Configuration of Standard 4-pole SC Coils

Transcription

1 Study of the Configurations of the Superconducting Magnet to Reduce Magnetic Field Leakage Hiroshi YOSHIOKA, Eiji WATANABE, Takashi SASAKAWA, Ken WATANABE, Nobuo TERAUCHI, and Erimitsu SUZUKI Maglev Systems Development Department, Railway Technical Research Institute Hikari-cho, Kokubunji-shi, Tokyo, JAPAN Abstract The inherently stable electrodynamic support system (EDS) for Maglev using superconducting magnets realizes levitation, guidance, and propulsion forces by making use of the powerful reciprocal interaction between on-board superconducting coils (SC coils) and ground coils. It is one of the most important tasks to reduce the leakage of magnetic flux generated by the SC coils, which would reduce the amount of necessary magnetic shielding material. This report deals with the configuration of the superconducting magnet (SCM) in a Maglev system to reduce the weight of magnetic shielding material. This SCM configuration reduces the weight of magnetic shielding by using SC coils of shorter length span at the ends of the SCM. This report examines SCM configurations designed from the viewpoint of magnetic shielding and magnetic flux density distribution in the cabin. 1. Introduction The electrodynamic support system (EDS) using superconducting magnets realizes levitation, guidance and propulsion forces by making use of the powerful reciprocal interaction between onboard superconducting coils (SC coils) and ground coils. It is one of the most important tasks to reduce the leakage magnetic flux generated by the SC coils, which would reduce the amount of necessary magnetic shielding material. In the present system, the Maglev train has an articulated bogie arrangement. Each bogie has two SCMs, on the left and right sides. Each SCM contains four SC coils arranged in alternating magnetic poles. The magnetic field around the bogie becomes comparatively high, especially at the front and rear ends of the bogie. This is because the magnetic flux generated by the end SC coils diverges at the front and rear ends of the SCMs, while the flux generated by the intermediate SC coils are cancelled out. An SCM configuration using SC coils of shorter length span at the front and rear ends can modify the distribution of the magnetic field. This report examines the SCM configuration designed from the viewpoint of magnetic shielding and magnetic flux density distribution in the cabin. 2. Configuration of SC coils and magnetic shielding 2.1 Standard 4-pole configuration First, we describe the standard 4-pole configuration and magnetic shielding Configuration of SC coils The standard 4-pole configuration is shown in Figure 1. The bogie is 5.4 m long and has two SCMs, one on the left side and the other on the right side. Each SCM contains four race-trackshaped SC coils arranged in alternating magnetic poles. The pitch of the SC coils is 1.35 m and the magnetomotive force is 700 ka. Configuration of Standard 4-pole SC Coils

2 2.1.2 Configuration of magnetic shielding The configurations of the Maglev vehicle and the magnetic shielding are shown in Figures 2 and 3. Magnetic shielding is installed in the shaded regions shown in the figures. Two cabins are connected by a gangway, which has a smaller width and higher floor level than the passenger rooms in order to maintain distance from the SCM, which is the origin of the magnetic flux. The result is a lower magnetic field in the gangway, requiring less shielding. Figures 2 and 3 show that the shielding is installed only at the regions around the bogie at the articulated section between two cabins. Configuration of Magnetic Shielding (Top View) Configuration of Magnetic Shielding (Cross Section)

3 2.2 Modified 4-pole and 5-pole configurations Second, we describe the modified configurations that use SC coils of shorter length span at the front and rear ends (the modified 4-pole and 5-pole configurations with shorter end coils). The modified 4-pole configuration has two standard coils between the shorter end coils as shown in Figure 4, while the 5-pole configuration has three standard coils as shown in Figure 5. Configuration of Modified 4-pole SC Coils Configuration of Modified 5-pole SC Coils 3. Weight of magnetic shielding and flux distribution in the cabin We study the configuration of magnetic shielding using the FEM method under the condition that the flux density is less than 20 Gauss in the gangway and 10 Gauss in the passenger room. The calculated values and measured values have been compared in a previous study (Sasakawa, 1993). We consider the saturated flux density (Bs) of the shielding to be 1.5 T and the density of shielding material to be 7.8 x 10 3 kg/m 3 in the calculation of the weight of magnetic shielding. 3.1 Weight of magnetic shielding The results of estimation of the weight of magnetic shielding for the modified 4-pole and 5-pole configurations are shown in Figure 6. These values are the sums of the weight of the shielding for the cabins and the gangway per bogie. Figure 6 shows that the greater reduction of the coil length span (shorter end coil) results in a greater reduction of the weight of shielding. The ratio of reduction of the weight of shielding to that of the coil length span is larger with the modified 5-pole configuration than with the 4-pole configuration.

