Korea Power System Research Articles

Estimation of maximum non‐synchronous generation of renewable energy in the South Korea power system based on the minimum level of inertia

AbstractManaging the output of renewable energy sources considering their uncertainty and variability is crucial for resilience in power system operation. In addition, analyzing stability issues that may arise at the maximum output is important to ensure power system stability. Therefore, the authors propose a method for estimating the maximum non‐synchronous generation (Max NSG) of renewable energy based on the minimum inertia of the power system. The minimum inertia is determined through the correlation between the available and required quantity of inertia and governor resources, satisfying the frequency standards in a South Korean power system. The Max NSG of renewable energy sources at that system inertia level is estimated based on the derived minimum inertia. The proposed method was applied to 22,612 operation data extracted from the Korea energy management system (K‐EMS). The authors estimated a linear relationship between demand levels and Max NSG, ranging from 52.6 to 3.83 GW. The study shows that Max NSG, which is difficult to estimate in many power system operating conditions, can be estimated based on minimum inertia considering the frequency stability in South Korean power systems.

Economic Analysis of Large-Scale Renewable Energy (RE) Source Investment Incorporating Power System Transmission Costs

Recently, the proportion of renewable energy (RE) sources in a power system has been increasing worldwide to reduce carbon emissions. To effectively accommodate renewable energy, there is a growing need to develop integrated planning strategies for both renewable energy sources and transmission lines in a power system, taking into account the location-specific characteristics of renewable energy. Economically viable and rapid system expansion plans are required to resolve the problem of delayed integration of renewable energy into existing power system, which arises due to inadequate transmission facilities. To address these problems, this paper presents an integrated economic evaluation method that considers the inherently uncertain output characteristics of renewable energy, contingent on location, the costs associated with installing transmission lines, and environmental benefits. The case study is conducted using a modified power system in Korea. In the case study, it is assumed that by integrating solar power generators in a low-demand area and wind power generators in a high-demand area, wind power plants have higher construction costs than solar power generators. However, the transmission costs for wind power plants are lower than those for solar power generators due to the regional characteristics of the power grid in the installation areas because renewable energy in high-demand areas typically requires less additional power infrastructure than in low-demand areas. The results of this study show that the net benefit for the wind power plant is estimated at USD 225.4 M, while the solar power plant yields a net benefit of USD 22.9 M in the example system. These results demonstrate the effectiveness of the proposed method, underscoring its potential to mitigate the challenges faced in the practical implementation of renewable energy projects.

Evaluation of inertia resource for securing nadir frequency in HVDC interconnected system with high penetration of RES

For power systems to manage a variety of renewable energy sources while securing system stability and reliability, more resources are required. However, due to the interaction of the frequency response resources, determining the appropriate resources for frequency stability is challenging. In the Jeju system, where two HVDCs control the frequency primarily, this paper suggests a closed-form frequency response prediction model that represents the response characteristics of a high-voltage direct current link (HVDC). The Jeju system has reached its limit as a result of the increased penetration of renewable energy, which has led to increasingly frequent renewable energy curtailments. To ensure the frequency stability of the Jeju power system, it is thought to be necessary to construct a flywheel-connected synchronous condenser. The impact of the inertia constant and capacity of a flywheel-connected synchronous condenser is examined using the proposed closed-form frequency response prediction model. Case studies are presented to demonstrate the feasibility of the proposed method. PSSE simulations are performed with the HVDC user-defined model which manufactured by General Electric (GE) and the Jeju Island power system in Korea. The suggested approach can be successfully applied to choose appropriate resources and plan resources for frequency stability.

How consumers value improving energy efficiency policy in the electricity market: A contingent valuation experiment in South Korea

Global warming concerns have emphasized the need for carbon neutrality. Improving the efficiency of the electricity industry is one method of reducing CO2 emissions. There is a demand response policy that trades the saved electricity through voluntary adjustment of consumption patterns. The introduction of real-time pricing (RTP) based on advanced power supply systems is a method of transitioning to a demand-oriented power system. However, as Korea's power supply system is a relatively less efficient single-rate system, it is necessary to improve the efficiency of demand management. To transition to a demand-oriented power system in Korea, consumer preference is first investigated. This study evaluates the willingness to pay (WTP) for the introduction of RTP in Korea. Based on a survey of 500 households using the contingent valuation method, the monthly average WTP was found to be 2465 Korean won per household ($2.18 per household), which is approximately 7.8% of the electricity rate. Several additional factors influencing WTP were analyzed. Further analysis indicated that it is more effective to establish infrastructure for introducing RTP in local areas with low average electricity rates. These findings are beneficial for the development of future demand response policies.

