Jong-Fil Moon

Current Limiting and Recovery Characteristics of SFCLs Using Magnetic Coupling of Two Coils

Superconducting fault current limiters (SFCLs) using magnetic coupling of two coils can be divided into the insulated type SFCL and the non-insulated type SFCL depending on whether the two coils are insulated through one iron core or not. Among such SFCLs, the transformer type SFCL belongs to the insulated type SFCL because of its insulated two coils. On the other hand, the flux-lock type SFCL, its two coils electrically connected in parallel or series, can be classified into the non-insulated type SFCL. Basically, the structural component and the operational principle of these SFCLs rely upon the magnetic coupling of two coils, and might therefore be considered to be the same. However, there are important differences in the current limiting and the recovery characteristics of these SFCLs depending on design conditions such as the winding direction and the inductance ratio between two coils.

North-East Asia interconnection scenario map, and power reserve strategy in South Korea

The purpose of This work is to obtain the reserve power for the future power shortages faced by the metropolitan areas of the Korean Peninsula and by the southeastern area of the South Korea in North-East Asia. The assumed scenarios will be proposed in the cases of without or with connection to the Sinpo nuclear power plant which is to be constructed with 2,000 MW capacity in the future. In this connection, the types of a power transmission for interconnection consist of the 765 kV HVAC and the HVDC. Here, the various scenarios for providing the interconnection of the power systems among Far-East Russia, North-East China, North Korea, South Korea, and Japan are presented, and the resulting interconnected power systems are simulated by means of a power flow analysis performed with the PSS/E tool. The power flow map is drawn from the data simulated and the comparative study is done.

Quench and Recovery Characteristics of a SFCL Applied Into Neutral Line of a Three-Phase Power System

We suggested that the neutral line is a more effective location for a superconducting fault current limiter (SFCL) in a three-phase power system. To confirm it, we analyzed the quench and recovery characteristics of SFCL applied into the neutral line in cases of non-symmetrical ground faults, such as single line-to-ground and double line-to-ground faults. Through a comparative analysis based on the experimental results for two SFCLs applied either to the neutral line or to the three-phase power line, it was confirmed that the SFCL applied into the neutral line of the power system was more advantageous from the viewpoint of both the practical use of the SFCL and the SFCLs coordination with other related protective devices in the power system.

Voltage Sag Analysis in Loop Power Distribution System With SFCL

In this paper, the effects of a superconducting fault current limiter (SFCL) installed in loop power distribution systems on voltage sags are assessed and analyzed. The power distribution system will be operated to a type of loop. In this case, voltage drops (sags) are severe because of the increased fault current when a fault occurs. If SFCL is installed in the loop power distribution system, the fault current decreases based on the location and resistance value of the SFCL, and voltage sags are improved. In this paper, the improvement of the voltage sag is analyzed according to the fault location, resistance value of SFCL, and the length of the loop power distribution system. First, a resistor-type SFCL model is used using the PSCAD/EMTDC. Next, the loop power distribution system is modeled. Finally, when the SFCL is installed in the radial or loop power distribution system with various lengths, voltage sags are evaluated according to various fault locations. The results of voltage sag analysis in the loop system are compared with the voltage sags in radial power distribution system.

Improvement on Current Limiting Characteristics of a Flux-Lock Type SFCL Using E-I Core

We investigated the current limiting characteristics of a flux-lock type superconducting fault current limiter (SFCL) using an E-I core. Unlike the flux-lock type SFCL using a two-legged common coil (C-C) core, two parallel connected coils and a high-TC superconducting (HTSC) element were placed on the left leg of a three-legged E-I core and an air gap was introduced into the central leg. Through the analyses for the fault current limiting experiments, the two parallel magnetic flux paths was confirmed to be contributed to the prevention of the magnetic saturation of the iron core and the improvement of the current limiting characteristics of the flux-lock type SFCL.

