Total Transfer Capability Research Articles

炭素繊維強化積層複合材の細径ピンによる穿孔と細径ボルトの密集配置による接合

In this paper, a mechanical joint that consists of densely arranged thin bolts is proposed for joining CFRP laminates. Tiny bolts have only low load transfer capacity, but their dense assemblage can provide the same total load transfer capability as a smaller number of large bolts. Bolt holes are opened by piercing sharp pointed pins in a B-stage prepreg and the inserted pins are replaced with release coated tubes, which are kept inserted during the prepreg cure. At the completion of cure, removing the tubes, smooth bolt holes are formed in the CFRP laminate. Ultrasonic vibration assisted pin insertion test was also conducted, leading to a drastic reduction of the required insertion force, but it did not reduce the fiber breakage in the pierced hole. An experimental study was also done to explore the effects of the bolt size and the hole forming method i.e., drilling and piercing, on the joint strength. Finally, a series of tensile shear tests of the proposed joints under both quasi-static and low-cycle fatigue loading conditions was carried out to investigate their possibility and feasibility.

Total supply capability and its extended indices for distribution systems: definition, model calculation and applications

This study systematically proposes and defines a set of new quantitative indices named total supply capability (TSC) and its associated indices, such as available supply capability, substation supply capability, network transfer capability, maximum supply capability and expandable supply capability. The concepts in the TSC family provide new approaches to analyse and optimise distribution networks. TSC for distribution systems is comparable to the total transfer capability for transmission systems, but there are significant differences, such as the radial configuration and service restoration in TSC consideration. TSC is defined as the maximum load to serve under the expanded N−1 security guideline for the distribution system, taking into account the capacities of the substation transformers, network topology, link capacity and other constraints. Here, the expanded N−1 security means a successful, near-immediate service restoration to all loads except for the faulted section. A mathematical model for TSC is then set up and an accurate method is presented to calculate the TSC with lingo. Sample applications are provided to illustrate a new TSC-based approach to evaluate the link capacity and obtain the reconductoring proposal. The results from a real distribution system demonstrate the effectiveness of the proposed TSC modelling and TSC-based approach.

Differential evolution based method for total transfer capability evaluation

The application of Differential Evolution (DE) to compute the Total Transfer Capability (TTC) in deregulated market is proposed in this paper. The objective is to maximize a specific point-to-point power transaction without violating system constraints using DE. This algorithm is based on full ac optimal power flow solution to account for the effects of active and reactive power flow, voltage limits, and line flow limits. The real power output of generators in source area and the real power of the loads in the sink area were adjusted to obtain the maximum transfer capability. In order to calculate TTC more accurately, Transmission Reliability Margin is incorporated in the calculation of TTC by considering single and multiline outages and also a three phase to ground fault near a bus and clearing it by isolating the faulty line after certain time interval. The performance of the proposed method is tested on the modified IEEE-30 bus system and results are compared with that of Particle Swarm Optimization method (PSO). Further, the results are compared with other published results using CPF and EP. It is found that DE provides more reliable results than other methods. Keywords: Total transfer capability, available transfer capability, transmission reliability margin, differential evolution, particle swarm optimization.

Formulation, computation and improvement of steady state security margins in power systems. Part II: Results

A steady state security margin for a particular operating point can be defined as the distance from this initial point to the secure operating limits of the system. Four of the most used steady state security margins are the power flow feasibility margin, the contingency feasibility margin, the load margin to voltage collapse, and the total transfer capability between system areas. This is the second part of a two part paper. Part I has proposed a novel framework of a general model able to formulate, compute and improve any steady state security margin. In Part II the performance of the general model is validated by solving a variety of practical situations in modern real power systems. Actual examples of the Spanish power system will be used for this purpose. The same computation and improvement algorithms outlined in Part I have been applied for the four security margins considered in the study, outlining the convenience of defining a general framework valid for the four of them. The general model is used here in Part II to compute and improve: (a) the power flow feasibility margin (assessing the influence of the reactive power generation limits in the Spanish power system), (b) the contingency feasibility margin (assessing the influence of transmission and generation capacity in maintaining a correct voltage profile), (c) the load margin to voltage collapse (assessing the location and quantity of loads that must be shed in order to be far away from voltage collapse) and (d) the total transfer capability (assessing the export import pattern of electric power between different areas of the Spanish system).

