Single Phase High Temperature Superconducting Research Articles

Application of Enhanced Optimal-Detection of Time–Frequency Domain Reflectometry on HTS Cable With High-Resolution

Time–frequency domain reflectometry (TFDR) has been used for sensing various types of cables including high temperature superconducting (HTS) cables. Recently, the optimal-detection of time–frequency domain reflectometry (OD-TFDR) has been proposed and has better detection and localization performance than conventional TFDR. Additionally, OD-TFDR has provided a threshold that can distinguish detected signals from Gaussian noise. However, OD-TFDR does not provide a criterion for classifying the detected signals into fault signals and artifacts. Furthermore, the diagnosis result of OD-TFDR is not intuitive because an additional tool is needed to locate each fault. Thus, this paper proposes a new diagnosis algorithm that can provides a criterion for distinguishing between artifacts and faults by considering the propagation direction of the incident signal in the join time–frequency domain while preserving the detection and localization performance of OD-TFDR. Through a template matching process of generalized time–frequency cross-correlation (GTFCC), the core algorithm of OD-TFDR, a modified–generalized time–frequency cross-correlation (M–GTFCC) function is derived. Next, a modified–time–frequency cross-correlation (M–TFCC) function is derived by slicing the M–GTFCC function considering the propagation direction of signal. Finally, M–TFCC function is proposed as a new intuitive diagnosis result with artifact-free and high-resolution. The performance of the proposed algorithm is tested via experimental setup for a real-world single phase HTS cable with an emulated local quench by heating element, and the efficacy of the proposed algorithm is verified based on three performances: fault detection, locating accuracy, and resolution.

Experimental Evaluation of Dielectric Losses of PPLP for Single Phase HTS Cable at Subcooled LN2 Temperatures

For the operation of high-temperature superconducting (HTS) power cables in liquid nitrogen (LN2 ) at high voltage levels, there is a need for reliable and cost-effective insulating materials. This article investigates the dielectric losses in poly-propylene laminated paper (PPLP- Sumitomo) which is used as a cold dielectric for HTS cables. To calculate the dielectric losses, an experimental setup was developed to measure the relative permittivity of PPLP at different temperatures from 65 to 300 K at various frequencies. Using an in-house developed experimental setup, the dielectric loss for different layers of PPLP, at various temperatures and operating frequencies was estimated to evaluate one of the criteria of cold dielectric material and the same was compared with the data at room temperature. The temperature was reduced to 65 K using a vacuum pump-assisted sub-cooling system. The effective relative permittivity increases marginally for subcooled LN2 impregnated PPLP, however there is reduction in tan delta loss which in turn reduces the dielectric loss and is useful for high voltage HTS based AC cables. This paper provides a comparative study on PPLP performance variation with respect to operating temperature and frequency.

Impact of the radius of double pancake windings on the electromagnetic behavior of high temperature superconducting transformer

PurposeIt has constantly been important to investigate the distribution of magnetic fields in high temperature superconducting (HTS) transformers because the high magnetic field applied to the HTS tapes reduces the critical current and increases the ac losses. The purpose of this study is investigation of the impact of the radius of double pancake windings on the electromagnetic behavior of HTS transformer. In this paper, by changing the radius of the windings in a step-by-step manner in two modes, the electromagnetic behaviors in double pancakes (DPs) of a single-phase HTS transformer have been investigated.Design/methodology/approachIn this paper a 15.4 kVA single-phase HTS transformer has been designed and simulated using the finite element method, using COMSOL multiphysics software. The effect of changing the radius of the low-voltage (LV) and high-voltage (HV) windings on the electromagnetic parameters such as distribution of circulating currents and magnetic field in the LV DP windings has been investigated.FindingsAccording to the results, by increasing the radius of the LV winding, the electromagnetic behavior of the highest and lowest DPs becomes highly undesirable, while in other DPs, it becomes desirable. The same thing happens by increasing the radius of the LV and HV windings, but with much less intensity. Therefore, according to Ce, the most optimal case is when the two windings (HV and LV) are close to each other and to the core, and if the radius needs to be increased, it is better to increase the radius of both windings.Originality/valueFor the first time, the impact of the radius of DP windings on the electromagnetic behavior of HTS transformer has been investigated.

A Study on a Single-Phase HTS Transformer with a Cylindrical Central Iron Core

During the past decade, a number of high temperature superconducting (HTS) transformer prototypes have been designed, and the majority of them are full-core transformers and air-core transformers. However, in this study, we proposed a new type of HTS transformer, where the iron core is different in that the limbs and connecting yokes are absent. To investigate the performance of this type of HTS transformer, we design and fabricate a single-phase HTS partial core transformer prototype using the secondary generation (2G) HTS GdBCO wires. The iron core is at room temperature, and the windings are immersed in liquid Nitrogen. The structures of primary and secondary windings are three layers connected in series and nine double pancakes connected in parallel, respectively. Fundamental characteristics are obtained by standard short-circuit, no-load and load tests in liquid Nitrogen temperature of 77 K. In addition, an equivalent circuit of the HTS transformer is proposed to analyze the characteristic of the transformer. The calculated values based on the equivalent circuit are consistent with that of experiment. The detailed results about the design of the HTS partial-core transformer, the experiment, and the equivalent circuit are presented and discussed in this study.

