2. Basic Technology Development
A ground coil system was introduced, making much of reliability on the Yamanashi Test Line on the basis of superconducting magnet availability at the time of construction. However, the Kunitachi Institute basic technology development division is currently working on a substantially simplified cost-effective ground coil and a compliant highly vibration-resistant superconducting magnet. Research into further enhancement of on-board power supply is also underway.
(1) Relationship between Vibration of the Superconducting Coil and Mechanical Heating
One of the tasks to be tackled in the development of superconducting magnets when adopting simplified ground coils is heating of the superconducting coils during running. The relationship between vibration of the superconducting coils and the resultant heating was therefore examined. In particular, the relationship between yawing vibration of the superconducting coils (which becomes more pronounced when simplified ground coils are adopted) and heat generation was investigated by mechanical oscillation tests independent of electromagnetic influence. A simulated external basin with an incorporated superconducting coil was put into a mechanical oscillation testing device, and the heating value was measured based on helium evaporation when agitated laterally by external hydraulic pressure (Fig. 6). Comparison of the results with heat generation under torsional deformation (the cause of heating in the conventional superconducting coil) showed that heat generation from yawing vibration is significantly smaller than that of torsional vibration at equivalent vibration speeds (Fig. 7). The verification that heat generation by rigid body vibration such as yawing is very small suggests possible reductions in heating of the superconducting magnet compliant with the simplified ground coil during a run.
(2) Development of a two-window PLG Coil
Due to the enormous number of levitation coils installed on Superconducting Magnetically Levitated Transportation System, cost reduction, workability improvement and high reliability are required. As a measure to reduce construction costs by reducing the quantity of coil, a two-window combined propulsion, levitation and guidance (PLG) system coil with high withstand voltage (33 kV specification) was developed , which simultaneously serves these three functions (Fig. 8).
A conceptual design of the basic structures such as coil shape was first made, based on the basic specifications of the PLG coil. A prototype of a coil-connecting portion was then built with emphasis on higher reliability through size reduction and the omission of screws (Fig. 9). In addition, endurance tests were performed, including long-term outdoor conduction tests and long-term vibration tests of the coil-connecting portion. The results showed the new design to be safe for use as a ground coil.
Based on the above results, a prototype of the two-windows PLG coil with high withstand voltage was built, in which the height of the upper and lower unit coil was changed. A variety of verification tests showed that the coil had sufficient initial insulating strength for use as a PLG coil.
Plans are currently underway to verify the basic performance of the PLG coil through temporary use on the Yamanashi Test Line. At the same time its durability will be evaluated by performing long-term outdoor conduction and cyclic loading tests.
(3) Improved Inductive Power Collection Device
The inductive power collection device, an on-board power supply for superconducting magnetically-levitated transportation systems, can generate new electromagnetic forces between itself and the ground coil. Utilization of this device as a magnetic damping generator to improve riding comfort is being examined. Proposals were made for an improved inductive power collection system with greater generated force, which is now under development.
In this system, a magnetic field with a pitch equal to that of the superconducting magnet is generated. This is done by arranging inductive power collection coils (Fig. 10) and this system can generate approximately four times the vertical force of the conventional system. This system raises expectations of real improvements in riding comfort (Fig. 11). By changing the upper coil position, approximately 1.7 times the power collected by the conventional system can also be expected.
This system requires a new PWM converter that can generate current to generate a magnetic field with a pitch equal to that of the superconducting magnet. A new converter was therefore developed and its basic performance was verified.
The following plans are underway for fiscal 2003: the inductive power collection coil developed will be combined with the superconducting magnet and converter in the Kunitachi Institute for stationary tests to verify its overall performance. On-board running tests will then be performed on the Yamanashi Test Line.