Toshinobu Ito

Development of MVA class HTS SMES system for bridging instantaneous voltage dips

A SMES system of MVA class for bridging instantaneous voltage dips has been developed using Bi-2212 wire. The Bi-2212 wire has high-performance conductive characteristics that do not deteriorate at a low temperature in high magnetic fields beyond 10 T. These characteristics enable a compact design of a SMES system of the Bi-2212 wire. In addition, coils of the Bi-2212 wire can be adequately insulated due to a high temperature margin. Therefore, the SMES system designed by using the coils has advantages to enhance dielectric strength and output power of the system. In our previous study, a SMES system consisting of 4 unit coils was constructed and the various properties were examined. Up to the present, the total 18 unit coils were stacked to make a coil system (outer diameter: 700 mm, height: 554 mm, stored energy: 984 kJ) and installed into a SMES system of 1 MVA for bridging instantaneous voltage dips. Also, the cooling system of the HTS SMES has been improved. The characteristics of the conduction cooled HTS coils of 1 MJ class were investigated in the operations of 1 MVA SMES system for bridging instantaneous voltage dips. Thermal reliability was verified during each operations of exciting, standby, bridging and current damping. Moreover, the repetitive bridging operations even worked out every 5 minutes. Advantages of the conduction cooled HTS coils for SMES were verified.

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.

Electrical circuit models among superconducting strands in real-scale CICCs

Stability margin of the cable-in-conduit conductor is greatly influenced by current transfer performance among strands. When we estimate the stability margin analytically, we must assume the electrical circuit model among strands, but it is difficult to know it for real-scale cables, because the cable has many parallel circuits with a lot of strands and twisted stages. The measurement of the frequency characteristics of impedance among strands shows that the circuit can be regarded as two-wire model. By this measurement we can judge whether the circuit behaves like a distributed constant circuit or a lumped element circuit within the intended frequency band. When the circuit is a lumped element circuit, we can also get the interval distance between each contact point and its resistance. This paper also shows that stable conductors are often represented with a lumped element circuit that has well-contacted points with a short interval.

Stability simulation of a cable-in-conduit conductor on a non-uniform mesh

A new stability simulation code of a cable-in-conduit conductor (CICC), POCHI, has been developed. In POCHI, a large amount of CPU time could be saved by applying an implicit time-dependent scheme and linearization technique for a fluid dynamic equation. This linearization also makes the scheme stable. However, the use of the uniform mesh makes the CPU time long for stability simulation of a long CICC. POCHI has therefore been improved to make the grids fined only on the necessary regions. As a result, more CPU time could be saved. The simulated and experimental results of stability for a small CICC were compared for verification of the improved code. The results were in good agreement, resulting in verification of the code.