Korea Electric Power Corporation System Research Articles

Extended Geometric Feature Extraction Process for Detecting Multiple Frequency Oscillations in KEPCO System

In this study, a new algorithm dealing with time-varying modes for determining and tracing multiple frequency oscillations in power systems is proposed. Multiple modes or resonance of forced and natural oscillations can have severe effects on a power system. Therefore, it is crucial to recognize the dominant natural and forced oscillations because the oscillation mode possesses time-varying features that depend on the system operating conditions or changes in the parameters. The salient features of the proposed algorithm include the use of a time-series-based approach to recognize undesired modes (including multiple oscillations over a wide frequency range), tracing time-varying modes as the power system operating condition changes, and effectively determining and applying the oscillation features before implementing the corresponding control measures in the power system. In this study, multiple frequency oscillation scenarios for the test system and practical measurement data for a recent incident that occurred in Korea Electric Power Corporation (KEPCO) system are discussed. Therefore, the proposed algorithm can be practically applied in wide-area monitoring systems, not only for a single forced oscillation or local mode detection but also for system-wide inter-area mode recognition.

Analysis of Low Frequency Oscillation Using the Multi-Interval Parameter Estimation Method on a Rolling Blackout in the KEPCO System

This paper describes a multiple time interval (“multi-interval”) parameter estimation method. The multi-interval parameter estimation method estimates a parameter from a new multi-interval prediction error polynomial that can simultaneously consider multiple time intervals. The root of the multi-interval prediction error polynomial includes the effect on each time interval, and the important mode can be estimated by solving one polynomial for multiple time intervals or signals. The algorithm of the multi-interval parameter estimation method proposed in this paper is applied to the test function and the data measured from a PMU (phasor measurement unit) installed in the KEPCO (Korea Electric Power Corporation) system. The results confirm that the proposed multi-interval parameter estimation method accurately and reliably estimates important parameters.

Detection of low-frequency oscillation using synchrophasor in wide-area rolling blackouts

This paper discusses the rolling blackouts implemented by the Korea Electric Power Corporation (KEPCO) on September 15, 2011, and a low-frequency oscillation that occurred at that time. On the day of the rolling blackout, spectral analysis and mode analysis were performed using the data obtained from a synchrophasor installed in the KEPCO system. Low-frequency oscillation modes near 0.68Hz and 0.5Hz occurring respectively before and during the process of forced load shedding were estimated. These wide-area oscillation modes may cause total blackouts, and may be good indicators of reliable system operation in the event of similar wide-area rolling blackouts in the future.

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.

Determination of available transfer capability (ATC) considering real-time weather conditions

Total Transfer Capability (TTC) should be pre-determined in order to estimate Available Transfer Capability (ATC). Typically, TTC is determined by considering three categories; voltage, stability, and thermal limits. Among these, thermal limits are treated mainly in this paper on the evaluation of TTC due to the relatively short transmission line length of Korea Electric Power Corporation (KEPCO) system. This paper presents a new approach to evaluate the TTC using the Dynamic Line Rating (DLR) for the thermal limit. Since the approach includes not only traditional electrical constraints but also real-time environmental constraints, this paper obtains more cost-effective and exact results. A case study using KEPCO system confirms that the proposed method is useful for real-time operation and the planning of the electricity market. Copyright © 2010 John Wiley & Sons, Ltd.

Assessment of Available Transfer Capability (ATC) considering Real-time Weather Conditions

Total Transfer Capability (TTC) should be pre-determined in order to estimate Available Transfer Capability (ATC). Typically, TTC is determined by considering three categories; voltage, stability and thermal limits. Among these, thermal limits are treated mainly in this paper on the evaluation of TTC due to the relatively short transmission line length of Korea Electric Power Corporation (KEPCO) system. This paper presents a new approach to evaluate the TTC using the Dynamic Line Rating (DLR) for the thermal limit. Since the approach includes not only traditional electrical constraints but also real-time environmental constraints, this paper obtains more cost-effective and exact results. A case study using KEPCO system confirms that the proposed method is useful for real-time operation and the planning of the electricity market.

Application of Multi-step Undervoltage Load Shedding Schemes to the KEPCO System

This paper deals with improvements to the special protection schemes (SPS) which have been applied to the low probability and high impact contingencies in the Korea Electric Power Corporation (KEPCO) system since 2004. Among them, the SPS for voltage instability in the Seoul metropolitan area is considered in this paper, and is a form of event-based undervoltage load shedding with a single-step scheme. Simulation results based upon a recent event that occurred on 765kV lines show that the current setting values of the SPS have to be revised and enhanced. In addition, by applying response-based multi-step undervoltage load shedding (UVLS) schemes to severe contingencies in the system, more effective results than those of the existing single-step SPS can be obtained. Centralized and distributed UVLS schemes are considered in the simulation. ULTC-based load recovery models and over excitation limiters (OXL) for the KEPCO system are also included in the long-term voltage instability studies.

