Suchul Nam

Design of Advanced Voltage Management System Including Manual Operation Mode via Real-Time Digital Simulator

This paper presents the design of the advanced voltage management system (AVMS) including manual operation mode in order to control reactive power generation in a practical power system. The existing secondary voltage controller (SVC) has a demerit occurring as a large transient phenomenon shortly after the SVC begins to work. This malfunction results from the difference of the operation statuses before and after the SVC operates. For solving the problem and implementing the voltage control safely, the AVMS including the manual operation mode is developed by Korea Electric Power Corporation. Aside from the fact that the AVMS overcomes the drawback, it can also execute the coordination control of both continuous voltage controller (CVC) and discrete voltage controller (DVC). The CVC controls reactive power generation sources such as generator and flexible ac transmission system devices which can generate reactive power continuously and linearly. On the other hand, the DVC controls the discrete reactive power sources such as switched shunt capacitors and reactors. The performances of the proposed AVMS are carried out by time-domain simulation in the Jeju Island power system with real-time digital simulator.

A Practical Power System Stabilizer Tuning Method and its Verification in Field Test

This paper deals with parameter tuning of the Power System Stabilizer (PSS) for 612 MVA thermal power plants in the KEPCO system and its validation in a field test. In this paper, the selection of parameters, such as lead-lag time constants for phase compensation and system gain, is optimized using linear and eigenvalue analyses. This is then verified through the time-domain transient stability analysis. In the next step, the performance of PSS is finally verified by the generators on-line field test. After the field test, measured and simulated data are also compared to prove the effectiveness of the models used in the simulations.

A Tuning Method for the Power System Stabilizer of a Large Thermal Power Plant and Its Application to Real Power System : Part I-Selection of Parameters by Off-line Simulation

This paper, which consists of two parts, dealt with the parameter tuning of the power system stabilizer for a 612[MVA] thermal power plant in KEPCO system and its validation in field test. In Part 1 of the paper, the selection of parameters such as lead-lag time constants for phase compensation, system gain was optimized by using linear & eigenvalue analyses and they were verified through the time-domain transient stability analysis. In part 2, the performance of PSS was finally verified by the generator`s on-line field test. Through the comparisons of simulation results and measured data before and after tuning of the PSS, the models of generator and its controllers including AVR, Governor and PSS used in the simulation are validated and confirmed.

A Tuning Method for the Power System Stabilizer of a Large Thermal Power Plant and Its Application to Real Power System : PART II - Field Tests and Verification of PSS Performance

【This paper, as the second part of the paper, dealt with the field test and test results to validate PSS(Power System Stabilizer) parameters which are previously tuned in Part 1 paper. In Part 1 of the paper, the selection of parameters such as lead-lag time constants for phase compensation and system gain was optimized by using linear & eigenvalue analyses and they were verified through the time-domain transient stability analysis. In part 2, the performance of PSS was finally verified by the generators on-line field test. Through the comparisons of simulation results and measured data before and after tuning of the PSS, the models of generator and its controllers including AVR, Governor and PSS used in the simulation are verified and confirmed.】

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.

Development of long-term simulator for the large-scaled power system

This paper presents a development of program in long-term dynamic stability. The long-term voltage instability is caused by reactive-power reserves. The reactive-power reserve problems are especially determined by Over-excitation limiter(OXL) and Under Load Tap Changer(ULTC), etc., which are the power device having a few to 10s minutes of time periods. The previous method estimating Long-term voltage stability is the Full-time domain simulation. The Full time simulation methods can compute the exact results, but it may take an amount of time to simulate. And it may have the numerical error in long-term time scale. Thus, the alternative methods to calculate the appropriate results are needed. This paper deals with the Long-term voltage stability using Quasi-Steady-State (QSS) Analysis. QSS can provide good results and improve the speed of simulation. This fast time simulation method (QSS) assumes that the short-term dynamics or transient stability are stable after the contingency and can be replaced by their equilibrium equations. The concept of singular perturbation is applied on focus on long-term dynamics.

