IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 5, NO. 2, JUNE 1995 453

Superconducting Linear Synchronous Motor for Urban Transport System

Daltro G. Pinattit', Te6filo M. Souzaz, and Carlos Y. Shiguet tCentro de Eng,"h"'a de Materiais, Faculdade de Engenharia Quimica de Lorena - Lorena - SP, Brazil - 12600-000

Instituto de Fisica "Gleb Wataghd, UNICAMP - Campinas - SP, Brazil - 13081-970 SCDT - Cmtro de Desenvolvimento de Tecnologia e Recursos H m o s - S.J. Campos - SP, Brazil - 12242-800

Abstrud-It is presented the basic project of a superconducting linear synchronous motor (SLSM) for high capacity urban transport system (lo6 passengers/day/line) able to go up hill grade of 12%. The motor is composed of 26 poles installed below one wagon and sufficient for traction of six wagons of 330 passengers each. The pole coil is a segmented race-track type 23 cm long, 140 cm wide, and 11.2 cm high. The conductor is composed of 14 transposed NbTi wires 4 0.7 mm each, 5.04 mm x 1.20 mm cross-section and CulSC ratio of 1.35. The current leads are made of hgh-T, superconductor (melt textured growth YBa2Cu30,-r). These leads allow a pool cooling cryostat (2400 I of m e ) without an on-board refrigerator, and with one year holding time. The quench protection is made with cross-quench heater resistance placed within each coil. The limiting factor is the critical field of the NbTi and its substitution by Nb3Sn should reduce the cost by a factor of 40%. Final cost of the SLSM is expected to be in the US$ 600,000 range. Due to the low speed (100 kmh), the suspension is made on conventional bus type tyres.

I. INTRODUCTION

The urban aglomeration in underdeveloped countries has a tendency of high concentration of population in the center surrounded by medium and low concentration in the suburbs. Transportation by underground systems are too expensive for the economical level of these countries and bus system does not have the large transport capacity required for medium and big cities. One example are the metropolis of S b Paul0 (20 x lo6 inhabitants) and Rio de Janeiro (10 x lo6 inhabitants) in Brazil, where conventional subway system has reached up to now only 40 and 20 km, respectwely. This work shows an urban transport system with cost as low as bus system and capacity as large as subway systems. Moreover, the system allows progressive construction with superconducting linear synchronous motor (SLSM) in the central parts of the cities and conventional bus in the suburban areas.

11. BASIC PRINCIPLES OF SEMI-SUBTERRANEAN METRO WITH SLSM

Fig. 1 shows the typical vehicle and Table I presents its main data. The vehicle is a biarticulated type bus with one SLSM for a

Manuscript received October 18,1994.

TABE 1 cHARAcTE3usTC DATA OF THE S U M SYSTEM

1) Weigbt ofvehicle (t): 14 (enpty), 35 (loaded). 2) Passengdvehicle: 160 (seated); 330 (tdal); 6 vehiclesham. 3) Capacity @ash): 40,000 (6 pass/m2t 53,000 (8 pass/m'). 4) Workiughours: 20trainSm, 2OWday. 5 ) Dimensions(m):

-vehicle: l a @ 25.20; width 3.00; heigbt 3.65. -track (stator): tdal width 1.40, effedive width 1.30,

pkb 0.48. 6) Curvature radius: horizontal 150 m, vertical 12%. 7) Wheel diam&r(m): 1.15. 8) Acceleratiddeacceleratim ( d s ' ) : 1.12. 9) Velocity(k"): max 108, connnerCial35. 10) Power: mator 8.12 kW, Inverter 10 MVA 11) Track voltage (V): 10,OOO. 12) Track ament (A): 600. 13) Aluminum cable: electrical resi&ivity 2.8 lo4 R.m

14) Maximum fiwluency (Hz): 62.5 15)PhaseangleP= 110". 16) Efficiacy q = 0.75. 17) Power fador = 0.95.

cmss-sxtim area: 4 x lo4 m2.

