Experimental and Analytical Studies on Electromagnetic Behaviors of the GdBCO Racetrack Coils in a Time-Varying Magnetic Field

Yoon Hyuck Choi,Seungyong Hahn,Hyun-Jin Shin,Dong-Hyung Kang,Haigun Lee Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3

<P>The electromagnetic responses of two GdBCO racetrack coils, one wound without turn-to-turn insulation (NI) and the other wound with Kapton tape (INS), were examined in a time-varying magnetic field generated by a permanent magnet mounted on a rotor, which was driven by a separate motor. The currents induced by the electromotive forces were measured with respect to the rotating speed, number of turns, and the distance (d) between the permanent magnet and the coil. In the case of the NI coil, delay of the induced current was observed in a time-varying magnetic field (5 rpm, d = 10 mm) due to anisotropy of the current path, suggesting that delay of the induced current will affect the electromagnetic induction by dB/dt. Consequently, the maximum induced current (0.35 A) of the NI coil was 8.2 times lower than that of the INS coil (2.88 A). Moreover, the induced currents in the INS coil increased with increasing rotating speed and number of turns, as well as with decreasing d, while those of the NI coil were barely affected due to the anisotropic current path. The experimental results showed good agreement with the simulated ones, which validates the proposed approaches involving an NI equivalent circuit model.</P>

A study on charging and electrical stability characteristics with no-insulation and metal insulation in form of racetrack type coils

Quach, Huu Luong,Kim, Ho Min The Korea Institute of Applied Superconductivity a 2020 한국초전도저온공학회논문지 Vol.22 No.3

This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.

Analytical and empirical studies on the characteristic resistances of no-insulation GdBCO racetrack pancake coil under various operating currents

김광록,최윤혁,D.G. Yang,D.H. Kang,J.H. Kim,김호민,이해근 한국물리학회 2015 Current Applied Physics Vol.15 No.1

This paper presents the effects of the Lorentz force on the electrical behaviors of the no-insulation (NI) GdBCO racetrack pancake (RP) coil without turn-to-turn insulation by performing charging/discharging and sudden-discharging tests. The simulation results of the 2-dimensional finite element method showed that the Lorentz forces were generated towards the center of the winding pack consisting of 60- turn GdBCO CCs, which could enhanced the turn-to-turn contact within the RP coil. The charging/discharging test results indicated that the characteristic resistance (Rc) of the NI RP coil decreased with increasing operating current, which was caused by an increase of the Lorentz force. Further, the results of the sudden-discharging tests exhibited that the Lorentz force was dissipated instantly during the sudden-discharge of the coil, since the operating current immediately decreased to zero. Overall, this study clearly demonstrated that the Lorentz force induced by the operating current exerts the electrical behaviors of an NI RP coil.

A study on electromagnetic and mechanical characteristics of the field coil in HTS motor

Kim, S.B.,Kadota, T.,Joo, J.H.,Sano, H.,Murase, S.,Lee, S.H.,Hong, J.P.,Kim, H.M.,Kwon, Y.K.,Jo, Y.S. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.20

High temperature superconducting (HTS) motors electromagnetically consist of a rotator wound with HTS wires and an armature with conventional copper wires like Litz wire. The HTS rotor windings, as field coils, consist of a straight part and an end-ring part. Because a major rotation torque is induced by an interaction between magnetic fields and current-carrying conductors in the straight part, most of mechanical stresses in the motor occur at the straight part. An end-ring is placed in the edge of the straight part and used to connect to each adjacent straight-part coils. The magnetic fields by coil currents concentrate on the end-ring part, therefore, it is expected that the critical current of the entire coil, straight and end-ring, can be determined by the magnitude of the field in the end-ring. This paper deals with the overall J<SUB>c</SUB> degradation in the end-ring part by self-field generated from the coil. In addition to electromagnetic analyses, we have performed a numerical analysis in order to evaluate mechanical stresses in the straight part of field coil by armature reaction on steady-state operation. The analytical results will be presented in this paper.

Stress analysis of HTS racetrack coils for 10 MW class superconducting wind power generator

Kwangmin Kim(김광민),Gyeong-Hun Kim(김경훈),Minwon Park(박민원),In-Keun Yu(유인근) 한국산업정보학회 2013 한국산업정보학회논문지 Vol.18 No.2

The authors designed a high temperature superconductor (HTS) racetrack coil for a 10 MW class superconducting synchronous wind turbine generator. The designed HTS racetrack coil was analyzed by an electromagnetic finite element method (FEM) to determine the magnetic field distribution, inductance, stress, etc. This paper describes the stress analysis and structure design result of the HTS racetrack coil for 10 MW class superconducting synchronous wind turbine generators, considering orthotropic material properties, a large magnetic field, and the resulting Lorentz force effect. Insulated HTS racetrack coils and no-insulation HTS racetrack coils were also considered. According to the results of the stress analysis, the no-insulation HTS racetrack coil results were better than the insulated HTS racetrack coil results.

10 MW 급 초전도 풍력발전기용 고온초전도 레이스트렉 코일의 응력 해석

김광민,김경훈,유인근,박민원 한국산업정보학회 2013 한국산업정보학회논문지 Vol.18 No.2

The authors designed a high temperature superconductor (HTS) racetrack coil for a 10 MW class superconducting synchronous wind turbine generator. The designed HTS racetrack coil was analyzed by an electromagnetic finite element method (FEM) to determine the magnetic field distribution, inductance, stress, etc. This paper describes the stress analysis and structure design result of the HTS racetrack coil for 10 MW class superconducting synchronous wind turbine generators, considering orthotropic material properties, a large magnetic field, and the resulting Lorentz force effect. Insulated HTS racetrack coils and no-insulation HTS racetrack coils were also considered. According to the results of the stress analysis, the no-insulation HTS racetrack coil results were better than the insulated HTS racetrack coil results.