A Study on the Method to Evaluate Minimum Capacity of Energy Storage System(ESS) for Micro Grid(MG) Design

In this paper, we propose a probability method to determine minimum capacity of energy storage system(ESS) for Micro-grid Because of high capital cost of ESS, It`s very important to determine optimal capacity of ESS and for stable operation of Micro grid(MG), we should determine minimum capacity of ESS. The proposed method has abilities to consider forced outage rate of generators and intermittent of non-dispatchable generators and minimum capacity make MG keep energy balancing by oneself.

Field Implementation of Voltage Management System (VMS) into Jeju Power System in Korea

This paper presents the results of field tests on Voltage Management System (VMS) using hybrid voltage control, which utilizes coordinated controls of various reactive power resources such as generators, FACTS and switched shunt devices to regulate the pilot bus voltage in a voltage control area. It also includes the results of performance test on RTDS-based test bed in order to validate the VMS before installing it in Jeju power system. The main purpose of the system is adequately to regulate the reactive power reserve of key generators in a normal condition with coordination of discrete shunt devices such as condensers and reactors so that the reserves can avoid voltage collapse in emergency state in Jeju system. Field tests in the automatic mode of VMS operation are included in steady-states and transient states. Finally, by the successful operation of VMS in Jeju power system, the VMS is proved to effectively control system voltage profiles in steady-state condition, increase system MVAR reserves and improve system reliability for pre- and post-contingency.

Modeling and Simulation about Long Term Dynamics Using Real Time Digital Simulator

RTDS (Real Time Digital Simulator) has several benefits. First, current power system simulation tool dose not simulate electromagnetic transient phenomenon, but it is possible using RTDS. Second, off-line electromagnetic transient simulation tools (EMTDC, PS-CAD, etc.) do not simulate real-time analysis, but RTDS is able to do real-time analysis. Third, RTDS is able to simulate related external devices those are protection relays, new developed control devices and power system devices. So many engineers use RTDS in power industry using these advantages of RTDS. KEPCO (Korea Electric Power Corporation) also use RTDS for developing new special protection scheme that is a new developed protection scheme for maintaining voltage stability in metropolitan area using real time synchro phasor data. Voltage stability phenomena of power system are divided three parts by time period. Those are transient, short term and long term voltage stability phenomena. Almost critical voltage stability problems happen in long term time period. Because power system devices and loads those influence voltage stability have long term dynamic characteristic. So if we want correct results of voltage stability analysis, then we have to analyze long term dynamic about voltage stability. Long term dynamic characteristic of voltage stability that is influenced by under voltage tap changer, over excite limiter, dynamic loads and so on. Unfortunately, we had not an analysis environment about long term dynamics for validating new control system. So this paper discusses about modeling and simulation of long term dynamics using RTDS. First, we build well known test system that consists of 2 generators and 11 buses using RTDS. Second, we model dynamic controllers and devices those are under load tap changer, over exciting limiter and dynamic load and we validate those dynamic characteristics. Those influence to long term voltage stability. Lastly, we simulate voltage collapse phenomena during long term time period using test-system include built long term dynamic models when occurring line fault.

Construction of Test-bed with RTDS for Verifying Coordination Algorithm for Loop Distribution System

Presently, most of the normal distribution system configuration is a radial type. When a fault occurs in the radial system, one or more loads experience an outage for a few minutes until the fault is cleared. But if the distribution system is configured with a loop type, then the power can be supplied to all customers without any outage. So, for improving reliability of power supply, the research of the loop distribution system has been performed recently. Previously, At the KEPCO PT Center (PT: Power Testing), several tests like single fault, communication failure, CB open failure, etc, were performed to verify performances of the coordination control algorithm for loop distribution. However, there are some limitations in this field test for overall its functions. For example, a few tests such as a three-phase fault, line to line fault and the Closed-loop Control Device (CCD) internal fault are hard to fulfill in field test. Therefore, it should be tested by Real Time Digital Simulator (RTDS). The RTDS is a fully digital power system simulator in real-time and hence can make an environment similar to physical power system. In this paper, the validity of the coordination algorithm for a loop distribution system is verified with RTDS which is connected with the protection relays called CCD.