The Need for Modeling the Impact of Behind-the-Meter Generation Trip on Primary Frequency Response Through Operational Experiences in Korea Power System

This letter introduces the impact of behind-the-meter generation (BTMG) trip on primary frequency response through recent operational experience in Korea, and examines whether this impact can be appropriately modeled in power system analysis. The most influential parameter for properly modeling BTMG trip is discussed in the case studies, demonstrating that simulation-based studies can reproduce the interesting observation of instantaneous load increase (i.e., the impact of BTMG trip). The outcome of this letter highlights the necessity for modeling BTMG trip in frequency stability analysis, especially for power systems with high penetration of BTMG.

BESS를 이용한 대규모 발전단지 제약완화 효과에 관한 연구

In case of 765kV transmission line tripping, there is a Special Protection Sheme(SPS) in Korea power system. To avoid generator over-speed, preselected generators can be tripped by SPS. However, the system frequency can be under the Under Frequency Relay(UFR) 1st pickup level 59.92Hz when large scale generators are tripped. Accordingly, generation constraints can arise until new transmission lines are installed. In this paper, we proposed BESS for mitigating generation constraints of large scale generators, and we applied to the Korean power system in 2022 to analyze the effects of BESS application.

Maximizing Distributed Energy Resource Hosting Capacity of Power System in South Korea Using Integrated Feeder, Distribution, and Transmission System

Intermittent power generated from renewable distributed energy resource (DER) can create voltage stability problems in the system during peak power production in the low demand period. Thus, the existing standard for operation and management of the distribution system limits the penetration level of the DER and the amount of load in a power system. In this standard, the hosting capacity of the DER is limited to each feeder at a level where the voltage problem does not occur. South Korea applied this standard, thereby making it hard to achieve its DER target. However, by analyzing the voltage stability of an integrated system, the hosting capacity of DER can be increased. Therefore, in this study, the maximum hosting capacity of DER is determined by analyzing an integrated transmission and distribution system. Moreover, the fast voltage stability index (FVSI) is used to verify the determined hosting capacity of DER. For this, the existing interconnection standard of DER at a feeder, distribution system, and transmission system level is investigated. Subsequently, a Monte Carlo simulation is performed to determine the maximum penetration of the DER at a feeder level, while varying the load according to the standard test system in South Korea. The actual load generation profile is used to simulate system conditions in order to determine the maximum DER hosting capacity.

Impacts of a Japan–South Korea power system interconnection on the competitiveness of electric power companies according to power exchange prices

In many regions, international power system interconnections provide economic, energy-security, environmental, and technical benefits. In contrast, such interconnections remain scarce in Northeast Asia. In 2016, after approving a joint memorandum of understanding between major electric power companies from China, Japan, South Korea, and Russia, related initiatives regained momentum in the region. Nevertheless, the corresponding developments in Japan remain limited, mainly owing to the lack of involvement of Japanese electric power companies. This study represents a pioneering attempt to provide an economic assessment based on power exchange prices of a power system interconnection between Japan and South Korea regarding the competitiveness of electric power companies in terms of competitive business segments and strategic consequences. We found that although the position of Japanese generators may slightly deteriorate, that of the supply segment would substantially improve, thus suggesting that more opportunities than threats are derived from the interconnection. This promising outcome may foster the adoption of an interconnection with South Korea considering the positive economic and business perspectives in Japan. Furthermore, realizing the interconnection may improve the energy security and air quality in the region.

Effects of the move towards renewables on the power system reliability and flexibility in South Korea

The plan to shift towards renewable energy has recently become the central part of the energy policy on the power system in South Korea. The sudden shift towards renewable energy has raised questions regarding the reliability and flexibility of the power system. This paper proposes a research framework to evaluate the new policy in South Korea from various aspects using three simulation models in a series. The first optimal generation model finds the optimal electricity generation mix and provides the total generation cost and environmental impact of the given long-term capacity expansion plan. The other two simulation models assess the reliability and flexibility of power systems, respectively. Within the research framework, we introduce a new probabilistic index to quantitatively measure the flexibility. The results of applying the framework into the new policy show that the policy fails to guarantee the target reliability level and increases costs and emissions. Achieving target system reliability will require additional capacity, and system flexibility is very sensitive to the type of capacity added. If the Korean government decides to add more capacity, natural gas turbine power plants turn out to be a good option from the point of economic, environmental, and flexibility considerations.

