Steady-state Voltage Stability Research Articles

A Steady-State Voltage Stability Analysis of Power Systems With High Penetrations of Wind

As wind generation begins to contribute significantly to power systems, the need arises to assess the impact of this new source of variable generation on the stability of the system. This work provides a detailed methodology to assess the impact of wind generation on the voltage stability of a power system. It will also demonstrate the value of using time-series ac power flow analysis techniques in assessing the behavior of a power system. Traditional methods are insufficient in describing the nature of wind for steady-state analyses, and as such, a new methodology is presented to address this issue. Using this methodology, this paper will show how the voltage stability margin of the power system can be increased through the proper implementation of voltage control strategies in wind turbines.

Simple and efficient method for steady-state voltage stability assessment of radial distribution systems

Abstract A new static voltage stability index of a radial distribution system is proposed to faithfully evaluate the severity of the loading situation, thereby predicting for voltage instability at definite load value. The proposed index includes different parameters which affect the steady-state voltage stability of distribution systems, therefore it gives accurate results. The maximum value of 1 of that index denotes the point where the system reaches the point of collapse whereas a minimum value of 0 shows the state of no load. The performance of the new index was tested on two radial distribution systems consisting of 33 and 85 buses. Comparison between the results of the new index and those of previous indices showed that the new index yielded reliable results in predicting voltage stability condition of the system. The new index overcomes the problem which faces many previous indices especially as the load approaches the critical point. Analysis of the two-bus equivalents of the test systems under different scenarios is also presented. A new P–Q plane of stability is introduced based on the equation of the proposed index. The active, reactive and apparent power margins are then directly determined from the voltage stability boundary.

A Novel SVC Allocation Method for Power System Voltage Stability Enhancement by Normal Forms of Diffeomorphism

Location of the static VAR compensator (SVC) and other types of shunt compensation devices is important for the enhancement of the voltage stability for practical power systems. With the theory of the normal forms of diffeomorphism, this paper proposes a new method to solve this problem. The proposed method makes use of the nonlinear participation factors, in which the nonlinearity of power systems can be taken into consideration. As a result, the most suitable location where the SVC should be used in power system can be determined, even for the cases in which the system is characterized with strong nonlinearity. In order to show the effectiveness of the proposed method, the New England 39-bus power system with SVC is used as an example. Calculation results show that with the SVC located at the place where the proposed method determined, the voltage stability is considerably enhanced. The steady-state voltage stability index and the time domain simulation results verify the effectiveness of the proposed method.

Voltage Stability Assessment of Multi-Machine Power Systems Using Energy Function and Neural Networks Techniques

Voltage stability problems have been one of the major concerns for electric utilities as a result of heavy loading of power system. Steady state voltage stability analysis is effectively used to determine a stability margin that shows how close the current operating point of a power system to the voltage collapse point. This article presents a generalized energy function for voltage stability assessment of multi-machine power systems. The formulated energy function provides an excellent indicator of the system vulnerability to voltage collapse. It is, also, used to rank the system buses according to their contributions to voltage collapse. The proposed technique is applied to a test system and Ontario-Hydro real power system. Also, an investigation on the application of artificial neural networks (ANN) in voltage stability assessment has been developed. A multi-layer feed-forward ANN with error back-propagation learning algorithm is proposed for calculation of voltage stability margins (VSM). Extensive testing of the proposed ANN-based approach indicates its validity for determination of power system voltage collapse.

DETERMINATION OF TRANSMISSION TRANSFER CAPABILITY WITH SECURITY AND VOLATAGE STABILITY

There has been an increased interest in quantifying the transmission transfer capability of power systems. Transfer capability indicates how much a particular bulk power transfer can be changed without compromising system security under a specific set of operating constraints and voltage stability capturing various contingencies. Hence this paper will touch on the security-constrained optimal power flow and P-V methodology for providing insight into the secure limit of interface flow between areas and steady-state voltage stability. An attempt to cover as much of the field as possible has been made by quoting tests on 2003 Korean electric power system.