18) c4xt: - Inverter (US$/kW): 25 - Candudor (US$/m3): 23,000 - Stator (US$/m): 177.10 - Energy (US$/kWh): 0.04 - SC -wet (US$ for Six Vehides): 600,000 - Vehicle (US$): 500,000 -Interestrate: 15%

composition of six vehicles. For a period of 2 minutes between compositions and 20 hourdday operation it reaches lo6 passengerddayhe. Since the SLSM can go up hill grade of 12%, the track is constructed just below the street avoiding large cost of land expropriation, deep tunnel excavation and deep station construction. The use of SLSM technology results in a considerable cost reduction in the civil construction. The space for the truck tyre allows installation of one or two axis per truck (4 or 8 tyrdtruck). The system is provided with side guide and four wheel steering. The superconducting coils are situated 1.30 m below the passenger cabin and there is ample space for installation of a magnet shielding for reduction of magnet field within the cabin (lower than 0.1 mT).

Table II shows an example of real cost for conventional metro in Bradia City (Brazilian capital) presently under mnstruction. That system is a partial semi-subterranean

1051-8223/95$04.00 0 1995 IEEE

Fig. 1 . Typical vehicle with SLSM (units in mm).

metro with medium capacity (270,000 passenger/day/line) and its modification study for SLSM system (total semi- subterranean - large capacity) is done.

The relatively low cost for the SLSM system of US$24.13 x 1 0 6 h should be compared with the conventional Brasilia Metro itself (US$ 17.50 x 1 0 6 h ) and the cost of deep tunnel Metro with large capacity system of s2Lo Paul0 and Rio de Janeiro Metro (US$130 x 1 0 6 h ) .

Table I11 gives the specification of the force parameters, cryostat dimensions, weights, and SLSM cost. The pitch of the motor and of the three-phase track (0.48 m) are determined by the maximum of critical current against the critical field of NbTi superconducting wire. Calculation of inverter, stator (track), mutual and self inductances, forces, as well as otimization of pitch, conductor, section length, and energy consumption was published elsewhere [l], [2]. SLSM is a powerful motor but recovery of energy results in the lowest consumFon of energy (0.11 kJ/passengerh) among transportation systems, even inferior to a walking (0.19) or a bicycle ride (0.12).

The operation of a SLSM system in a Metro system is facilitated by the use of two types of inverter installed in alternatedstations: power and speed inverter control the

TABE I1 COST OF CO"TI0NAL BRASLLA METRO AND MODIFICATION WITH SLSM -,

4OKM(1O6US%)

Civil oonstrudon: Road bed (rail* 5, pavement + stator ) Stations (29) Maintenance shop Semi-subanem trench Civil oonstrudion for fixed systems E x d v e project for civil culstrudul Semi-Total (A)

Equipm-: Fmed systems

7.b) Telecommunications 7.c) Energy: AC power

8) Mobile systems (vehicle) 9) Equipnentpartsandcmtral

cmverter

maintenance

*-Total (B) 10) Automatic tidceting

Total (A+B) 11) CO*

CONVENTIONAL SLSM SYSTEM

132.34* 132.343** 40.51 40.51 11.19 11.19

126.62 (11 km) 460.54(40km)

0.21 0.21

15.54 15.54 326.41 660.23

46.43 46.53 21.97 79.40 0.60 -

182.39 (80)

34.21 9.00

373.91

2 1.97 79.40 1.43

11.75 100.80 (168)

34.21 9.00

304.99

700.32 965.22 17.50 24.13

motion of the incoming and outcoming section; transference inverter energizes the short length of the SLSM (25.2 m) aiming the transference of the train to the next power and speed inverter.

Trains are independently controlled during the motion and the parking in the station. Interlocking of the two systems yields integrated controlling.

TABLE III SPECIFICATION OF THE SLSM

1) Forces on the vehicle 1.1) Acceleration/Braking- 35,000 x 1.12 39.20 kN 1.2) Ramp (12Yo): 35,000 x 9.8 x 0.12 41.20 kN 1.3) Aerodynamic drag 1.45 kN 1.4) Tyelpavement contact 2.45 kN

acceleration 45.10 kN 270.60 kN

T a l force without superposition of ramp and max.

