Hiroshi HATAChief Researcher | Hiroki KAMIJOSenior Researcher | Hiroyuki FUJIMOTOChief Researcher | ||

Traction control G., Vehicle control technology Div. | Superconducting materials G., Materials technology Div. |

**1. Introduction**

High Tc superconducting wires such as Bi2223 have made great progress in recent years. As a result, a prototype superconducting transformer rated around 1 MVA was manufactured. Its merits are lightweight and high efficiency. We have carried out a rough design study of a superconducting traction transformer to evaluate its merit. This work was carried out in conjunction with Kyushu University .

**2. Premise for a design study**

We assumed the specification of the transformer as Table 1 in consideration of the current design for Shinkansen type rolling stock.

Input power | 3 MVA |

Voltage (prim./second.) | 25 kV / 1 kV |

Current (prim./second.) | 120 A / 1 kA~3 |

Frequency | 60 Hz |

The weight of conventional transformer according to Table 1 is estimated to be 2800kg. We used the specification of the high Tc superconducting wire that presently has the best performance. When AC current flows in a superconducting wire, an AC loss is generated, which must be compensated for by a refrigerator. We show an image of superconducting transformer in Fig.1

We assumed four cases for the design study. When compared with the present wire, the Ic and AC loss are:

Case1: | Ic the same, AC loss the same |

Case2: | Ic twice, AC loss the same |

Case3: | Ic the same, AC loss 1/10 |

Case4: | Ic twice, AC loss 1/10 |

Ic means the critical current. "Ic twice" and "AC loss 1/10" assume the progress of superconducting wire technology in the near future. For all these four cases, we calculated five cases of 1-turn voltage.

**3. Results**

In all cases, we first determined the dimensions of windings and core. Then we carried out magnetic field distribution analysis for the windings and calculated the AC loss, which is a function of the magnetic field applied to the windings. Finally we calculated the weight of transformer including a refrigerator. The results are shown in Fig.2. As for the cases 1 and 2, the weight is around 2600 kg which is slightly lighter than that of conventional transformer. In the case 4, the minimum weight is around 1800 kg, 30% lighter.

We calculated the improvement of efficiency in Case3. Result is shown in Table2.

Case(Type) | Conventional | Superconducting |

AC loss | ---- | 299 W |

Other loss | 131 kW | 170 W |

Refrigerator input | ---- | 12 kW |

Efficiency | 95.8% | 99.4% |