Quantitative Evaluation of the Impact of Repetitive Voltage Sags on Low-Voltage Loads

Automatic reclosing is a typical protection method to clear temporary faults in power distribution systems. However, it has a weakness in regards to voltage sags because it produces repetitive voltage sags. In this paper, we explored the repetitive impacts of voltage sags due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were carried out for obtaining the susceptibility of voltage sags. The final results of the tests yielded the power acceptability curves of voltage sag, and the curves was transformed the 3-D Computer Business Equipment Manufacturer Association (CBEMA) format. For the quantitative evaluation of the impact of repetitive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of repetitive voltage sags.

Time-varying failure rate extraction in electric power distribution equipment

Reliability evaluation of power distribution system is very important to both power utilities and customers. It presents the probabilistic number and duration of interruption such as failure rate, SAIDI, SAIFI, and CAIDI. However, it has a fatal weakness at reliability index because of accuracy of failure rate. In this paper, the time-varying failure rate (TFR) of power distribution system equipment is extracted from the recorded failure data of Korea Electric Power Corporation (KEPCO) in Korea. For TFR extraction, it is used that the fault data accumulated by KEPCO during 10 years. The TFR is approximated to bathtub curve using the exponential (random failure) and Weibull (aging failure) distribution function. In addition, Kaplan-Meier estimation is applied to TFR extraction because of incomplete failure data of KEPCO. Finally, probability plot and regression analysis is applied. It is presented that the extracted TFR is more effective and useful than mean failure rate (MFR) through the comparison between TFR and MFR

Reliability evaluation of distribution system through the analysis of time-varying failure rate

In this paper, the time-varying failure rate (TFR) of power distribution system components is extracted from the recorded failure data of KEPCO (Korean electric power corporation) in Korea and the reliability of power distribution system are evaluated using mean failure rate (MFR) and TFR. The TFR is approximated to bathtub curve using the exponential and Weibull distribution function. In addition, Kaplan-Meier estimation is applied to TFR extraction because of incomplete failure data of KEPCO. Also the reliability of the real power distribution system of Korea is evaluated using the MFR and TFR extracted from real failure data, respectively and the results of each case are compared with each other. As a result, it is proved that the reliability evaluation using the TFR is more realistic than MFR. In addition, it is presented that the application method at power distribution system maintenance and repair using the result of TFR.

A Study on Bus Voltage Sag Considering the Impedance of SFCL and Fault Conditions in Power Distribution Systems

This paper analyzes the bus voltage sags in a power distribution system with a superconducting fault current limiter (SFCL). Among various SFCLs, the composite type with a superconducting element in parallel with a current limiting reactor (CLR) is more effective than resistor-type SFCLs because it reduces the burden on the superconducting element, ac loss, and cost. First, a composite-type SFCL is modeled using PSCAD/EMTDC. Next, a power distribution system with a reclosing protective scheme is modeled. The bus voltage sags depend on the CLR magnitude in the SFCL and the fault period in the power distribution system; the magnitude of voltage sags depends on the magnitude of the fault current, and the durations of the voltage sags depend on the fault period, which is determined by the reclosing time. Therefore, the effects on voltage sags are assessed when an SFCL with various CLR magnitudes is installed in a power distribution system, and the fault duration is changed according to the reclosing time of the protective device.

Study on selection of SFCL's impedance for protection coordination with overcurrent relay in a distribution system

The continuous increase of power demand has resulted in an excess of the rated capacity of the distributed power transformer and the replacement with the larger power transformer is under consideration. However, the larger power transformer has lower impedance, which increases the short-circuit current and exceeds the cut-off-ratings of the circuit breaker in a distribution system. The superconducting fault current limiter (SFCL) has been noticed as the promising method to decrease the short-circuit current in a power system, because it has no power loss in a normal time and can limit the fault current rapidly without additional device to detect the fault current. These merits of the SFCL have made many researchers to adopt the SFCL as one of better solutions to decrease the short-circuit current effectively due to the replacement of the larger power transformer with its lower impedance. However, the protection coordination of the protection devices such as the over-current relay (OCR) and the recloser in a distribution system gets out of the original setting rule due to the introduction of the SFCL. In this paper, we studied on the impedance of the SFCL for the protection coordination with the protection devices in a distribution system. Through the analysis using PSCAD/EMTDC, it was obtained that the range of the impedance of SFCL would be drawn to keep the protection coordination.