Song-Ho Sohn

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.

Installation and Power Grid Demonstration of a 22.9 kV, 50 MVA, High Temperature Superconducting Cable for KEPCO

Korea Electric Power Corporation (KEPCO) has a great interest on the application of HTS cable to its network to relieve power congestion and enhance the reliability of the power system. Down through the years from 2005 to 2010, the 22.9 kV, 50 MVA HTS cable has been demonstrated by field test, showing affirmative results. With the financial support of Ministry of Knowledge and Economy (MKE), the new project to install and operate the HTS cable in electrical network of Korea was launched in 2008. An HTS cable with the 22.9 kV, 50 MVA, and 410 m length was installed in the KECPO grid in the end of 2010. After the integration of the HTS cable system, the commissioning items of the DC withstand voltage test, DC critical current test, and heat loss measurements were conducted in accordance with the Korean industrial standard, and self-defined specifications. The HTS cable was energized on the 154 kV Icheon substation of KEPCO on August 19th, 2011. The details of the project description, onsite installation, and commissioning tests are presented in this paper.

Hybrid Cooling System Installation for the KEPCO HTS Power Cable

In Korea, the KEPCO (Korea Electric Power Corporation) HTS power cable system has been successfully operated for evaluating the technical and economic feasibility as well as accumulating the operation experience since 2006. A cooling system composed of a liquid nitrogen decompression cooling unit and a closed-circulation system of subcooled liquid nitrogen at the KEPCOs Gochang power testing center. As the next step, we adjusted the cooling system for the purpose of testing a different cooling system using a cryocooler unit with cooling capacity of 4 kW at 77 K in the existing cooling system. It was designed to be used as a hybrid cooling system. In other words, it has as an each system of cryocooler unit or decompression pump unit. In this paper, the performance test results are summarized and the outline of the hybrid cooling system is introduced.

Application of Resistive Type SFCL to Protect Bi-2223/Ag Tape Against AC Over-Currents

Based on the electrical behavior of Bi-2223/Ag tape in transient state, the possibility of SFCL application was investigated as a fundamental study for the protection of HTS power apparatus. For the experiments, the Bi-2223/Ag tape having the critical current of 56 A and the resistive type SFCL fabricated using three elements of YBCO thin films were examined. When the applied current exceeds the rated current of the SFCL, the current was limited to sufficiently low level, however, higher than 40 Vrms was not allowed considering power density of SFCL. On the other hand, as a method to increase the power density, a shunt resister across the SFCL was adopted to increase the allowed power density. In this case, the results showed that the over current was limited below the safe range for HTS tape and the SFCL was safe, although 100 Vrms was applied to the circuit. In conclusion, the switching power capacity of a SFCL could be increased by using a shunt resistor, and HTS tape could be protected safely within the quench margin

Cryogenic System for 80-kV DC HTS Cable in the KEPCO Power Grid

DC HTS cable has advantages in the absence of ac loss. Therefore, the Korea Electric Power Corporation (KEPCO) has started a project of operating and manufacturing technology for applying an 80-kV 500-MW 500-m-long dc HTS cable to the commercial power grid since 2011. LS Cable Ltd. has joined this project for designing and manufacturing an HTS power cable, and KEPCO has taken on cryogenic system and real power grid operation. The cryogenic system for an 80-kV dc HTS cable is composed mainly of Stirling-type cryocoolers. The Stirling cryocooler has been examined and verified by real grid operation in Icheon substation, and we therefore became assured of reliability for the cooling HTS cable system. We present the cryogenic system design, installation, and some results of preliminary tests in this paper.

Progress on the Performance Test of KEPCO HTS Power Cable

The Korea Electric Power Corporation (KEPCO) HTS power cable has been successfully installed and operated for feasible confirmation since 2006 at Gochang power test center. The 3-phase 100 m long HTS power cable with 22.9 kV/1.25 kA was manufactured and cooled by subcooled liquid nitrogen. At the beginning stage, the cooling system was composed of a liquid nitrogen decompression cooling unit. No major fault has been observed during long term operating test. As a next step, cooling system was modified that a cryocooler was employed, resulting in the total cooling capacity of 4 kW at liquid nitrogen temperature. In this paper, the progress on the performance test of HTS power cable is reported. Temperature as well as pressure in the system is discussed with respect to the supplied current levels. Also, the installation of hybrid cooling system for real power grid application is described.

Performance Test of Cooling System for 500 m HTS Cable in KEPCO Power Grid

The high temperature superconducting (HTS) power cable has been successfully installed and operated for feasibility confirmation since 2006 at the power testing center of Korea Electric Power Corporation (KEPCO). The three phase 100 m long HTS cable with 22.9 kV/1.25 kA was manufactured and cooled by the open-loop of sub-cooled liquid nitrogen generated by a decompression cooling unit. No major fault has been observed during long-term operating test. As a next step, the design study of a 500 m long HTS cable system has initiated in 2008. Now, the HTS power cable was manufactured and installed at Icheon substation located near Seoul. In this paper, the cooling performance test of the 500 m long HTS cable in the real power grid is reported. Pre-cooling process using nitrogen gas is presented and the result of initial cool-down of the HTS cable is reported. Also, temperature as well as pressure drop in the system is discussed with respect to the loading current level.

Quench Development Due to External Magnetic Field in HTS Cable Conductor Transporting AC Current

In this study, a prototype HTS cable conductor with 1 layer of 10 Bi-2223/Ag tapes was fabricated and the quench development due to the influence of external magnetic fields was investigated. Firstly, AC current whose peak value amounts around two times critical current was applied to the HTS cable conductor. From the experiments, the influence of self field was considered to be small enough not to affect the transporting characteristics. Secondly, external magnetic fields of 50 and 100 mT were applied to the HTS cable conductor transporting AC current. In this case, due to the directional dependence of Bi-2223/Ag tapes on magnetic field, various magnitudes of voltages were detected in each strand. Finally, the quench development with the magnitude of the applied external magnetic field was analyzed

AC Loss Characteristics of a Single-layered Cylindrical High Temperature Superconductor

The AC loss is an important issue in the design of the high temperature superconductor (HTS) power cables and fault current limiters. In these applications, a cylindrical HTS conductor is often used. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analyzed. The result show that the measured losses for two conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with low critical current density is in good agreement with the calculated loss from Monoblock model, whereas the loss measured for the Bi-2223 conductor with high critical current density doesn`t coincide with the loss calculated from the Monoblock model. The measured loss is also different from numerically calculated one based on the polygon model especially in low transport current.