Boris A. Shoykhet

Status of the 1000 HP HTS motor development

Progress has been made in the development of high efficiency HTS motors with the aid of Department of Energy funding under the Superconductivity Partnership Initiative. This effort includes the fabrication and testing of synchronous motors with HTS field windings. The objectives of this development effort include saving half the losses of conventional motors in a package with half the volume. In Phase I of the present program, a 125 HP synchronous motor with an HTS field winding was designed and tested to levels in excess of 200 HP. This paper summarizes the status of a 1000 HP motor development which is part of a Phase II effort. The program elements to be reviewed include the overall design characteristics of the motor, the status of the field coils and refrigeration system, and a description of other components of the 1000 HP motor system. The 1000 HP motor fully represents the design issues to be addressed in the 5000 HP motor also to be developed in Phase II.

Design and testing of a 1000-hp high-temperature superconducting motor

A synchronous motor with a high-temperature superconducting field winding has been successfully constructed and tested. Designed to produce an output power of 1000 hp, this motor was operated successfully at this power rating and achieved an output power of 1600 hp during subsequent testing. This paper provides an overview of the design of the motor and discusses the results of a series of tests which were performed on the motor.

Quench in High-Temperature Superconducting Motor Field Coils: Experimental Results at 30 K

The results of quench tests on high-temperature superconducting (HTS) motor coils conduction-cooled to 30 K are presented. In previous tests, the same coils were cooled by direct immersion in liquid nitrogen. In spite of both a significantly lower temperature and a different cooling mechanism, the 30 K tests confirm the previous results which showed that the quench process is characterized by a current level, referred to as the quench current, above which the cooling system cannot maintain the winding temperature. Currents in excess of this value will produce an unstable growth in winding temperature in a process commonly referred to as a coil quench.

Quench in High-Temperature Superconducting Motor Field Coils: Computer Simulations and Comparison With Experiments

For high temperature superconducting (HTS) motor field coils two types of quench initiation are of practical importance. The first type will be referred to as current induced quench (CIQ). It typically occurs during coil or assembled rotor testing, when the current is increased in small increments until the quench is detected. The current at which the quench starts is referred to as the quench current Iq [1]-[7]. The objective of these experiments is to establish actual limits of operational conditions. The second type will be referred to as temperature induced quench (TIQ) and it is caused by failure or malfunctioning of the cooling system. The examples include vacuum deterioration, cryocooler failure etc. Numerous CIQ experiments [1]-[8], [10] have showed a certain pattern of quench event, including a well defined Iq, slow near-linear increase with respect to time of coil voltage and temperature with subsequent transition to fast non-linear voltage and temperature growth. TIQ experiments [10] showed the same behavior when coil cooling system was shut down while the current was maintained constant. The presented here work is a computational 2-D and 3-D Finite Element Analysis (FEA) study of CIQ and TIQ in HTS coils. The effects of magnetic field, non-homogeneity of tape properties, current sharing and amount of stabilizer are studied. It is shown that the formation and propagation of the normal zone is preceded by the process that we chose to call pre-quench instability. The pre-quench instability starts when the current exceeds Iq and demonstrates experimentally observed features mentioned above. It is shown that with an insufficient amount of stabilizer for second generation (2-G) HTS tapes the pre-quench instability may be practically undetectable. The comparison with some of the experiments [8], [10] is presented. We intensively used the concepts developed in articles [1]-[6]. Many (but not all) our conclusions are in agreement with [1]-[6].

Quench in High-Temperature Superconducting Motor Field Coils: Reduced-Temperature Modeling of HTS Tapes

The concept of reduced temperature for the characterization of the electrical properties of HTS tapes is presented. The formulation was developed based on experimental data from [1] and verified by experimental data from [2], [3]. Also, the experimental data from [4]-[6] indicate that the same formulation may be applicable to NbTi and Nb3 Sn LTS superconductors. In general, the electric field in a superconductor is a function of four parameters: temperature, perpendicular and parallel magnetic flux densities and current. In the proposed formulation, the electric field is determined from only two parameters; the current and a quantity which we have chosen to call the reduced temperature. The latter is defined as the difference between the actual temperature and the critical temperature as determined by the perpendicular and parallel components of the magnetic flux density. This formulation results in considerable simplification in the application of the well-known power law for the DC electric field in HTS tapes. First, the characteristic current and the power exponent can be expressed as functions of the reduced temperature only. Second, the power exponent reduces to a function of the critical current alone.

Quench in High-Temperature Superconducting Motor Field Coils: Experimental Results

The results of quench tests on high-temperature superconducting (HTS) motor coils conduction-cooled to 30 K are presented. In previous tests, the same coils were cooled by direct immersion in liquid nitrogen. In spite of both a significantly lower temperature and a different cooling mechanism, the 30 K tests confirm the previous results which showed that the quench process is characterized by a current level, referred to as the quench current, above which the cooling system cannot maintain the winding temperature. Currents in excess of this value will produce an unstable growth in winding temperature in a process commonly referred to as a coil quench.