Seong-Woo Yim

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.

Long-Term Operation and Fault Tests of a 22.9 kV Hybrid SFCL in the KEPCO Test Grid

This paper reports on the operation test of a 22.9 kV hybrid superconducting fault current limiter (SFCL) in the KEPCO test grid. The SFCL works at a rated voltage and current of 22.9 kV and 630 A, respectively. There are two major objectives of the operation test: (1) long-term operation and (2) fault tests for protection coordination study. The operation lasted for more than a year. We experienced several times of cryostat suspension due to blackouts and false alarms due to sensor failures during the operation. We also carried out short circuit tests in the test grid, equipped with circuit breakers and a recloser. An artificial fault generator was used to generate fault currents. The tests showed that the SFCL, together with the recloser, functioned reliably under repeated faults. We also confirmed the reclosing capability of the SFCL. We have presented herein the operation details, cost of operation, short-circuit test results, and our plans for further tests for protection coordination.

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.

Loss Test for a 5-m YBCO Cable Sample of the 22.9-kV KEPCO System Under Grid Operation

We have operated the 22.9-kV high temperature superconductor cable system installed at Icheon Substation of Korea Electric Power Corporation (KEPCO), which consists of a conductor and a shield using YBCO-NiW wires. We prepared the same 5-m cable sample as the Icheon Substation in order to understand its ac loss characteristic. Especially, the contact resistance between copper current leads and YBCO wires was minimized through the increased soldering surface between them. Besides, four voltage leads are attached to both the conductor and the shield with an equal angle of 90°. Under ac transport current, which was supplied to the conductor and shield in opposite direction, losses of the 5-m sample were tested for various contact positions of voltage leads, frequencies, and transport periods. The result shows that the measured ac losses for various contact positions in the conductor and shield are the same. However, their loss exponents are very different. More details will be presented in this work.

Dynamic Characteristics of a 22.9 kV Hybrid SFCL for Short-Circuit Test Considering a Simple Coordination of Protection System in Distribution Networks

This paper presents the results of short-circuit tests with a 22.9 kV hybrid superconducting fault current limiter (SFCL) on the KEPCO test grid. The hybrid SFCL we used for the test had suffered from lots of field tests including a long term operation and it is still in working order. We have already proved that the SFCL showed high reliability as well as feasibility through a long term operation and short-circuit tests performed before. In this paper, we tried to study a dynamic characteristics of the same SFCL on the distribution power grid through short-circuit tests with a circuit breaker and a reclosing relay. An artificial fault generator (AFG) was used to generate fault currents in the KEPCO power test center. The two objectives of the tests are (1) verifying a precise reaction of the SFCL to reclosing operation and (2) a study for protection coordination with SFCL. The test results showed that the SFCL worked precisely with a fast recovery of the superconducting elements when we applied a one-time reclosing operation with the interval of 0.6 second. We also suggested a proper manipulation of the coordination of the protection system in distribution networks with the SFCL in the paper.

A study of wireless power transfer topologies for 3.3 kW and 6.6 kW electric vehicle charging infrastructure

Inductive wireless power transfer (WPT) systems for electric vehicle (EV) charging applications are designed at 3.3 and 6.6 kW power classes. A comparison of compensation circuits between SS (series - series) and LCL-LCL topologies is carried out. Measurement results of 3.3 kW WPT system show that the SS topology has higher transfer efficiency than the LCL-LCL one with a peak transfer efficiency of 93.1 % and 89.5 % for SS and LCL-LCL topologies, respectively, at a transfer distance of 100 mm. The LCL-LCL topology is more robust than the SS topology in terms of power factor when a misalignment between coils occurs or when the frequency varies. Measurement results of 3.3 kW WPT system are consistent to the circuit simulation. The WPT systems operate at a frequency of 85 kHz.

Condition Based Monitoring of Superconducting Fault Current Limiter Using Fuzzy Support Vector Regression

The superconductor-triggered type fault current limiter (STFCL), which was developed by KEPCO and LS Industrial Systems, is under operation for a verification test at KEPCOs power testing center. The STFCL is composed of a superconductor, a fast switch and a current limiting resistor. In this paper, we investigated the empirical modeling of the STFCL using principal component based and fuzzy support vector regression (PCFSVR) for the prediction and detection of faults in the STFCL. Signals for the model are the currents and voltages acquired from the high-temperature superconductor (HTS), driving coil (DC) and current limiting resistor (CLR). After developing an empirical model, we analyzed the accuracy of the model. The results were compared with those of principal component based support vector regression (PCSVR) as presented in MT21. PCFSVR showed better performance in terms of the average level of accuracy. This model can be used for the condition-based monitoring of STFCL systems to predict any fault symptoms of the system through the advantage of the auto-correction function of the model.