Harmonics and voltage stability analysis in power systems including thyristor-controlled reactor

In this study, non-sinusoidal quantities and voltage stability, both known as power quality criteria, are examined together in detail. The widespread use of power electronics elements cause the existence of significant non-sinusoidal quantities in the system. These non-sinusoidal quantities can create serious harmonic distortions in transmission and distribution systems. In this paper, harmonic generation of a static VAR compensator with thyristor-controlled reactor and effects of the harmonics on steady-state voltage stability are examined for various operational conditions.

전압 안정도 제약계통에 대한 고온초전도 케이블 적용효과

본 논문은 전력계통의 전압 안정도 제약 문제를 해결하는데 고온 초전도 케이블을 적용하기 위한 기법을 제시하였다. 대전력계통의 유효 송전용량은 종종 전압 안정도 제약에 의해 결정된다. 기존의 초전도 케이블 응용 연구는 주로 도심지역의 고밀도 전력 수송 문제를 해결하는 대안으로 연구의 초점을 두어왔지만, 고온 초전도 케이블의 선로정수 개선효과를 이용하면 전압 안정도로 제약된 계통의 송전용량을 증가시킬 수 있어 그 응용 범위가 확대될 수 있다. 전압 안정도에 의한 최대 수송전력을 결정하는 데는 IPLAN에 의한 P-V곡선을 이용하였고, 대체 대상선로는 부하 증가시 무효전력 손실감도가 가장 큰 선로로 하였다. 결과의 타당성을 검증하기 위해 IEEE 14모선 계통을 사용하였으며, 적용결과 Case Ⅱ는 70[%], Case Ⅲ에서는 160[%]의 추가 수송 능력 증가를 가져올 수 있었다.

Voltage stability analysis in the power systems including non-linear loads

Recently, the number of non-linear elements connected to power systems and the non-sinusoidal quantities caused by non-linear loads have been increasing. The influences of the non-sinusoidal quantities on the steady-state voltage stability of power systems have been neglected so far. In this study, a new algorithm presents the effects of the harmonic components caused by non-sinusoidal quantities on voltage stability that are a synthesis of the harmonic power algorithm and the conventional voltage stability analysis. According to this algorithm, the stability analysis was carried out as a numerical application for two different loading conditions in the 11-bus electrical power system. In the first case, the system consists of only linear loads, and in the second case it consists of linear and non-linear loads. Finally, the comparison of harmonic power flow based on voltage stability analysis and conventional voltage stability analysis is examined for the above cases.

03/02298 Co-ordinated application of FACTS devices to enhance steady-state voltage stability: Messina, A. et al. International Journal of Electrical Power & Energy Systems, 2003, 25, (4), 259–267

03/02298 Co-ordinated application of FACTS devices to enhance steady-state voltage stability: Messina, A. et al. International Journal of Electrical Power & Energy Systems, 2003, 25, (4), 259–267

Co-ordinated application of FACTS devices to enhance steady-state voltage stability

This paper examines the co-ordinated application of flexible ac transmission system (FACTS) technologies to extend system voltage stability margins. A systematic analysis and design method, based on the singular value/eigenvalue decomposition analysis of the load-flow Jacobian and the study of the controllability characteristics of an equivalent state model is used to study the voltage instability phenomenon as well as to assess the potential for small-signal voltage stability improvement by means of FACTS compensation. The method is of particular interest for the preliminary design of new system devices and the study of interactions among existing controllers. Results obtained using a practical system representative of the Central American interconnected network are presented, illustrating the application of FACTS technologies to extend voltage stability limit.

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.

A novel fuzzy index for steady state voltage stability analysis and identification of critical busbars

Abstract In this paper, a novel fuzzy index is proposed for the prediction of steady state voltage stability conditions in transmission networks. The uncertainties in the input parameters are efficiently modeled in terms of fuzzy sets by assigning trapezoidal and triangular membership functions. The results include fuzzy load flow solutions for the base case and critical conditions with and without contingencies. The proposed fuzzy voltage stability index clearly indicates the location and status of critical busbars. Case studies have been conducted on standard test systems (IEEE 14-bus, 30-bus, and 57-bus) with proper validation of the results.

