Voltage Collapse

Electricity interruption gives rise to a complete disorder in the society and is therefore unappreciated and highly criticized. Consequently, it becomes a great concern for national and/or private energy companies to conduct their power systems under severe requirements. These companies are asked to ovoid failures that induce power oscillation, voltage drop and high frequency deviations because these phenomena can produce the loss of the system integrity by rapid voltage collapse or any transient stability mechanism. New technology alternatives such as FACTS (flexible alternative current transport systems) can positively support conventional control systems such as PSSs (power system stabilizer), AVRs (automatic voltage regulator) and TGs (turbine governor). But at the same time, it is to recognize that power system control becomes more complicate and requires suitable global strategies. The paper deals with this problem and aims to show that UPFC is a suitable device in particular ...

Every transmission system has voltage stability limit which may lead to voltage collapse if an undetected bulk transmission network is operated close to its operating limit. This research work uses continuation power flow method to identify voltage collapse point for Bangladesh Power System Network (BPSN). For the identification of weak buses, an analytical based technique of tangent factor has been presented. The risk of voltage collapse has been mitigated by placing SVCs at the weak buses of the system using load flow analysis. Moreover, sensitivity based approach has been introduced to determine optimal location of Static VAR Compensator (SVC) for the voltage security enhancement. A comparative analysis has been documented considering the size of reactive power to improve the loading factor of the overall network at the end of this work.

ABSTRACT Reactive power management is an important issue especially in deregulated environment. It will be more crucial when power systems are heavily loaded and voltage collapse may occur. In this paper the objective is to assess the effects of each contingency on reactive power margin in order to rank the contingencies. In order to maintain security of power system in certain level, the impact of each contingency on power system should be estimated. This paper uses the WSCC VSC and base on that it defines a new index with less computational effort. The proposed method is successfully applied to the modified IEEE 39-bus system where significant results are attained.

The  global  economic  recession  has  contributed  in  o  small  measure,  in  the
increasing  number of blackouts throughout the  world as  a result of voltage instability and collapse.  The environmental consideration has  also contributed  by arresting  the commission of  new  power  stations  and  transmission  lines,  thus  resulting  in  overload  of  the  existing system.  This  calls  for  a  change  to  a  new  direction  by  using  the  power  system  tool -box  in MATLAB to stem down the tide. The results showed  a  balanced system, as confirmed by  asubstantial flat voltage profiles at all levels during transmission.

The Western Region of the Entergy System is limited in both generation and transmission. Steady state and dynamic voltage stability analysis has indicated that the region can be subjected to severe voltage instability followed with possible voltage collapse under certain critical double contingencies. In order to prevent voltage collapse in the region, Entergy developed a fast acting load shedding scheme called VSHED. This scheme utilizes the existing supervisory control and data acquisition (SCADA) system to perform load shedding without manual intervention. This paper discusses the results of the voltage stability analysis performed to analyze the problem, the design and development of the VSHED scheme, computer implementation and a disturbance during which the VSHED scheme operated successfully and saved the Western Region of the Entergy System

Voltage control and voltage stability problems are not new in the operation of electric power networks but are now receiving special attention in many countries because of a greater need for improving efficiency of usage of transmission capacity in the competitive electric energy market. Practically, the idea of P-V and Q-V curves is used to determine the maximal reactive margin

Abstract:
Investigation and online monitoring of power system stability have become vital factors to electric utility suppliers. At present power system utilities operate very close to the limit of system stability owing to an increasing number of new economic and environmental restrictions. Researchers have been trying to find out the most effective way for online system status monitoring, so that necessary precautions can be taken prior to voltage collapse. Several methods have been proposed for analysing voltage collapse phenomena. An effective method for online system status monitoring and thus voltage collapse prediction is described. The basic methodology implied in this technique is the investigation of each line of the system through calculating line stability indices. The proposed method was tested on the IEEE 24-bus reliability test system and has been found to be accurate and precise in voltage collapse prediction. A comparative study with other methods has also been carried out indicating that the proposed method has some advantages over the others.

Modern power systems are operating closer to their limits, due to load growth and maximum efficiency of usage of transmission line capacity. Operation of power system under such condition may endangers the voltage stability of network and leads to voltage collapse. Voltage stability indices are used as an efficient, accurate and uncomplicated method in static voltage stability analysis. In this paper a review of most common line voltage stability indices which previously studied in literature, is provided. A model of IEEE-14 Bus System has been presented as case study. The simulation tool used was DIgSILENT PowerFactory and the indices were computed using the DPL. Simulation results approved the theoretical background of indices.

