Seyeon Lee

Design of a Single Phase 33 MVA HTS Transformer With OLTC

HTS transformers which have been developed until now had only fundamental structures. Among the auxiliary functions of conventional transformers, voltage regulating is the most important one. For the voltage regulation, conventional transformers are equipped with on load tap changers (OLTCs). In this paper, we investigate the possibility of the HTS transformer with OLTC. For the case study, we designed a single phase 33 MVA HTS transformer with OLTC. It is one of three individual HTS transformers which composes a 3 phase, 100 MVA transformer. It is expected to substitute for a 3 phase, 60 MVA conventional transformer in Korea. The parameters of an HTS transformer are varied due to the gap length between primary and secondary windings. The length was decided for the transformer to have the impedance of 12%. Its size was limited to the one of the conventional transformer. The characteristics of the HTS transformer were analysed in both case of having OLTC and not.

Analysis of Eddy Current Losses and Magnetization Losses in Toroidal Magnets for a 2.5 MJ HTS SMES

A SMES magnet can be operating in three different modes: charging, storing, and discharging. The eddy current losses and magnetization losses are generated during charging and discharging in the SMES system. The eddy current losses per cycle are generated mainly during discharging period because the discharging period is generally shorter that for charging. Magnetization losses per cycle are generated mainly during the charging. In this paper, we investigated a decrease in eddy current losses according to the shapes of conduction cooling plates. The cooling plate having small eddy current losses was designed by dividing and slitting. Also, the magnetization losses in the toroidal coil constructed with many pancake coils were analyzed using 3-D finite element method during the initial charging period and some discharging periods in an operating scenario for the 2.5 MJ SMES.

Stress Analysis for Toroid-Type HTS SMES Coil and Bobbin Structure Considering Large Parallel Magnetic Field

A 2.5 MJ HTS superconducting magnetic energy storage (SMES) system is under development to compensate the sag or instantaneous black out for a utility side. The toroidal-type structure is adapted to reduce the perpendicular magnetic field and the stray field at outside of SMES. A toroidal-type magnet shows a small perpendicular magnetic field. However, parallel magnetic field is much larger than perpendicular one. Therefore, Lorentz force of HTS tape can be so strong and the stress analysis should be carried out to verify that the maximum hoop stress and normal stress are in appropriate range. In addition, overall inward force of an HTS pancake winding in toroidal-type magnet is very strong and stress analysis for the bobbin and its supporting parts is important for a design a mechanically stable structure. This paper describes an analysis and design result for a toroidal-type HTS SMES magnet considering orthotropic material properties, large magnetic field and the resulting Lorentz force.

Design of the Cryogenic System for 100 MVA HTS Transformer

A 100 MVA, commercial class high temperature superconducting (HTS) transformer was designed. In this paper the cryogenic system to extract the heat generated at the winding due to the AC loss and the heat penetration through the wall and the current lead and keep the winding temperature under design temperature is presented. The operation temperature is set at 67 K to increase the critical current and reduce the amount of HTS tape usage and the volume. The HTS winding was concentrically arranged to reduce the AC loss. The system consists of main cryostat with the windings and secondary cryostat with cooler, cryopump and the heat exchanger inside. The liquid nitrogen is entering the main cryostat at 65 K and assumed to be leaving at 67 K. The winding temperature distribution is simulated with the anticipated heat load using Fluent. The effect of the liquid nitrogen flow rate, inlet location is investigated and discussed.

Design of HTS Modular Magnets for a 2.5 MJ Toroidal SMES: ReBCO vs. BSCCO

A 2.5 MJ HTS SMES is being developed as a national program in Korea. This paper presents design results of modular HTS magnets for the 2.5 MJ toroidal SMES. We considered a choice of BSCCO-2223 or ReBCO tapes as the conductors for the HTS magnets of the SMES. Operating temperature was decided to be 20 K which could be accomplished by conduction cooling with a couple of GM cryo-coolers. Key design factors may include minimization of total conductor requirement and low AC loss.

Electrical Properties Analysis and Test Result of Windings for a Fully Superconducting 10 HP Homopolar Motor

This paper describes the electrical analysis and performance test result of windings of a 10 HP homopolar fully superconducting synchronous motor. The homopolar motor has high temperature superconducting (HTS) armature and field coils. The stationary field coils make the cooling system simple and easy because there is no cryo-moving part. The design of the motor and the analysis of magnetization loss generated in the superconducting armature windings are performed by finite element method. The critical current test results of the 2G superconducting wire, the pancake coil for field winding and the race track coil for armature winding are reported.

Characteristics of a Continuous Disk Winding for Large Power HTS Transformer

Because of the shape of the HTS tapes, the layer winding is not good for high voltage power transformer. The double pancake winding which is one of disk windings is good for the insulation and limitation of voltage stress, but it makes high AC losses. So we have proposed a new winding method which is called continuous disk winding (CDW) for high voltage HTS transformers and has advantages from both layer and double pancake windings. In this paper, we calculated numerically and measured AC losses in the HTS continuous disk winding. 4 kinds of short samples with different numbers of stacked HTS tapes were made and their AC losses were measured. These data were used in the process of calculation, making the result more precisely. Other properties such as the critical current, inductance and capacitance were analysed numerically and tested also.

A Conceptual Design of a Conduction-Cooled Magnet for a Superconducting Property Measurement System

We started a new project to develop the conduction-cooled measurement system for superconducting power apparatus. The measurement system is used to acquire electrical and thermal properties on short HTS tape samples and the system is composed of specimen holder for mounting HTS tape and a magnet for applying magnetic fields externally. The magnet consists of two split racetrack windings and is designed to produce maximum 3 T of center field at 20 K. The temperature of specimen holder can be varied in range from 10 K to 77 K. The field homogeneity, which is calculated the maximum magnetic field divided by the center field, is required less than 0.01 within 10 cm axially and 10 mm radially from origin. We have worked on the conceptual designs of the conduction-cooled magnet for the superconducting characteristic measurement system. The measurement system will be fabricated in near future based on the design parameters presented in this paper.

Characteristics of Rotating Armature Type High Temperature Superconducting Generators With Dual Field Windings for the Wind Turbine

We proposed an HTS wind power generator that has armature windings in the rotor. Field windings in the stator make a slightly higher magnetic field than the field windings in the rotor if both windings have same size of armature windings and field coils. In addition, we split the field windings into two and installed one of the split ones inside the armature, i.e., the so-called dual field windings. This structure is mechanically complex because the armature windings rotate between two stationary field windings. However, the output voltage of the 10-MW generator is 12% higher than that of the rotating field with this structural modification. We set up six different types of field winding arrangement and analyze the field magnitudes and field distributions in the armature and field windings of each one. Finally, the output voltages are calculated by a finite-element method at full load.

Persistent Current Mode of a 1-T-Class HTS Pancake Coil for NMR/MRI Applications

We had proposed a winding method, the so-called “wind-and-flip,” which enables a persistent current-mode operation of a high-temperature superconducting (HTS) pancake coil. Two pancake coils had been fabricated using this method and tested in a liquid nitrogen bath with an external magnetic field. The result showed that the time stability was not good enough to use for magnetic resonance imaging or nuclear magnetic resonance when they were magnetized by field cooling at 77 K. In this paper, the test results of a stacked HTS pancake coil for a center magnetic field of 1 T are presented. The coils were cooled to 20 K by conduction cooling using a Gifford-McMahon cryocooler. We measured the time stability of the persistent current-mode operation at 20 K, which shows a strong possibility of a high-field HTS magnet using this method.