Formulation, computation and improvement of steady state security margins in power systems. Part I: Theoretical framework

A steady state security margin for a particular operational point can be defined as the distance from this initial point to the secure operational limits of the system. Four of the most used steady state security margins are the power flow feasibility margin, the contingency feasibility margin, the load margin to voltage collapse, and the total transfer capability between system areas. A comprehensive literature survey has shown that these security margins have been studied separately. This fact has suggested to the authors the possibility of researching a common analysis framework valid for all of them. This is the first part of a two-part paper. In part I, a novel mathematical formulation valid to address the study of any steady state security margin is proposed. The developed general approach is presented in three steps: (a) formulation, (b) computation, and (c) improvement of security margins. In part II, the performance of the proposed approach when used to compute and improve the aforementioned steady security margins is illustrated through its application to the Spanish power system. Results denote that this approach can be a useful tool to solve a variety of practical situations in modern real power systems.

Total transfer capability computation using small signal stability-based security constrained optimal power flow

In an open transmission access environment, the system operating conditions tend to be pushed close to the stability limits. Small signal stability, commonly in the form of low frequency oscillations, is considered to be a crucial factor since it limits the amount of power transfer through interconnected transmission lines under severe disturbances. This paper presents a novel approach to the assessment of the total transfer capability (TTC) using small signal stability-based security constrained optimal power flow (SSS-SCOPF), thereby enhancing small signal sense under a set of credible contingencies while maximizing power transfer. The eigenvalue perturbation method is used to derive the small signal stability constraint included in SSS-SCOPF, which is a linear inequality expressed in terms of the control parameters. In order to reduce the computational burden, Bender's decomposition method is applied to partition the TTC problem with the small signal stability constraint into an iterative two-stage mathematical programming problem. It is then solved by the primal-dual interior point method (PDIPM) in a master-sub problem iteration manner until no constraint violation occurs for each contingency. The effectiveness of the proposed method is clearly validated by comparison with the conventional optimal power flow (OPF) and SCOPF under the same array of transactions, base case, and line outages for the New England 39-bus system. Copyright © 2010 John Wiley & Sons, Ltd. This article was published online on 25 August 2010. Errors were subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected [20 September, 2010; 25 March, 2011].

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.

Evaluation and Improvement of Total Transfer Capability in an Interconnected Power System

With deregulation, the total transfer capability (TTC) calculation, which is the basis for evaluating available transfer capability (ATC), has become very significant. Total transfer capability (TTC) is an important index in power markets with large volume of interarea power exchanges and wheeling transactions taking place on hourly basis. Its computation helps to achieve a viable technical and commercial transmission operation. The aim of the paper is to evaluate TTC in the interconnections and also to improve it using reactive optimization technique and unified power flow controller (UPFC) device. TTC computation is carried out considering normal and contingency conditions such as single line, tie line and generator outages. Base and optimized results are presented, and the results show how reactive optimization and UPFC help to improve the system conditions and tie flows. Repeated power flow method is used for transfer capability computation due to its ease of implementation. A case study is carried out on a 72-bus equivalent system, which is a real-life system, a part of Indian Southern grid. The developed procedure is successfully applied to the three-area 72-bus system. Parameters like voltage magnitude, L-index, minimum singular value and MW losses are computed to analyze the system performance.

전체송전용량 향상을 위한 STATCOM 설비의 적용 위치 선정 및 과도안정도를 고려한 전체송전용량 분석

송변전설비들이 점점 중부하로 운용되어짐에 따라 송전용량이 전력회사에서 중요한 문제로 부각되어왔다. 한전 시스템의 경우 전체송전용량은 주로 전압 안정도에 의해 제한을 받고 있으며, 이의 향상을 위한 연구들이 계속하여 수행되어 오고 있다.BR 본 논문에서는 전압안정도 관점에서의 전체송전용량을 향상시키기 위하여 STATCOM 설비를 설치하는 위치를 효과적으로 선택하기 위한 송전용량지수가 제시된다. 이 지수를 소규모 전력시스템인 IEEE 39 모선 시스템에 적용하여 제시된 지수의 효과를 보여준다. 그리고, 이 소규모 시스템을 활용하여 부하가 증가할 때 전체송전용량에 전압안정도뿐 만이 아니라 과도안정도가 미치는 영향을 분석한다.

