S.K. Baik

Joint resistances between two parallel high Tc superconducting tapes

Eight different types of joining between two parallel high Tc superconducting (HTS) tapes were prepared and current-voltage (I-V) characteristic curves were investigated at 77 K, liquid nitrogen temperature. Contact resistances of joint parts with 25 mm in length were estimated from I-V curves. Lowest contact resistance among eight samples having different types of joining was 0.497 /spl mu//spl Omega/. The best joining method is to do crossly joining with HTS tapes on two parallel HTS tapes after filling solder paste into their gap. In this case, lowest joint resistance was 0.15 /spl mu//spl Omega/ at 77 K and 0.05 /spl mu//spl Omega/ at 28 K. Joule heat of a joint sample generated at 30 K and at 100 A was calculated 0.492 mW. Also, in I-V curve of samples crossly joined with HTS tapes, it was found that joint resistance does not depend on variation of magnetic fields (0/spl sim/7000 G) at 77 K. From consideration of Joule heat generation, such joining method is available for fabricating the field winding of superconducting rotating machine.

Development of a 100 hp synchronous motor with HTS field coils

A 3-phase, 100 hp, 4 pole, 1800 rpm superconducting synchronous motor built and tested in Korea Electrotechnology Research Institute(KERI). This machine consists of HTS rotor and air-core stator. The HTS field windings are composed of the double-pancake coils wound with AMSCs stainless steel-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. The open circuit, no-load, and short circuit characteristic were obtained. Also, load tests in motor mode driven by inverter and generator mode connected to resister load bank were conducted. This paper will present design, construction, and experimental test results of the 100 hp HTS machine.

Status of HTS Motor Development for Industrial Applications at KERI & DOOSAN

This work is development of HTS motor at DOOSAN heavy industry and Korea Electrotechnology Research Institute in Korea, and is sponsored by DAPAS program which is supported by Korean government. The final aim of the project is realization of HTS motor in the field of industry such as large driving pumps, fans and compressors for utility and industrial environments. In the first phase (2001-2004), 100 hp HTS motor was developed in order to implement the preliminary technology for the large applicable HTS motor. All of the performance characteristics are well met to the designed ones. In second phase (2004-2007), 1 MW HTS motor is developed for the purpose to fully represent the design and manufacturing issues for the larger capacity machine. The machine is 2 pole and 3600 rpm, and all of the components are completely manufactured. This machine is now under assembly. This paper summarizes the status of 1 MW HTS motor development, such as design, construction, and experimental test results.

Investigation of Thermal Quench Characteristic in the HTS Bi-2223 Racetrack Coil

The thermal stability and quench propagations are one of the most fundamental issues for the High Temperature Superconducting (HTS) coil. Superconductivity is confined within the phase surface bounded by magnetic field, temperature, and current. Of these three parameters, the temperature is neither completely controllable, nor predictable, because the energy stored in the magnet, can easily be converted into heat up setting the thermal equilibrium within the winding. Therefore, in HTS coil operation, the temperature stability or more generally the thermal behavior of the conductor is the most important. In this paper, a HTS double racetrack pancake coil was prepared to examine the thermal stability, quench propagation and minimum quench energy (MQE). HTS coil was wound using the AMSC Bi-2223. The experimental results are discussed in this paper.

Effect of Synchronous Reactance and Power Factor on HTS Synchronous Machine Design and Performance

Synchronous reactance is an important parameter of synchronous rotating machine because it affects on the machine output capacity, voltage variation and steady-state stability. The superconducting synchronous rotating machine has very small synchronous reactance about 1/5 of the conventional synchronous machine. This reason comes from the fact that the superconducting rotating machine is air-cored structure. In this paper, it is estimated how much this synchronous reactance has influences on many design parameters of superconducting synchronous machine such as machine volume and weight, efficiency, voltage variation and so on. In the case of a synchronous motor, the power factor can be adjusted according to the excitation voltage. This paper also deals with the effects of power factor on the design parameters and the performance of a HTS (High-temperature Superconducting) synchronous motor. This kind of analysis was used to design 1 MW class HTS motor

Design considerations for 1 MW class HTS synchronous motor

A 1 MW class superconducting synchronous motor is designed considering several conditions such as superconducting wire length, machine efficiency and size. As the machine is larger and larger, the superconducting machine shows the advantages more and more over the conventional machines. Although the advantages at 1 MW rating are not so great, the design approach to get an appropriate result would be very helpful for larger superconducting synchronous machine design. Major design concerns are focused on reducing expensive Bi-2223 HTS (High Temperature Superconducting) wire which is used for superconducting field coil carrying the rating current around 30 K (-243/spl deg/C) while the machine efficiency is higher than conventional motors or generators with the same rating. Furthermore, some iron-cored structure is considered to reduce the HTS wire requirement without bad effect on machine performances such as sinusoidal armature voltage waveform, synchronous reactance and so on.

Soldered double pancake winding of high temperature superconducting tape

To make a superconducting coil by winding a High Temperature Superconductor (HTS) tape conductor on a bobbin, the double pancake winding technique is widely used to reduce number of splicing contacts between conductor pieces. However, this makes some Ic (critical current) degradation on kink points of the conductors, which is unavoidable. Soldered double pancake can be an alternative way to overcome the Ic degradation. This paper describes and compares the two ways of winding; usual double pancake, and soldered double pancake. Characteristics of the windings are measured and compared. The soldered double pancake winding has resistance on the contact points, but the estimated Joule heating on the contacts is much smaller than heat leak of cryostats.

A 30 kVA superconducting generator development and basic tests

A 30 kVA superconducting generator has been designed, developed and successfully tested by the Korea Electrotechnology Research Institute (KERI). The design is based on a 2-dimensional electromagnetic field analysis of cylindrical coordinates. The field winding of rotor has been wound with superconducting wire of NbTi alloy and tested after assembly with other rotor components. The stator has air-gap type armature windings, which produce higher terminal voltage, and a more sinusoidal voltage waveform than conventional iron cored machines. Steady-state open and short-circuit tests and lamp load tests have also been conducted. The results of these tests are given in this paper and compared with design quantities. Moreover, the cooling scheme and characteristics of the test system are included.

Design and Manufacturing of a Conduction-Cooled Sample Holder for a Superconducting Property Measurement System

We had developed four years ago a superconducting property measurement system (SPMS) that can be used to acquire electrical and thermal properties of high-temperature superconductor (HTS) tape samples. The SPMS was composed of the sample holder for mounting an HTS tape and 3 T HTS magnet, both cooled individually by conduction using a cryocooler. The maximum dimension of the HTS tape sample that could be loaded on the sample holder was 15 mm in width and 250 mm in length. The conduction-cooled sample holder was again fabricated to increase the maximum test current up to 800 A. Maximum transport current was 763 A in magnetic field intensity 3 T. The measuring temperature range was 15-50 K.

Loss analysis of a 1 MW class HTS synchronous motor

The HTS (High-Temperature Superconducting) synchronous motor has advantages over the conventional synchronous motor such as smaller size and higher efficiency. Higher efficiency is due to smaller loss than the conventional motor, so it is important to do loss analysis in order to develop a machine with higher efficiency. This paper deals with machine losses those are dissipated in each part of a HTS synchronous motor. These losses are analyzed theoretically and compared with loss data obtained from experimental results of a 1 MW class HTS synchronous motor. Each machine loss is measured based on IEEE 115 standard and the results are analyzed and considered based on the manufacturing of the test machine.