Total force for six vehicles

2) Horizontal motor force (pair of poles)

h Mfs = average mutual indudance h e e n one coil and stator I 4 1 = rms stator current

sen p = sm llOo= amtrol angle cos 0 = power factor q = eledromectranical efficiency

= polar pitch ofthe magnet

If =totalmagnetcurrent

25.73 kN

0.48 m 1.03 pH 600 A

1.12 x 10'A 0.94 0.95 0.75

455

TABLE III (CONTJNUATION)

10.52 270.60 2.2) Theoretical number of pole pairs = -

25.73 Senice fador 1.24 F’raticalnumberofpolepairs- 1 0 . 5 2 ~ 1.24 13 2.3) Nominal p e r : 270.60 x 30 d s 8.12 MW 2.4) I n v e power 10.0 MVA 3) Cryostat dimensions (mm) 3.1) h g h t

SC magnet: 26 x 240 6,240 LHe tank (4.2 K) 6,644 Shield (77 K) 6,672 External tank (300 K) 6,740

sc magnet 1,400

Shield (77 K) 2,240

sc mapet 120 120 120

3.2) Width

LHetank (4.2 K) 2,204

External tank (300 K) 2,330 3.3) Height: Lateral Max(centra1) Medium

LHe tank (4.2 K) 124 349 237 Shield (77 K) 50 493 272 External tank (300 K) 720 925 823

3.4) Surfam: 4.2 K (33.68 m’); 77 K (38.62 m*); 300K (46.27 m2). 3.5) W k t W ocg)

At4.2K Wire 2,042 Mapetic shield 1,330 LHe tank 539

At 77 K Thermal shield 50 1 At 300 K Extemal tank 5,182

Total weight 9,594 3.6) Volumes (m3)

LHe 2.4 LN2 4.0

Superamdudor cable (US$180.00kg) 360,000 Cryostat + strudure (7,500 kg. USS14.00kg) 105,000 POW^ Supply (35 kW - US$1,2OO.OOkW) 42,000 Controls 43,000 contingency 50,000 Total 600,000

4) Magnetic fabrication cost (US$):

double the pitch of the magnet and the frequency of operation, yelding a reduction of the SLSM cost.

A three-dimensional semi-analytical computer program was developed for calculation of magnetic field [3]. Input data to the program are: magnet dimensions, coordinates of the point field calculation, number of blocks in the semi- cylindrical sector, SC cable dimensions, packing factor, number and increments of points to be calculated, current density or unit value for G/A. Prome of the field can be obtained for any direction. Criteria of calculation is the minimum volume of superconducting cable (minimum cost).

The self inductance of the magnet is the sum of the self inductance of each coil (L,) and the mutual inductance between first neighbors (MQ) resulting in Lt = NLi + 2(N - 1)Mi = 26 x 0.275 + 2 x 25 x 0.052 = 9.75 H. The contribution of others neighbors are neghgible. The total energy stored in the magnet is Q = 1/2 I$ = 112 (9.75) (2,200)2 = 23.60 UT. This is Suflticient to evaporate 9,200 of LHe and the protection system must dissipate most of this energy outside of the cryostat.

I A I

111. THE SUPERCONDUCTING MAGNET

The SLSM is composed of 26 coils (13 pairs) shown in Fig. 2. It is an epoxy-impregnated segmented race-track coil generating a field of 6.5 T in the center and with maximum field of 7.0 T in the end of the straight section. The specifications of the NbTi cable are: dunension - 5.04 mm x 1.20 mm, constitution - 14 wires of C+ 0.7 mm each transposed; SC filaments - 54 with C+ 62 km each W S C ratio - 1.35:l; twist pitch - 25 mm; transposition length - 50 mm; critical current at 7 T and 4.2 K (1 pV/cm criteria) - 3,500 A; maximum length 2,500m. Taking 63% of the critical current and 0.9 for packing factor results in a winding current density of 330 “m2 and an operating current of 2,198 A.