Rapid evaluation method for power supply capability of urban distribution system based on N − 1 contingency analysis of main-transformers

A proper evaluation on the power supply capability of urban distribution system is of much social and economical significance. In competitive marketing environment, to satisfy the sustainable growth of distribution loads, electric utilities must judge whether the return of power supply capability is sustainable and valued against the certain amount of investment. Therefore, to make up the insufficiency of traditional methods referring from the concept of total transfer capability (TTC) of transmission system, this paper proposes a straightforward method to evaluate the power supply capability (PSC) of distribution system, which is based on N − 1 contingency analysis of interconnected main-transformers. Firstly, a series of interconnected main-transformer groups are drawn from the main-transformers’ interconnection analysis after the topological simplification of distribution system. Secondly, the maximum average loadability of each main-transformer is concluded through the N − 1 contingency analysis of every interconnected group. Finally, based on a comprehensive analysis of all the interconnected groups’ results, the maximum permissible loadability of each main-transformer can be obtained, thus the PSC of the entire distribution system can be calculated. Through the application in a distribution system of Shanghai, China, the effectiveness and the accuracy of the method are demonstrated. The application results suggest that, the method presented in this paper is a simple and practical tool to evaluate the PSC of a distribution system, which needs only one calculation with constraints according to the N − 1 guideline. Moreover, the interconnection weak-points and the interconnection bottlenecks of the distribution system can be identified easily with this approach, thus providing effective references for urban distribution network planning and the following project investment decisions.

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.

Total Transfer Capability Assessment Incorporating Corrective Controls for Transient Stability using TSCOPF

Advancements have been made towards inclusion of both static and dynamic security into transfer capability calculation. However, to the authors' knowledge, work on considering corrective controls into the calculation has not been reported yet. Therefore, we propose a Total Transfer Capability (TTC) assessment considering transient stability corrective controls. The method is based on the Newton interior point method for nonlinear programming and transfer capability is approached as a maximization of power transfer with both static and transient stability constraints are incorporated into our Transient Stability Constrained Optimal Power Flow (TSCOPF) formulation. An interconnected power system is simulated to be subjected to a severe unbalanced 3-phase 4-line to ground fault and following the fault, generator and load are shed in a pre-defined sequence to mimic actual corrective controls. In a deregulated electricity market, both generator companies and large load customers are encouraged to actively participate in maintaining power system stability as corrective controls upon agreement of compensation for being shed following a disturbance. Implementation of this proposal on the actual power system operation should be carried out through combining it with the existing transient stabilization controller system. Utilization of these corrective controls results in increasing TTC as suggested in our numerical simulation. As Lagrange multipliers can also describe sensitivity of both inequality and equality constraints to the objective function, then selection of which generator or load to be shed can be carried out on the basis of values of Lagrange multipliers of its respective generator's rotor angle stability and active power balance equation. Hence, the proposal in this paper can be utilized by system operator to assess the maximum TTC for specific loads and network conditions.

モーリレー不要動作による事故波及の回避を考慮した電圧・熱容量TTC算出法の提案

This paper proposes a new computation method for Total Transfer Capability (TTC) with respect to thermal and voltage magnitude limits. TTC is formulated as an optimization problem and solved by The Primal-Dual Interior Point Method (PDIPM). In stressed power system, mho relays are possible factors for causing cascading failures because of their unnecessary operations caused by decrease in voltages in heavy load conditions. Therefore, in order to consider mho relay characteristics, the relay operating conditions are taken into account in the optimization problem as constraints to compute TTC. The effectiveness of the proposed method is demonstrated through IEEE 57 bus system model.

A probabilistic modeling based approach for Total Transfer Capability enhancement using FACTS devices

Available Transfer Capability (ATC) is a key concept in the restructuring of power systems. ATC is used by system operators to determine the ability of transmission system to transfer power and by system planners to indicate a system’s strength. ATC calculation involves determination of Total Transfer Capability (TTC) and two margins, Transmission Reliability Margin (TRM) and Capacity Benefit Margin (CBM). In fact, if the values of TRM and CBM are assumed to be constant, ATC is directly expressed by TTC. Therefore, improvement of TTC is an important topic in the current deregulation environments. Due to the uncertainty of power system behavior, the events such as transmission line outage can cause the transfer capability to decrease. Accordingly, transmission capability analysis needs a statistical forecast for an expected range of transfer capability. Thus, it is necessary to study TTC problem from a probabilistic point of view and consider the probabilistic feature of the power systems and the related contingencies.