The Load Model Composition Method in Power Systems Using Artificial Neural Network

An accurate load model is necessary to improve the accuracy of power systems dynamic stability analysis. Recent studies to estimate accurate load model have mainly been focused on the measurement-based load modeling and the method to estimate a single representative load model called load model composition or load representation. The current load model used for the dynamic stability analysis in South Korea power system was aggregated with the measurement data from only three distribution stations. The proposed algorithm is the load model composition method based on artificial neural network technique using more measurement data than the algorithm to estimate the current load model. The proposed load model composition method using the artificial neural network uses the load composition ratio as the input value and the ZIP model parameter, which is the estimation result at each distribution line, as the output value. The measurement data to estimate the parameter were collected from 105 distribution lines of 9 substations. The performance of proposed algorithm was verified for three perspectives in the case studies. The accuracy of the proposed algorithm has been improved by comparing the measurement data with the calculated result by using the proposed model. The mean absolute percentage error (MAPE) between the measured data and the proposed model is 1.7%. The proposed algorithm could be applied to estimate the representative load model using data measured at multiple measurement points.

Improved Coordinated Control Strategy for Hybrid STATCOM Using Required Reactive Power Estimation Method

The penetration level of renewable energy resources has grown in such a way that their effects on the power system can no longer be neglected. In order to cope with these problems, grid operators are forced to improve the stability of the grid connection point, and the static synchronous compensator (STATCOM), which has a fast dynamic response is emerging as an alternative. Due to the prohibitive cost of STATCOM, however, grid operators have begun applying a new concept of hybrid STATCOM, which is a combination of mechanically switched capacitors (MSCs) and STATCOM. Thus, this paper investigates the use of new coordinated control between STATCOM and MSCs, and the solution relies on the required reactive power estimation method using online grid strength level (OGSL) index, which is newly proposed in this paper, and the optimal MSCs allocation algorithm. Following the proposed procedure, an improved coordinated control scheme is obtained whose objective is to reduce the switching times of the MSCs while maximizing the reserve reactive power margin of the STATCOM in transient state. This proposal is analyzed on the Jeju island power system in South Korea with the developed hybrid STATCOM model.

Performance Evaluation of BESS for Korean Power System Using Equivalent Power System Circuit Model

Abstract This paper describes a method of modeling power system elements involved in frequency-active power control using frequency data of south Korea power system. A particle swarm optimization method is used for estimating the parameters of the transfer function which illustrates the relationship between frequency and active power deviation. To obtain the optimal parameter estimation, we use the mean absolute percentage error (MAPE) index for evaluating the accuracy of estimation compared to real data. Real frequency and power data from KPX were used for comparison studies. From the proposed equivalent power system circuit model, we achieved 0.0052% MAPE compared to real data. To evaluate the BESS frequency regulation performance, we considered the BESS control algorithm which is based on the data of Korea electric power corporation (KEPCO). From this case study, we confirmed that the BESS which is operated in south Korea can improve frequency regulation in case of frequency event by increasing nadir frequency up to 0.0335Hz.

A study on alternative method of self – starting generator using ESS

ESS is widely used in FR power system in Korea. In this paper, we propose a method of starting the supply generator by energizing the transmission line to the ESS instead of the self-starting gener...

Governing the Atom: State, Society, and the Nuclear Power System in South Korea

Governing the Atom: State, Society, and the Nuclear Power System in South Korea

Transmission network expansion planning considering risk level assessment and scenario‐based risk level improvement

Renewable energy sources (RESs) are actively connected with the grid, and thus the requirement for transmission network expansion planning has increased. When RESs are added to the grid as independent power plants under a deregulated power system structure, an independent system operator managing the transmission system should evaluate the impact of RES penetration. The system operator should restrict the capacity of the RES to be installed or perform transmission network expansion planning if necessary. This study proposes risk assessment (RA) based on an exponential risk level (RL) model to evaluate the negative effects of RES penetration and introduces a method of applying RA in scenario-based transmission network expansion planning. The index of RL reduction via a scenario is formulated as an economic efficiency indicator for reducing the RL, based on the result of RA. A case study is performed on an actual power system in South Korea. For two cases based on the penetration of RESs, transmission network expansion planning considering the proposed RA is performed for several scenarios, and then, the best scenario for each case is selected.