Structure and operation strategies of an automatic supervisory control system for the KEPCO UPFC

The Korea Electric Power Corporation (KEPCO) unified power flow controller (UPFC) is installed at the 154 kV Kangjin substation and is operated on the Kangjin–Jangheung transmission line. This UPFC has been operated by the manual set-point control method; however, it is very difficult for the operator to determine the operation point of UPFC in real-time. This paper proposes an automatic supervisory control system for the KEPCO UPFC to overcome the limitations of set-point control and increase the efficiency of UPFC. The functions and configuration of the system are described and the operation scheme that will be applied in the system is presented. In order to validate the proposed algorithm, a prototype program is developed and some simulations are conducted using the data collected from the load dispatch center in the KEPCO system.

A Special Protection Scheme Against a Local Low-Voltage Problem and Zone 3 Protection in the KEPCO System

This paper presents a special protection scheme, which was established in the KEPCO (Korea Electric Power Corporation) system, against a critically low voltage profile in a part of the system after a double-circuit tower outage. Without establishing the scheme, the outage triggers the operation of a zone 3 relay and trips the component. This sequence of events possibly leads to a blackout of the local system. The scheme consists of an inter-substation communication network using PITR (Protective Integrated Transmitter and Receiver) for acquisition of the substations' data, and under-voltage load shedding devices. This paper describes the procedure for determining the load shedding in the scheme and the experiences of the implementation.

Improvement of the Voltage Difference Method to Detect Arcing Faults Within Unfused Grounded-Wye 22.9-kV Shunt Capacitor Bank

This paper presents an effective algorithm to protect unfused 22.9-kV shunt capacitor banks in grounded-wye connection by improving an existing voltage difference method-based algorithm. It has often been reported that it is difficult to detect ground faults with arc near the input points within the bank using existing algorithms that use only the magnitude of the differential voltage. In this paper, it is shown that ground faults with arc near the input point can be detected by fast Fourier transform (FFT) analysis of the differential voltage and that the proposed algorithm is not impacted by harmonics generated by nonlinear loads which have quantitative influence on the capacitor banks. Consequently, the proposed method using harmonics analysis can be applied as an extended version of the existing detection method. The proposed method is applied to a simplified 22.9-kV real-life Korea Electric Power Corporation system and it is verified that the proposed algorithm can clearly detect faults that are not easily detected by the existing method

Reliability Evaluation of Power Distribution Systems Considering the Momentary Interruptions

In this paper, we propose the reliability evaluation method of power distribution systems considering the momentary interruptions. The results of research are concentrated on two parts. One is the reliability evaluation method of power distribution system considering the momentary interruptions and the other is the reliability cost evaluation that unifies the sustained and momentary interruption costs. These proposed evaluation methodologies are divided into the analytic and probabilistic method. Time Sequential Monte Carlo method is used for the probabilistic methodology. The proposed methods are tested using the modified RBTS (Roy Billinton Test System) form and historical reliability data of KEPCO (Korea Electric Power Corporation) system. Through the case studies, it is verified that the proposed reliability cost evaluation can be used to evaluate the actual reliability.

Strategies to Increase Transfer Limit in Terms of Voltage Stability

This paper presents strategies to enhance transfer limits in terms of voltage stability. First, this paper discusses defInitions of transfer capability and transfer limits as well as their determination. In fact, adequate concept of transfer capability and transfer limit needs to be selected depending on power industry structure. Presently, Korea power market basically uses concept of transfer limits of interface lines for congestion managemen. Also, this paper describes strategies of enhancing transfer limits of systems using OPF formulations. In numerical simulation, an example of KEPCO (Korea Electric Power Corporation) system is shown.

A Study on Determination of Interface Flow Limits in the KEPCO System Using Modified Continuation Power Flow (MCPF)

This paper reports a study on determining the steady-state voltage stability limit of interface flow on a set of interface lines between the metropolitan region and the neighboring regions in the Korea Electric Power Corporation (KEPCO). The interface flow limit considering severe contingencies is determined with a concept of interface flow margin, which is the active power flow margin of the key transmission lines between one region and others under a fixed load demand condition. The paper proposes a procedure to determine secure limit of active power flow on a set of specified interface lines. The procedure uses the modified continuation power flow (MCPF) tracing a path of power flow solutions with respect to generation shift to vary interface flow. In simulation, voltage stability limits of the metropolitan interface flow of the 1998 KEPCO system are determined.

A study on determination of interface flow limits in the KEPCO system using modified continuation power flow (MCPF)

This paper reports a study on determining the steady-state voltage stability limit of interface flow on a set of interface lines between the metropolitan region and the neighboring regions in the Korea Electric Power Corporation (KEPCO). The interface flow limit considering severe contingencies is determined with a concept of interface flow margin, which is the active power flow margin of the key transmission lines between one region and others under a fixed load demand condition. The paper proposes a procedure to determine secure limit of active power flow on a set of specified interface lines. The procedure uses the modified continuation power flow (MCPF) tracing a path of power flow solutions with respect to generation shift to vary interface flow. In simulation, voltage stability limits of the metropolitan interface flow of the 1998 KEPCO system are determined.