loss in this coil was about 1/6 of that in the SMES model coil conductor per strand volume. Thus, the CuNi coating of the strands was demonstrated to be effective to reduce the AC loss in the coil.

Test results of the SMES model coil—pulse performance

A model coil for superconducting magnetic energy storage (SMES model coil) has been developed. To establish the technology needed for a small-scale 100 kW h SMES device, a SMES model coil was fabricated and tested in 1996. The coil was successfully charged up to about 30 A and down to zero at the designed magnetic-field ramp rate for the SMES. Alternating current (AC) losses in the coil were measured by an enthalpy method. The results were analyzed and compared with the test results from a short sample. The measured hysteresis loss is in good agreement with that estimated from the short sample results. It was found that the coupling loss of the coil could be described as consisting of two components with different coupling time constants. One has a short time constant of about 220 ms, which is in agreement with the test result of a short conductor. The other has a long time constant of about 30 s, which was not expected from the test results for the short sample.

AC loss performance of the 100 kWh SMES model coil

AC loss tests of the SMES model coil for 100 kWh SMES pilot plant were carried out at Lawrence Livermore National Laboratory (LLNL) in 1998, in collaboration between Japan and the USA. The AC loss results at LLNL were in good agreement with those obtained at the Japan Atomic Energy Research Institute (JAERI) in 1996. The coupling loss in the coil could be described by two components with a short time constant (0.22s) and a long time constant (30s). The short time constant was in good agreement with that measured in a short sample. The signals of Hall probes, mounted on the surface of the coil, revealed that the induced loop currents in the conductor decayed with long time constants. At least two long time constants were observed: about 4s and 100s. The long time constant was also identified by the observation of voltage decay after the coil discharge. These loops result in the additional AC loss in the coil. Effect of lateral force in the cable on losses was studied as well. An improved conductor aiming to reduce the AC loss was designed, fabricated and wound in a small coil. The measured AC loss in the small coil made of the improved conductor was about 1/6 of the SMES model coil per strand volume.

Development of the 20kA Class HTS Current Lead for A SMES

HTS current leads using YBCO leads for a l00kWh SMES pilot plants were developed. Moreover, a HTS lead experimental device that had a rated capacity of 20kA class and 3kV was produced and current loading tests and voltage loading tests were carried out. As a result, it was confirmed that the HTS current lead using YBCO leads had sufficient performances for practical uses through the various tests.