Ji-Kyung Park

A Novel Reclosing Algorithm Considering Turbine-Generator Shaft Torque

Various factors exist that cause torsional interaction, such as subsynchronous resonance and switching effects following electrical disturbances. In particular, successive circuit-breaker operation may amplify the turbine-generator shaft torque under unsuccessful reclosing conditions. Thus, in this paper, we carried out transient stability analysis using the integral square error method and derived the relationship between the shaft torque amplitude and reclosing time through analysis of a 2-degree of freedom system under reclosing into permanent fault condition. In addition, we proposed a novel reclosing algorithm with consideration of transient stability and shaft torque amplitude. The performance of the proposed reclosing method was verified in actual 154 kV and 345 kV Korean study systems using the Electromagnetic Transient Program.

Battery Energy Storage System-Based Stabilizers for Power System Oscillations Damping

To ensure secure and reliable operations of power systems, rapid damping of power system oscillations is unavoidable. This paper addresses the improved damping characteristics of a power system by integrating the Energy Storage System (ESS) such as a battery into a Flexible AC Transmission System (FACTS) device named the Battery Energy Storage System (BESS). Design of the BESS-based stabilizers is created to enhance the power system dynamic stability and damping profile. A modified Philips-Heffron model of a Single Machine Infinite Bus bar (SMIB) power system with BESS is established and analyzed. Improved damping characteristics of the power system oscillations are selected as performance criteria for the proposed design. Simulation results show the superior performance of the proposed design as compared to the coordinated design of BESS and conventional Power System Stabilizers (PSS). All the simulations are carried out in MATLAB/SIMULINK.

Analysis of Secondary Arc Extinction Effects according to the Application of Shunt Reactor and High Speed Grounding Switches in Transmission Systems

When secondary arc is caused by single phase tripping, arc should be extinguished prior to high speed reclosing which can make the system restore. In this paper, we analyzes secondary arc extinction by applying two methods that are shunt reactor and High Speed Grounding Switches (HSGS). To verify the effects of these methods in arc extinction aspects, two factors are discussed. One is secondary arc extinction time, and another is recovery voltage. Especially, secondary arc waveform and amplitude value are analyzed to identify the effects of arc extinction methods. Simulation is conducted by using ElectroMagnetic Transient Program (EMTP) based on actual Korea 765kV transmission system.

Development of an Adaptive Under-Excitation Limiter in Excitation System

A generator is designed to operate in the underexcitation region within its capability according to the system conditions. However, a sustained underexcitation condition owing to the partial and complete loss-of-field in the generator can cause thermal damage and system instability. Thus, an automatic voltage regulator and an underexcitation limiter should control the underexcitation condition of the generator, and the loss-of-field relay should be utilized to guarantee reliable operation. Therefore, in this paper, we discuss the coordination of generator underexcitation protection among various factors. In addition, in order to enhance the conventional underexcitation limiter, we proposed an adaptive underexcitation limiter. Through this method, a possibility of miscoordination can be avoided and the operation is modified adaptively according to the loss-of-field condition. The performance of the proposed method was verified via a 345-kV Korean nuclear power plant and transmission system using the Electromagnetic Transients Program.

A Study on Optimal Sequential Reclosing to Improve Transient Stability in Transmission System

In transmission system, reclosing scheme is very useful method to improve continuity of power supply and reliability of system. Especially, high speed reclosing which is used generally in transmission systems has a benefit improving transient stability. However, the reclosing can jeopardize the stability under the condition having high difference of voltage phase angle between both ends. Thus, this paper proposes optimal sequential reclosing scheme to improve transient stability due to reclosing operation. The optimal sequential reclosing is that each phase is closed sequentially considering transient energy. In this paper, 345kV and 154kV transmission system is modeled using EMTP (ElectroMagnetic Transient Program) to verify the performance and effectiveness of optimal sequential reclosing on transient stability. Also, Integral Square Error(ISE) method is used to assess the transient stability.