Determination of Steady-State Voltage Stability Limit Using P-Q Curve

P -V and Q - V curves are commonly used to determine the steady state voltage stability limit of a power system. In this letter, a new method of determining the voltage stability limit using the P -Q curve is presented. The boundary of the voltage stability region is first determined and then presented in the P -Q plane. For a given operating point, the voltage stability margin can easily be determined from the stability boundary in the P -Q plane. The proposed method of determining the voltage stability limit was tested on a simple system and very interesting results were found.

Determination of interface flow margin using the modified continuation power flow in voltage stability analysis

A new concept of interface flow margin in terms of steady-state voltage stability is introduced. The interface flow margin is the active power flow margin of the key transmission lines between one region and others under a fixed load demand condition. In addition, a technique is proposed to trace interface flow-voltage (f-V) curves by applying a continuation method. From the f-V curves, the interface flow margin can be easily obtained, which is useful to determine the secure flow limit of the specified interface. In the case study, an illustrative example with the New England 39-bus system is shown.

Reactive Security Study of a Large Power System

This paper presents results of a reactive security study of the New South Wales main grid. System modeling is focused on the effect of load dynamics. A composite dynamic load model is used. The reactive security study reported here is based on a steady-state approach. A general method for steady-state voltage stability analysis is used to compute the saddle-node bifurcation point and the relevant security margin. The reactive security in the studied area is evaluated for the system under various scenarios. The impact of load models on the security margin is studied in detail.

Corrective Schemes for Voltage Stability Using Two Different Indicators

This paper discusses the steady state voltage stability analysis of two power systems: Wale and Hale 6-bus system and the IEEE 30-bus system by using four different correction schemes: transmission path, reactive compensation, generation voltage and reactive path, and load shedding. These correction schemes can improve voltage stability with the help of two indicator techniques: L-index value and V-Q sensitivity value. Results of tests carried on the above-mentioned systems are provided and discussed.

Steady state voltage instability assessment in a power system

With the increase of loading and exploitation of power transmission system and also due to the improved optimized operation, the problem of voltage stability and voltage collapse attracts more and more attention. The phenomenon of possible steady state voltage instability is creating serious concern among operators of large interconnected power systems. Maintaining adequate system voltage has become a major problem, as utilities are being forced to operate the system close to the thermal capability or steady state voltage stability limit. A voltage collapse can take place in power systems or subsystems quite abruptly, which requires improved continuous monitoring of the system state. There are different methods used to study the voltage collapse phenomenon, such as the Jacobian method, the simplified Jacobian method, the multiple load flow method and the voltage collapse proximity indicator method. It is proposed to modify the method of multiple load flow to obtain the weakest buses and the maximum injected powers for each bus. The method of voltage collapse proximity indicators is also simplified. These different methods are applied on a simple power system to study the problem of voltage collapse, and a comparison is made between them with indicating the merits and demerits of each.

Fuzzy-expert system for voltage stability monitoring and control

This paper presents a fuzzy-expert system approach to steady-state voltage stability monitoring and control in a power system. In the proposed rule-based expert system, a systematic procedure for voltage stability monitoring and control is developed. Key elements associated with voltage instability are identified using modal analysis. The information from the above analysis is stored in a knowledge base. A set of decision rules relating key system variables to voltage stability are established. The designed expert system performs voltage stability monitoring and control through deductive reasoning. The New England 39-bus system is taken as a case study to illustrate the proposed procedure.

Series capacitors combined with static VAR compensators for enhancement of steady-state voltage stabilities

Use of series capacitors (SC) alone or in combination with static VAR compensators (SVC) for enhancement of steady state voltage stability are illustrated. The appropriate compensation percentage is obtained from the steady-state voltage stability point of view. The influence of a combination of SC and SVC on ratings and performance are studied. Limitations of the use of series capacitors alone are examined.