Hun-Chul Seo

Superconducting Fault Current Limiter Application for Reduction of the Transformer Inrush Current: A Decision Scheme of the Optimal Insertion Resistance

A conventional superconducting fault current limiter (SFCL) is usually only connected to a power system for fault current limitation. The study described in this paper, however, attempts to use the hybrid SFCL application to reduce the transformer inrush current. To accomplish this, this paper first suggests the concepts to expand the scope of the SFCL application in the power system. The power system operator should first determine the proper amount of current-limiting resistance (CLR) of the hybrid SFCL. Therefore, this paper suggests a decision scheme of the optimal insertion resistance in an SFCL application to reduce the transformer inrush current. This scheme and the SFCL model are implemented using the electromagnetic transient program (EMTP). We determine the optimal CLR by EMTP simulation, and this value is applied to model the SFCL by the EMTP. The simulation results show the validity and effectiveness of the suggested scheme and the ability of the SFCL to reduce the inrush current.

Analysis of the Neutral Current for Two-Step-Type Poles in Distribution Lines

One-step-type poles and two-step-type poles are used in KEPCOs distribution system. An unbalanced current may flow through the neutral wire in three-phase four-wire distribution systems due to unbalanced loads. Generally, the power line and the communication line are installed in close proximity due to the topography of Korea. By means of electrostatic induction, electromagnetic induction, and harmonic induction, the power line induces damaging voltage and current in the communication line. This paper calculates the neutral current in KEPCOs distribution system by using the electromagnetic transients program (EMTP) by composing various simulated conditions, and the results are verified by vector analysis.

An Adaptive Autoreclosure Scheme with Reference to Transient Stability for Transmission Lines

Autoreclosure provides a means of improving power transmitting ability and system stability. Conventional reclosure adopts the fixed dead time interval strategy, where the reclosure is activated after a time delay to restore the system to normal as quickly as possible without regard to the system conditions. However, these simple techniques cannot provide optimal operating performance. This paper presents an adaptive autoreclosure algorithm including variable dead time, optimal reclosure, phase-by-phase reclosure and emergency extended equal-area criterion (EEEAC) algorithm in order to improve system stability. The reclosure algorithm performs the operations that are attuned to the power system conditions. The proposed adaptive reclosure algorithm is verified and tested using ATP/EMTP MODELS, and the simulation results show that the system oscillations are reduced and the transient stability is enhanced by employing the proposed adaptive reclosure algorithm.

Dynamics of grid-connected photovoltaic system at fault conditions

Use of an environmentally clean photovoltaic (PV) power generation system will become more widespread in the future due to anticipated cost reduction in PV technology. As the capacity of PV systems increases, the stable output of the grid-connected PV system becomes important. However, the output variation of PV systems is dependent on the faults and transients of the power system. This paper analyzes the dynamics of a PV system at fault conditions. A 3 MW PV system is modeled by Matlab/Simulink, and then the distribution system with the PV system is modeled. This paper simulates the various fault types, and analyzes the output of the PV system at fault conditions. The results show that output of the PV system depends on the fault type.

Algorithm for Fault Detection and Classification Using Wavelet Singular Value Decomposition for Wide-Area Protection

An algorithm for fault detection and classification method for wide-area protection in Korean transmission systems is proposed. The modeling of 345-kV and 765-kV Korean power system transmission networks using the Electro Magnetic Transient Program - Restructured Version (EMTP- RV) is presented and the algorithm for fault detection and classification in transmission lines is developed. The proposed algorithm uses the Wavelet Transform (WT) and Singular Value Decomposition (SVD). The Singular value of Approximation coefficient (SA) and part Sum of Detail coefficient (SD) are introduced. The characteristics of the SA and SD at the fault conditions are analyzed and used in the algorithm for fault detection and classification. The validation of the proposed algorithm is verified by various simulation results.

The analysis of power quality effects from the transformer inrush current: A case study of the Jeju power system, Korea

The transformer inrush current can cause a voltage drop by source impedance. This current can impact sensitive loads by the voltage drop. Therefore, it is necessary to take measures to limit this inrush current. Accurate modeling and analysis for inrush current is the first step in developing a technique to take practical measures. This study, described in this paper, analyzes the power quality affected by transformer inrush current using the Jeju power system in Korea. The Electromagnetic Transients Program (EMTP) is used to analyze the transient phenomenon. We discuss a method to model the hysteresis curve of the transformer in EMTP. We carried out various simulations to analyze the power quality during transformer energization. The analysis results of voltage drop by the inrush current occurrence when certain requirements are met are presented.

Analysis of Magnitude and Rate-of-rise of VFTO in 550 kV GIS using EMTP-RV

Very Fast Transients (VFT) originate mainly from disconnector switching operations in Gas Insulated Substations (GIS). In order to determine the rate-of-rise of Very Fast Transient Overvoltage (VFTO) in a 550 kV GIS, simulations are carried out using EMTP-RV. Each component of the GIS is modeled by distributed line model and lumped model based on equivalent circuits. The various switching conditions according to closing point-on-wave and trapped charge are simulated, and the results are analyzed. Also, the analysis of travelling wave using a lattice diagram is conducted to verify the simulation results.

Development of Adaptive Reclosing Scheme Using Wavelet Transform of Neutral Line Current in Distribution System

Abstract This article proposes an adaptive operating scheme for a recloser based on classified detection of transient faults and permanent faults in a distribution system. Wavelet transform is used to classify whether a fault is transient or permanent in nature. The Haar mother wavelet of the current flowing in a neutral line has more rich harmonics than other mother wavelets, such as Daubechies, Symlets, Coiflets, and Biorthogonal, so the total harmonic distortion of the Haar mother wavelet is applied for estimating the instant of fault clearance and giving a signal for operating action to the recloser (reclosing). The various simulations according to the fault clearance time and fault type are performed using the Electromagnetic Transient Program to verify the proposed algorithm. The simulation results show the effectiveness of the proposed algorithm.

Development of a Reclosing Scheme for Reduction of Turbine Generator Shaft Torsional Torques: A Decision Method to Achieve Optimal Reactor Capacity

It is well known that line switching operations like reclosing are able to cause transient power oscillations which can stress or damage turbine generators. This paper presents a reclosing scheme to reduce the shaft torsional torques of turbine generators by inserting an additional reactor. A novel method to determine optimal reactor capacity to minimize the torsional torque generated in a turbine generator is also proposed. In this paper, the turbine generator shaft is represented by a multi- mass model to measure torsional torques generated in the shaft between the turbine and the generator. Transmission systems based on actual data from Korea are modeled to verify the proposed scheme using ElectroMagnetic Transient Program (EMTP) software. The simulation results clearly show the effectiveness of the proposed scheme and torsional torque can be minimized by applying the proposed scheme.

Analysis of Stability of PV System using the Eigenvalue according to the Frequency Variation and Requirements of Frequency Protection

Use of photovoltaic (PV) power generation system will become more widespread in the future due to anticipated cost reduction in PV technology. As the capacity of PV systems increases, a variation of power system frequency may prevent the stable output of PV system. However, the standard for the frequency protection of distributed generation in Korea Electric Power Corporation (KEPCO)s rule does not include the setting of frequency protection. Therefore, this paper analyzes the correlation between the frequency protection requirements and the stability of grid-connected PV system for the adjustable operating setting of frequency protection. The distribution system interconnected with 3 MW PV system is modeled by Matlab/Simulink. The various values of frequency are simulated. For studied cases, the stability of PV system is analyzed. It is concluded that the setting of frequency protection is necessary to consider the stability of PV system.