Hee-Suk Ryoo

Performance Test of 100 m HTS Power Cable System

In order to meet the needs of economical and stable power supply and high current density cable with compact size, several countries carry out researches on high temperature superconducting (HTS) cables. Korea Electric Power Corporation (KEPCO) established the HTS cable test center and installed 22.9 kV, 1250 A, 50 MVA, 100 m class HTS cable system to investigate the performances and application possibility in real power grids. The HTS cable system went through seven cool down and warm-up cycles and also many kinds of performance tests for 3 years. Rated voltage-current tests, over voltage tests, and measurements of heat loss and AC loss with various currents have been examined. Moreover, DC critical current tests were performed for checking conductor degradation before warming up or after cooling down. Through the performance tests of the HTS cable system, the overall efficiency and loss factors are estimated and compared with conventional power cables in this paper. We conclude the present status of HTS cable system and application possibility in the real power grid.

The Results of Installation and Preliminary Test of 22.9 kV, 50 MVA, 100 m Class HTS Power Cable System at KEPCO

As high temperature superconducting (HTS) power cables have some merits over conventional cables, several demonstration projects on the HTS cable system are presently under way around the world. Korea Electric Power Corporation (KEPCO) also initiated an HTS cable project in 2002 with the Korean governments support. A three phase 100 m HTS cable system with a capacity of 50 MVA has been installed at Gochang test yard, located in Chonnbuk province, Korea. The HTS cable system is composed of a 100 m-long cable, two terminations and a cooling system. The rated current is 1,250 Arms and the rated voltage is 22.9 kV considering compatibility with the conventional power distribution system in Korea. Main purposes of this project are to verify the performance of an HTS cable system and to evaluate the potential of the HTS cable system from the viewpoint of power utilities. The real grid application of the HTS cable system requires the demonstration of system reliability, accumulated operation experiences, and it has to meet the practical needs of the utilities. In such a meaning, this project provides various challenges for KEPCO, and the feedback will be delivered to cable manufacturers. This user initiative test will facilitate the introduction of HTS cable systems into a real grid network. The installation process of the HTS cable system and some results of the preliminary test were presented in this paper.

EXPERIMENTAL STUDIES ON CRYOGENIC SYSTEM FOR 22.9 KV HTS CABLE SYTEM

In terms of high transmission capacity with lower voltage, a high temperature superconducting (HTS) cable system is a very attractive challenge for utilities. However, the concomitant cryogenic system for the HTS cable system is one of the tantalizing problems in the operation. The reliability and maintainability of cryogenic system are the key issues to apply it to the real electric power grid. Korea Electric Power Corporation (KEPCO) is making an attempt to verify the applicability of the HTS cable system to improve the efficiency of electric power industry. Since May 2006, a 22.9-kV, 50-MVA, 3-phase, 100-m class HTS cable system with an open cooling system has been operated at the KEPCO Gochang test yard. Concurrently, another HTS cable verification test with the same electrical specification and an hybrid cooling system has been carried out by LS Cable (LSC) Ltd in close proximity to the KEPCOs HTS cable system within Gochang test yard. KEPCO conducts the operation of the open cooling system, and is ...

THE RESULTS OF COOLING TEST ON HTS POWER CABLE OF KEPCO

Due to the inherent characteristics of the superconductivity that allows large power transmission capability, much research on high-temperature superconducting (HTS) power cables has been carried out world-wide. KEPCO (Korea Electric Power Corporation) had installed a three-phase, 100-m class, HTS cable system at Gochang power test center of KEPCO that handles 22.9 kV, 1250 A, 50 MVA. The HTS cable system of KEPCO consists of two terminations, the HTS power cable, and cooling system. Sub-cooled liquid nitrogen is used for the HTS power cable coolant, providing an inlet temperature to the cable during operations from 66 K to 77 K. Circulation cooling tests at different temperatures were performed to investigate operating conditions, and heat losses under alternating-current (AC) load conditions were measured. The results of performance correlated with cooling test will be presented in this paper.

A Study on the Measurement of Volume and Surface Electrical Conductivity of Cryogenic Insulants for DC HTS Equipment

For the insulation design of dc high-temperature superconducting (HTS) equipment, dc electric field analysis should be performed. As the dc electric field distribution is mainly determined by the relative electrical conductivities of the various insulating materials used, the conductivities of these materials should be precisely measured. In particular, in cryogenic environment, the measurement of electrical conductivity could not be easily conducted due to the difficulty of measuring extremely low leakage current. In this paper, investigation on the measurement of volume and surface electrical conductivity of various cryogenic insulants, including polypropylene laminated paper (PPLP), Kraft, and glass fiber reinforced plastic (GFRP), was carried out. For the measurement of volume electrical conductivity in LN2, the infiltration of LN2 into the specimen should be considered in order to avoid inaccurate measuring data. Thus, in order to increase the reliability for volume electrical conductivity, the PPLP specimen deposited by copper was adopted, and the comparison between ordinary PPLP and PPLP with copper deposition was made. As a result, it was suggested that the copper deposition could be a valid method to prevent the infiltration of LN2 when the electrical conductivity of thin paper was measured. Consequently, volume and surface electrical conductivity values of PPLP, Kraft, and GFRP have been measured and summarized.

PERFORMANCE TEST OF COOLING SYSTEM FOR KEPCO HTS POWER CABLE

A cooling system for a 3-phase 100-m HTS power cable with 22.9kV/1.25kA was installed and tested at the KEPCOs Gochang power testing center in Korea. The system consists of a liquid nitrogen decompression cooing system with a cooling capacity of 3kW at 66K and a closed circulation system of subcooled liquid nitrogen. Several cooling performance tests of the cable system such as cooling capacity, heat load, AC loss and temperature stability, were performed at operating temperature of 66.4K. Thermal cycle test which is cool-down to liquid nitrogen temperature and warm-up to room temperature, was also performed to investigate thermal cycle influences. This paper describes the installed cooling system, temperature stability and heat load test results.

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.

Field Test of 3 phase, 22.9kV, 100m HTS Cable System in KEPCO

Starting from investigation of feasibility and basic studies, KEPCO/KEPRI has carried an enterprising project for HTS cable system since 2002. The objectives of this project are to demonstrate HTS cable system and evaluate the feasibility in electricity utilitys view. The installation of 100m/3phase/22.9kV/50MVA HTS cable system is undergoing in KEPCOs test yard, located in Gochang, Korea. The HTS cable system consists of 100m long cable, two terminations and a cooling system. To simulate the actual cable installation, the 55m section of the 100m long cable was installed into an underground tunnel. Commissioning test is scheduled at the end of September, 2005 and followed by long term operation test. In this paper, the installation of HTS cable system and initial results of system operation will be summarized