Erratum: Total transfer capability calculation taking into consideration system uncertainties

In a liberalized power industry, key information used to determine how much can be transferred through the network is known as total transfer capability (TTC). Without considering the uncertain nature of power systems, we would be even skeptical whether TTC is actually meaningful in practice. This paper primarily purports to determine TTC based on the fuzzy set theory for continuation power flow (CPF), thereby capturing uncertainty. Given that uncertainties in the TTC calculation are estimated or measured, major uncertainty parameters affecting the TTC are replaced by fuzzy variables subject to their probability distributions in a fuzzy model. The purpose of this paper is to embark upon main features of the fuzzy continuation power flow (FCPF) algorithm that may effectively deal with uncertainties of load parameters and bus injections as well. For more realistic fuzzy modeling, the correlation algorithm is developed by integrating a correction phase into the FCPF results, aiming at reducing the range of the membership functions if there is accompanying information. Exposure and robustness indices based on risk analysis concepts are defined in this analytical framework. As such, the robust solution will assist in providing additional information on the actual ability of the network to a system operator. In other respects, it poses a significant influence on the potential curtailment of power trades from which the reinforcement strategy can be made by the system operator. The viability of the proposed method would be verified through a stark contrast with those obtained from the conventional CPF and the fuzzy power flow (FPF) in the IEEE-118 bus system. Copyright © 2008 John Wiley & Sons, Ltd.

A Study on the Effect of Generation Shedding to Total Transfer Capability by Means of Transient Stability Constrained Optimal Power Flow

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In nowadays deregulated market, total transfer capability (TTC) calculation, which is the basis for evaluating available transfer capability (ATC), has been becoming more significant. During the last decade, transient stability constraints have been included in the optimal power flow approach to maximize TTC. However, no previous work on investigating the effect of generation shedding action to TTC has been reported. Therefore, in this paper, we propose a TTC maximization by means of transient stability constrained optimal power flow considering the generation shedding action. Proper selection of the generator to shed is based on its Lagrange multiplier value of transient stability constraint. Our simulation results show how TTC can be increased to anticipate possible generation shedding. </para>

Investigation of Impact of Renewable Energy Penetration on System Total Transfer Capability at Risk

Total Transfer Capability (TTC) was defined to provide information for energy trading management and transmission system planning in a deregulated environment. Although TTC calculation has been well researched and conducted, a new method is still required to take into account the presence of generation from renewable energy sources. Among the renewable energy sources used nowadays, wind and solar energies have received the most attention. The increasingly widespread use of wind and solar power generation is expected to have an impact on the TTC due to the fluctuating output strongly depending on the wind speed and climate. This paper primarily investigates such impact on the system TTC. The uncertainty from wind and solar power generation outputs is integrated into the calculation by using the Monte Carlo simulation. Based on the risk concept, the TTC at risk is selected. The validity of the proposed method is illustrated through the numerical simulation conducted on the modified IEEE 30-bus test system.

Optimal placement of multi-type FACTS devices to enhance Total Transfer Capability using Improved Evolutionary Programming

An Improved Evolutionary Programming (IEP) is proposed to determine the optimal placement of multi-type Flexible AC Transmission Systems (FACTS) devices for maximising Total Transfer Capability (TTC) of power transactions. IEP simultaneously searches for types, locations, and parameters of FACTS devices, real power generations in source area, real power loads in sink area, and generation bus voltages to evaluate the feasible TTC value within power system constraints and FACTS devices operating limits. Test results on the modified IEEE 30- and 118-bus systems indicate that optimally placed optimal power flow (OPF) with FACTS by IEP could enhance TTC value far more than OPF without FACTS.

Application of Interval Arithmetic in the Evaluation of Transfer Capabilities by Considering the Sources of Uncertainty

Total transfer capability (TTC) is an important index in a power system with large volume of inter-area power exchanges. This paper proposes a novel technique to determine the TTC and its confidence intervals in the system by considering the uncertainties in the load and line parameters. The optimal power flow (OPF) method is used to obtain the TTC. Variations in the load and line parameters are incorporated using the interval arithmetic (IA) method. The IEEE 30 bus test system is used to illustrate the proposed methodology. Various uncertainties in the line, load and both line and load are incorporated in the evaluation of total transfer capability. From the results, it is observed that the solutions obtained through the proposed method provide much wider information in terms of closed interval form which is more useful in ensuring secured operation of the interconnected system in the presence of uncertainties in load and line parameters.

A New Evaluation Method of Available Transfer Capability of Tie Lines between Control Areas Considering Power Supply Reliability Margins

In a deregulated environment, fairness and transparency to power system operation are required and it is necessary to give information on the appropriate transmission capability to transmission network users. In this paper, a novel evaluation method of available transfer capability, total transfer capability and power supply reliability margins, based on Monte Carlo Simulation considering system uncertainties, is presented. IEEJ WEST 10-machine system model is utilized to examine the effectiveness of the proposed method. The simulation result shows that the margins play a significant role in the determination of the ATC.