Analysis on electrical and thermal characteristics of MI-SS racetrack coil under conduction cooling and external magnetic field

Yoon Seok Chae,Ji Hyung Kim,Huu Luong Quach,Sung Hoon Lee,Ho Min Kim 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4

This paper presents the analysis and experiment results on the electrical and thermal characteristics of metal insulation (MI) REBCO racetrack coil, which was wound with stainless steel (SS) tape between turn–to–turn layers, under rotating magnetic field and conduction cooling system. Although the field windings of superconducting rotating machine are designed to operate on a direct current, they may be subjected to external magnetic field due to the unsynchronized armature windings during electrical or mechanical load fluctuations. The field windings show the voltage and magnetic field fluctuations and the critical current reduction when they are exposed to an external magnetic field. Moreover, the cryogenic cooling conditions are also identified as the factors that affect the electrical and thermal characteristics of the HTS coil because the characteristic resistance changes according to the cryogenic cooling conditions. Therefore, it is necessary to investigate the effect of external magnetic field on the electrical and thermal characteristics of MI–SS racetrack coil for further development reliable HTS field windings of superconducting rotating machine. First, the major components of the experiment test (i.e., HTS racetrack coil construction, armature winding of 75 kW class induction motor, and conduction cooling system) were fabricated and assembled. Then, the MI racetrack coil was performed under liquid nitrogen bath and conduction cooling conditions to estimate the key parameters (i.e., critical current, time constant, and characteristic resistance) for the test coil in the steady state operation. Further, the test coil was charged to the target value under conduction cooling of 35 K then exposed to the rotating magnetic field, which was generated by three phrase armature windings of 75 kW class induction motor, to investigate the electrical and thermal characteristics during the transient state.

Analysis on electrical and thermal characteristics of MI-SS racetrack coil under conduction cooling and external magnetic field

Yoon Seok Chae,Ji Hyung Kim,Huu Luong Quach,Sung Hoon Lee,Ho Min Kim 한국초전도저온학회 2021 한국초전도저온공학회논문지 Vol.23 No.4

This paper presents the analysis and experiment results on the electrical and thermal characteristics of metal insulation (MI)REBCO racetrack coil, which was wound with stainless steel (SS) tape between turn–to–turn layers, under rotating magnetic fieldand conduction cooling system. Although the field windings of superconducting rotating machine are designed to operate on adirect current, they may be subjected to external magnetic field due to the unsynchronized armature windings during electrical ormechanical load fluctuations. The field windings show the voltage and magnetic field fluctuations and the critical current reductionwhen they are exposed to an external magnetic field. Moreover, the cryogenic cooling conditions are also identified as the factorsthat affect the electrical and thermal characteristics of the HTS coil because the characteristic resistance changes according to thecryogenic cooling conditions. Therefore, it is necessary to investigate the effect of external magnetic field on the electrical andthermal characteristics of MI–SS racetrack coil for further development reliable HTS field windings of superconducting rotatingmachine. First, the major components of the experiment test (i.e., HTS racetrack coil construction, armature winding of 75 kW classinduction motor, and conduction cooling system) were fabricated and assembled. Then, the MI racetrack coil was performed underliquid nitrogen bath and conduction cooling conditions to estimate the key parameters (i.e., critical current, time constant, andcharacteristic resistance) for the test coil in the steady state operation. Further, the test coil was charged to the target value underconduction cooling of 35 K then exposed to the rotating magnetic field, which was generated by three phrase armature windings of75 kW class induction motor, to investigate the electrical and thermal characteristics during the transient state.

Development and Testing of 2G High Temperature Superconducting (HTS) Field Coils for HTS Synchronous Machines

Muralidhar Bathula V. A. S.,Sharma D. K.,Choudhury U. K.,Rao V. V. 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.3

High temperature superconducting (HTS) synchronous machines are compact and light weight machines with higher torque to weight ratio, lower noise and better dynamic response for strategic and critical industrial applications. The development of HTS fi eld coil is one of the main technological challenges in realizing the HTS synchronous machines, as it involves the selection of HTS tape, winding technology, handling of the HTS tape while winding on a winding machine and testing of the developed HTS coil at desired cryogenic temperatures. With advancements in HTS tape technology, recent 2G HTS tapes are off ered with higher engineering current densities with respect to 1G HTS tapes even at higher magnetic fi elds. Hence, the replacement of 1G HTS fi eld coils of previously designed 200 kVA HTS synchronous machine with 2G HTS fi eld coils at the same operating cryo-temperature shows a potential to enhance its capacity to 350 kVA (more than 75% increase in machine output). In the present work the details of design, development and testing of a double pancake type 2G HTS fi eld coil are presented for capacity enhancement of earlier 1G based 200kVA HTS synchronous machine.

Effective 3-D FEM for large-scale high temperature superconducting racetrack coil

Xiangyu Huang,Zhen Huang,Xiaoyong Xu,Wan Li,Zhijian Jin 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.3

In various types of large-scale electrical applications, the number of coil turns in such machines is usually large. Electromagnetic simulation of large-scale superconducting coils (tens to hundreds of turns) is indispensable in the design process of superconducting electrical equipment. However, due to the large scale of the coil and the large aspect ratio of super-conducting material layer in HTS coated conductor, it is usually difficult or even unable to perform 3-D transient electromagnetic simulation. This paper introduces an effective 3-D electromagnetic simulation method for large-scale HTS coated conductor coil based on T-A formulation. The simulation and experimental results show that the 3-D model based on the T-A formulation using homogeneous strategy is more accurate than the traditional 2-D models. The memory usage is not sensitive to the number of turns and this model will be even more superior as the number of turns becomes larger.