Current distribution among layers of single phase HTS cable conductor

High temperature superconducting (HTS) power cable shows high application prospect in modern power transmission, as it is superior over conventional transmission lines in high engineering current density and environmental friendliness. Its configuration is generally composed of several HTS layers designed with the principle of uniform current distribution, but there are few experimental results to verify the distribution. In this paper, a HTS cable model was designed based on the principle of uniform current, and the current distributions among layers in an HTS cable model were measured by Rogowski coils. The results provide an important basis for design of multi-layer HTS cable.

Conceptual Design of an HTS large power transformer with continuously transposed coated conductors

This paper shows results of a design work of a program that is to develop a large power single phase high temperature superconducting (HTS) transformer. The program forms a part of a national project in Korea. A target of the design work is an HTS power transformer with rated voltages of 154 kV/22.9 kV and material for windings is supposed to be coated conductor. The design results presents in this paper will include: 1)HTS winding structures for high voltage in liquid nitrogen, 2)design result of continuously transposed coated conductor (CTCC), 3)conceptual design of high voltage bushings, 4)cooling system. A feasibility study will succeed to this design work for construction of a prototype HTS power transformer with capacity/voltage of 33 MVA/154 kV.

Characteristic Test of a 1 MVA Single Phase HTS Transformer With Pancake Windings

A 1 MVA single phase high temperature superconducting (HTS) transformer was fabricated and a part of experimental test for characteristics of the transformer was performed. The rated voltages of primary and secondary of the HTS transformer are 22.9 kV and 6.6 kV respectively. BSCCO-2223 wire was used for HTS windings whose shapes are double pancake arranged reciprocally. Single HTS wire for primary windings and 4 HTS wires for secondary windings were used considering the rated current of the transformer. Four HTS wires in secondary windings were transposed at the connection between double pancakes 3 times. The electrical insulation and transport current test were performed at 77 K using liquid nitrogen. The rest of the test for the characteristics of the transformer is in progress.

Cryogenic Design of Termination Cryostat for HTS Power Cable

A high temperature superconducting (HTS) power cable system cooled by forced-circulation subcooled liquid nitrogen is under construction in Korea. In the system, the termination cryostat designed for normal capacity of 22.9 kV, 1.26 kA is located at each end. In order to cool the cryostat effectively, we conducted several numerical analyses. It was found that major design factors were position of inlet and outlet for the liquid nitrogen as well as mass flow rate of the liquid nitrogen in the cryostat. It was also found based on the calculation of temperature distributions in the cryostat that the mass flow rate of liquid nitrogen is needed at least 0.2 kg/s. The cryostat was designed to endure the mechanical stress induced by thermal shrinkage from room temperature to liquid nitrogen temperature. The cryostat is being installed in the 30 m length, prototype single phase HTS cable system.

The effect of flux diverters on AC losses of a 10 kVA high temperature superconducting demonstrator transformer

In this paper the design, construction and characterization of a 50 Hz single phase high temperature superconducting (HTS) transformer is presented. The transformer is designed to deliver 10 kVA at 77.4 K and 20 kVA at 65 K. The transformer is made of two windings positioned at the middle limb of a three-limb iron core. The secondary winding is made of nine double pancake superconducting coils, using silver sheathed BPSCCO-2223 multifilamentary tapes with nominal critical current of 20 A (at 77.4 K and self field). The primary winding is made of copper to reduce the cost of HTS material. Utilizing a superinsulated nonmetallic doughnut shaped cryostat with low background heat leak, the AC losses in the superconducting winding have been measured by calorimetric method. Two powdered iron flux diverters have been used inside the cryostat at both ends of the superconducting winding in order to reduce the radial component of leakage flux density in the HTS tapes. The use of these flux diverters is shown to be very effective in reducing the AC losses by 40% at the nominal current.

High temperature superconducting demonstrator transformer: design considerations and first test results

The paper highlights main features of a 10 kVA single-phase high temperature superconducting (HTS) demonstrator transformer built recently at the University of Southampton. One winding is made of BPSCCO-2223 tape with bulk critical current density of 22A/mm/sup 2/ at 77 K. Flux diverters have been used to reduce the radial component of leakage flux density in the HTS tape. Initial test results are shown with particular emphasis on measurements of ac losses.