A Study on Capacity Credit and ESS Evaluation for WTG and Multi-ESS in Power System

This paper proposes a new method for evaluating Effective Load Carrying Capability (ELCC) and Capacity Credit (CC) of a power system including Wind Turbine Generator (WTG) combined with Multi Energy Storage System (ESS). The WTG can only generate electrical power when the wind is available. Because of the fluctuation of wind speed, WTG generates intermittent power. In the reliability viewpoint of power system, the intermittent power of WTG is similar to the probabilistic characteristics based on the on-off power due to the mechanical availability of conventional generators. Therefore, high penetration of WTG will cause difficulties in power system operation. The high penetration of numerous and large capacity WTG can risk the power system adequacy, quality, and stability. This study develops a new method to assess how much the penetration of WTG can be extended when WTG is combined with ESS. This paper demonstrates various case studies of ELCC and CC of a power system containing WTG combined with Multi ESSs using a model system similar to Jeju island power system in Korea.

Dissimilarities of Physical Meaning between Loss of Load indices based on Load Curve Types

Abstract This paper proposes a conversion function and a method to transform LOLED (days/year) using daily peak load curve into LOLEH (hours/year) using hourly load curve and describes a relationship between LOLED and LOLEH. The indices cannot only be just transformed arithmetically but also have different characteristics physically because of using their different load curves. The conversion function is formulated as variables of capacity and a forced outage rate of generator, hourly load daily load factor, daily peak load yearly load factor and etc. Therefore, the conversion function (γ = φ(.)) is not simple. In this study, therefore, the function is formulated as linear times of separated two functions. One is an exponential formed conversion function of daily load factor and the other is a formulated with an exponential typed conversion function of daily peak load yearly load factor. Furthermore, this paper presents an algorithm and a flow chart for transforming LOLED into LOLEH. The proposed conversion function is applied to the actual KPS (Korea Power System) in 2015. The exponent coefficients of the conversion functions are assessed using the proposed method. Finally, assessment errors using the conversion function for case study of the actual system are evaluated to certify as a first proposed method.

두 종류의 부하곡선에 관한 공급지장시간기대치(LOLE)의 상호 변환관계성

This paper develops a conversion function and method transforming from daily peak load curve used LOLED [days/year] to hourly load curve used LOLEH[hours/year]and describes relationship between LOLED [days/year] and LOLEH [hours/year]. The indices can not only be transformed just arithmetically but also have different characteristics physically because of using their different load curves. The conversion function is formulated as variables of capacity and forced outage rate of generator, hourly load daily load factor and daily peak load yearly load factor, etc. Therefore, the conversion function (γ=φ(.)) cannot be simple. In this study, therefore, the function is formulated as linear times of separated two functions. One is an exponential formed conversion function of daily load factor. Another is formulated with an exponential typed conversion function of daily peak load yearly load factor. Futhermore, this paper presents algorithm and flow chart for transforming from LOLED[days/year] to LOLEH[hours/year]. The proposed conversion function is applied to sample system and actual KPS(Korea Power System) in 2015. The exponent coefficients of the conversion functions are assessed using proposed method. Finally, assessment errors using conversion function for case studies of sample system and actual system are evaluated to certify the firstly proposed method.

An Analysis of Energy Storage Systems for Primary Frequency Control of Power Systems in South Korea

Energy storage systems (ESSs) have a quick response and outstanding functions when used for frequency regulation. This paper examines the effect of an ESS used in conjunction with the primary frequency control (PFC) of a power system in South Korea. A simple low order system frequency response (SFR) model is used to undertake a simulation with MATLAB Simulink. The simulation includes gas, hydro and steam turbines and the ESS with the PFC. The results show that the ESS has a remarkable effect in the PFC and that it is more efficient in a weak grid. When more ESSs are added, the substitution effect is weaker according to the simulation results.

Multi-period energy planning model under uncertainty in market prices and demands of energy resources: A case study of Korea power system

This paper presents a mathematical framework for planning an energy supply system. The proposed model takes into account important factors affecting the total cost of supplying commercial energy such as market prices and waste disposal costs. Forecasting models are employed to predict future prices and demand levels. Given the renewable energy portfolio standard that promotes energy generation from renewable sources, a large-scale nonlinear planning problem is decomposed into a mixed integer linear program and a nonlinear program for traditional and renewable energy sectors, respectively. Nonlinearity arises from the learning curve that describes cost changes through future advances in technologies for exploiting renewable energy sources. The suggested approach can provide insights for crafting long-term policies, which can then be revised with updated information. The modeling framework is illustrated using public data from South Korea, interpreted in light of country's policies. Results based on various scenarios indicate that uncertainty and the cost of waste disposal facilities significantly affect the optimal policy choice.