4 Weight of Magnetic Shielding The weight distributions are shown in Figure 7 for the cases of the modified 4-pole and 5-pole configurations with a length span reduction of x = 0.24 m in Figures 4 and 5 and the case of the standard 4-pole configuration with a length span reduction of x = 0 m. The weight of shielding is about 690 kg per bogie in the case of the modified 4-pole configuration and about 410 kg in the case of the 5-pole configuration, which is 85 % and 50 %, respectively, of the weight of the magnetic shielding in the standard 4-pole configuration. Comparison of Weight of Magnetic Shielding 3.2 Distribution of flux in the passenger room To study the distribution of flux density, we built a mock-up model of the cabin for the standard 4-pole configuration and took measurements. We also calculated that the flux density distribution in the modified 5-pole configuration, and compared the two cases. Figure 8 shows the positions of measurement and calculation, which are horizontal and vertical planar regions 0.1 m above the floor

5 and 0.1 m in front of the end wall of the passenger room, respectively. shielding used are about the same as the weights shown in Figure 7. The weights of magnetic Calculation Area of Distribution of Flux Density Distribution of flux density at the floor of the end of the passenger room Figure 9 shows the result of measurement for the distribution of flux density on the horizontal plane 0.1 m above the floor of the end of the mock-up model in the standard 4-pole configuration. Figure 10 shows the results for the modified 5-pole configuration with the length span reduction of x = 0.33 m in Figure 5. Distribution of Flux Density of Standard Configuration on Cabin Floor (Experimental Results of Mock-up Model)

6 Distribution of Flux Density of Modified 5-pole Configuration on Cabin Floor (Experimental Results of FEM) In Figures 9 and 10, the horizontal axis indicates the position along the direction of travel (longitudinal direction) with zero being the position of the wall of the deck of the cabin, and the vertical axis indicates the position along the lateral direction from the center of the cabin. The flux density is 10 Gauss or less and is comparatively high around the vehicle entrance/exit at the sides of the deck and the wall separating the deck from the passenger room, which are the regions nearest to the SCM Distribution of flux density on the end wall and side walls at the end of the passenger room In the same way, we measured and calculated the distribution of flux density on the vertical plane 0.1 m in front of the end wall. The results are shown in Figures 11 and 12. The horizontal axis indicates the position along the lateral direction, and the vertical axis indicates the position along the vertical direction. The origin is the center of the cabin on the floor.

7 Distribution of Flux Density of Standard Configuration on End Wall (Experimental Results of Mock-up Model) Distribution of Flux Density of Modified 5-pole Configuration on End Wall (Experimental Results of FEM)

8 The farther the position from the floor, the lower the flux density, because the distance from the SCM is larger. There is no shielding at the lateral center region of the end wall because there is a gangway, and the flux density is comparatively high. Nevertheless, this flux density is 10 Gauss or less, which satisfies the conditions of the design of the magnetic shielding. 4. Conclusions We studied the configurations with modified end SC coils to improve the performance of magnetic shielding. The results indicate that the weight of magnetic shielding can be reduced when the configuration is modified from the standard 4-pole type to the modified 4-pole or modified 5- pole type, in which case the weight can be reduced to 50 % of that of the standard 4-pole configuration. Even when taking into account that the SCM becomes heavier because the structure becomes more complicated, the total weight of the car body can be reduced by 10 %. In addition, the properties of electrodynamic forces of these modified configurations are nearly the same as those of the standard 4-pole configuration. References 1) Takashi SASAKAWA, Static Magnetic Field Calculation using Scalar Potential. IEE of Japan (in Japanese), SA-93-1, RM-93-39, pp 1-5, August ) Nobuo TERAUCHI and Takashi SASAKAWA, Study of the Configuration of the Superconducting Magnet to Reduce Magnetic Field Leakage, RTRI Report (in Japanese), Vol. 14, No. 11, November ) Takashi SASAKAWA, Toshiaki MURAI, and Shunsuke FUJIWARA, Configuration of Superconducting Magnet for the Reduction of Leakage Magnetic Field and Improvement of Electromagnetic Force and Characteristics. Trans. IEE of Japan (in Japanese), pp , Vol. 120-D, No. 4, 2000.