Sang-Bong Rhee

Dispersed generator placement using fuzzy-GA in distribution systems

This paper presents a fuzzy-GA method to resolve dispersed generator placement for distribution systems. The problem formulation considers an objective to reduce power loss costs of distribution systems and the constraints with the number or size of dispersed generators and the deviation of the bus voltage. The main idea of solving fuzzy nonlinear goal programming is to transform the original objective function and constraints into the equivalent multi-objectives functions with fuzzy sets to evaluate their imprecise nature and solve the problem using the proposed genetic algorithm without any transformation for this nonlinear problem to a linear model or other methods. Moreover, this algorithm proposes a satisfying method to solve the constrained multiple objective problem. Analyzing the results and updating the expected value of each objective function allows the dispatcher to obtain the compromised or satisfied solution efficiently.

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.

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.

Optimization of novel flux barrier in interior permanent magnet-type brushless dc motor based on modified Taguchi method

This paper proposes the novel flux barrier by using the modified Taguchi method to reduce the cogging torque. In the optimizing process the modified Taguchi method is utilized to consider multiple objective quality characteristics simultaneously such as the torque ripple and the efficiency as well as the cogging torque. The optimal novel flux barrier can effectively reduce the cogging torque and torque ripple and it is verified through the experimental results.

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.

Assessment of total transfer capability subject to transient stability energy margin

This paper presents a method to assess total transfer capability (TTC) by using energy function. TTC assessment is to calculate TTC by using the repeated power flow (RPF) method. TTC is limited not only by the violation of system voltage and thermal limits, but also restricted by transient stability limit. The transient energy margin is the difference between the transient energy and the critical energy. In order to calculate energy margin, two values of the transient energy function have to be computed. The first value is transient energy that is the sum of kinetic and potential energy at the end of fault. The seconds is critical energy that is potential energy at controlling UEP. The method proposed is applied to 4 machines systems to demonstrate its effectiveness.

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.

Optimal rotor design for reducing the partial demagnetization effect and cogging torque in spoke type PM motor

This paper proposes an optimized rotor pole shape that can effectively reduce the partial demagnetization effect and cogging torque. First, for reducing the peak amplitude of the external field that directly affects the partial demagnetization on the permanent magnets in spoke-type permanent magnet motor, we conduct a variation of core shape and insertion of a barrier. Second, with the rotor shape obtained by the first processes for reducing the partial demagnetization effect, another part of the rotor pole is varied to make better sinusoidal distributed air gap flux density to reduce the cogging torque. In the process of designing the rotor pole shape, a steepest descent method and a response surface method are applied for improving convergence. By using the finite element method, we show that the optimized rotor pole shape drastically reduces the effect of the partial demagnetization and cogging torque.

Security constrained OPF by hybrid algorithms in interconnected power systems

This paper presents a hybrid algorithm for solving security constrained OPF in interconnected power systems, which is based on the combined application of evolutionary programming (EP) and sequential quadratic programming (SQP). The efficient algorithm combining main advantages of two methods is as follows: Firstly, EP is applied to perform global exploitation among a population. This gives a good initial point of a conventional method. Then, SQP are used to perform local exploitation. The hybrid approach often outperforms each method operating alone and reduces the total computation time. The objective functions are the minimization of generation fuel costs and system power losses. In OPF considering security, the outages are selected by contingency ranking method. The control variables are the active power of the generating units, the voltage magnitude of the generator, transformer tap settings and SVC setting. The state variables are the bus voltage magnitude, the reactive power of the generating unit, line flows and the tie line flow. The method proposed is applied to the modified IEEE model system.

THD Reduction of Distribution System Based on ASRFC and HVC Method for SVC under EV Charger Condition for Power Factor Improvement

Electric vehicles (EVs) have been gaining popularity in recent years due to growing concerns about fuel depletion and increasing petrol prices. Random uncoordinated charging of multiple EVs at residential distribution feeders with moderate penetration levels is expected in the near future. This paper describes a high performance voltage controller for the EVs charging system, and proposes a scheme of asymmetric synchronous reference frame controller (ASRFC) in order to compensate for the voltage distortions and unbalance distribution system due to EVs charger. This paper explores the power factor of distribution and residential network under random EVs charger on the bus load. ASRFC and harmonic voltage compensator (HVC) are employed for static VAR compensator (SVC) in this paper. The proposed scheme can improve the power factor and total harmonic distortion (THD) of the smart grid due to the EVs charger in grid. The effectiveness of the scheme was investigated and verified through computer simulations of a 22.9-kV grid.