The declining reliability of the US electric power system is raising major concerns amongst both politicians and power engineers in the USA. One of the reasons put forward by the North Electric Reliability Council (NERC) is the detrimental role played by the protection systems during large disturbances, which tend to help the perturbations to propagate through over-tripping of fault free system components due to hidden failures. It turns out that the present practice in power transmission planning and online security analysis is to neglect the impact of the protection systems. In addition, the aim is to mitigate the vulnerability of the system to the loss of a single piece of equipment only by carrying out an N-1 security analysis. Consequently, the risk of cascading failures leading to blackouts and brownouts is neither assessed nor managed. This paper describes methodologies together with algorithms that assess the conditional risk of catastrophic failures in electric power networ...

The tendency towards maximizing economic benefits has led power systems utilities to run close to the limits of stable operation. This has necessitated the study of the stressed situation of the power system network to accomplish efficient energy management without losing its reliability. On-line monitoring of power system stability has become a vital factor for electric utilities. An effective method for real-time monitoring of system status and thus voltage collapse prediction is described. The proposed technique investigates each line of the system through calculating an indicator that varies from 0 (no load condition) to 1 (maximum permissible loading condition). The basic concept of maximum power transfer through a line is utilized. The proposed contingency evaluation technique is applied on the IEEE 24 bus and IEEE 6 bus reliability test system and is found to be accurate in assessing the stressful status of the lines.

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 ...

In this paper, an approach for optimal allocation of flexible AC transmission system (FACTS) devices under deregulated power systems is presented. The approach considers system operation under normal and contingency states along with their related probabilities to occur. For each state, FACTS devices are optimally utilized to minimize operating cost. If a contingency occurs, preventive/corrective control strategy is applied to prevent voltage collapse as well as to relieve transmission congestion. During corrective control, fast control action is utilized while during preventive control, both fast and slow control actions are employed. The objective of normal state is to maximize social welfare while the objectives of contingency states are to maximize social welfare and to minimize compensations paid for generations re-scheduling and load shedding. The overall problem is formulated as a mixed integer nonlinear programming problem and is solved using hybrid Particle Swarm Optimization. The effectiveness of the proposed approach is demonstrated on modified IEEE 14 bus test system.

Faced with the need of achieving the highest possible efficiency in the utilization of primary resources, nuclear power plants (NPPs) are considered as a viable alternative or addition. In case of transmission system voltage interruption, especially low voltage, NPPs have historically been susceptible to stations trip. Because of low voltage problem, the resulting loss in real and reactive power support can embitter transmission events. In this paper, the possibility of low bus voltage in the Western grid of the Bangladesh power system network, where the planned Rooppur NPP will be sited, is calculated and reported. It has been observed that even with small load factor, buses around the Rooppur NPP experience low voltage. A detailed investigation to study the problem and possible solutions is thus recommended.

... In the simple case of Figure 1, the VIP based device is placed at a radial point in the network topology. This ap-plication is useful when there is a clear distinction be-tween the “sink” and the “source”, such as the upstream and downstream sides of a distribution station. ...

SUMMARY This paper reports the initial phase of an Information Technology (IT) initiative to improve the utilisation of the Norwegian power grid. We adopt a scalable approach, beginning with a focus on the use of local intelligence ("agent"), and gradually integrating these agents into the existing IT infrastructure. In particular, the paper reports on the implementation and testing of two new applications. These are the Voltage Instability Predictor for on-line tracking of distance to voltage collapse, which is primarily a local device, and a Secondary Voltage Regulation scheme for coordinated control of SVCs and synchronous condensers, which is presently a control centre application.

In this paper, a detailed analysis of the use of optimization techniques in the study of voltage stability problems, leading to the incorporation of voltage stability criteria in traditional Optimal Power Flow (OPF) formulations is presented. Optimal power flow problems are highly nonlinear programming problems that are used to find the optimal control settings in electrical power systems. The relationship

A smart relay scheme for long term voltage in- stability phenomena is proposed. The method, called VIP++ is based on local area measurements and seeks to improve observability and robustness of a previously proposed Volt- age Instability Predictor (VIP) (4) using measurements only from the bus where the relay is placed. Several strategies can be adopted to deal with the