A low cost Nb3Sn cable based on internal diffusion method for low field (9 T) is under development, allowing to Fig. 2. Dimensions (in cm.) of the race-track coil.

? +=7

25 -16.86LT

17.7081

-19.544-

-23.00-

456

IV. CRYOSTAT V. CONCLWSION

The conductor is isolated with epoxy-impregnated Kapton tape 25 p thick with dielectric strength of 303 V / m supporting a electric tension of 7,575 V. Resistance of the magnet is F&(300 K)/RRR = 5.4 W80 = 0.0675 R. In order to have a pratical value of protection resistance lR, we use a cross-quench device to force the simultanmus quench of all the 26 coils. The terminal voltage will be only 2,200 V.

The relation between energy dissipated in the magnet (E,) and in the protection resistor (Ep) is given by E& = &/I$,), = (1.0/0.0675p = 219.5. This results in Ec = 107.5 kJ, sufficient to evaporate only 41.5 t' of N e .

The cryostat has a partml flat bottom, a semi-arc top dome for helium vessel, a 77 K heat shield, and a flat top for room temperature vessel bolted below the vehicle. Helium vessel is made on stainless steel with plates between each coil linking top and bottom plates (cellular structure). Heat shield and external vessel are made in aluminum alloy in order to reduce weight and shield AC field from the stator in the track. Mechanical support from the magnethelium cryostat to the vehicle structure is made by fiberglass tube in isostatic construction in order to accommodate thermal contraction and decrease thermal and mechanical fatigue effects.

Current leads are made with LN, refrigerated Cu down to the 77 K level (evaporation rate: 96 May) and melted textured growth YBaCuO pod (MTG//ab - Jc = 15 A/mm2) down to the He vessel [4], - The helium cryostat volume is 2,400 t' and static evaporation is 4 !/day with connected current leads (in magnet recharging condition). For high-TT, superconducting current leads, persistent mode operation reduces the evaporation rate only 10%. Even if dynarmc evaporation is an order of magnitude greater, LHe charge should be made in a monthly basis. High temperature superconductor current leads eliminates the need for refrigeration on-board for the low temperature superconductor magnet. Compressed gas recovery is provided on-board [5 ] . The LN, tank is installed in the passenger cabin.

Maglev technology is already developed, but pure superconductor propulsion (SLSM and others) without levitation has not been fuuy explored. Low speed urban transportation can take advantage of the SLSM capacity to go up hill in high grade (12% or more) and should develop semi-subterranean or elevated transportation system. Utilization of tyre and bus type technology can reduce the present cost of large capacity urban transport system by a factor of five.

NbTi superconducting magnet and cryostat technologies are well developed. The use of superconducting ceramic as current lead eliminates the need of on-board refrigeration and considerably decreases the consummon of LHe. The present work shows that there is considerable room to increase safety factor with respect to magnetic, mechanical, thermal, and electrical stability.

REFERENCES

[l] G.R. Slemon, R.A. Turton and P.E. Burke, "A linear synchronous motor for high-speed ground transport," IEEE Trans. Magn., vol. 10, no. 3, pp. 435-438, 1974.

[2] D. L. Atherton et al., "Superconductive magnetic levitation and linear synchronous motor propulsion for high speed guided ground transportation," Canadian Maglev Group - Ed. A. R. Eastham. CIGGT. Report 75-

[3] V. Santos Filho, "Calculation, design and fabrication of a race-track coil," MSc Thesis, no. 18/1994 CEMAR - Centro de Engenharia de Materiais, FAENQUIL - Lorena - SP, Brazil (In Portuguese).

[4] E. Grivon et al., "YBaCuO current lead for liquid helium temperature applications," IEEE Trans. Magn., vol. 27, no. 2, pp.1866-1869, March 1991.

[5] B. Gamble, D. Cope and E. Leung, "Design of a superconducting magnet system for Maglev applications," IEEE Trans. Appl. Supercond., vol. 3 , no. 1, pp. 434-437, March 1993.

5, p ~ . 49-85.