Static Voltage Instability Research Articles

Influence of Geomagnetic Storms on Power System Static Voltage Security

The adverse effects of geomagnetic storms on power systems have been confirmed by numerous examples and observations. However, there remains a dearth of research on the quantitative assessment of the safety risks of a system under extreme geomagnetic storm conditions. Accordingly, in this study, we developed a risk assessment model for magnetic storm disasters based on the static voltage security region theory from the global perspective of power grid security. First, we determined the boundary shape of the static security region of a system under magnetic storm conditions and analyzed its influence on the voltage stability of the system from a regional perspective. Subsequently, a static safe-distance index was proposed to characterize the influence of a magnetic storm disaster on the system voltage. Considering the uncertainty in the injected power during a magnetic storm, we calculated the static voltage instability probability of the system. Through probability index analysis, a probabilistic safety assessment of the system under magnetic storm conditions was performed, and its overall static voltage safety level was measured. Finally, a simulation analysis based on the UIUC 150 node showed the proposed method to be reasonable and effective.

Characterization of static voltage stability region of offshore wind farms considering submarine cable capacitance parameters and converter saturation

Accurately characterizing the static voltage stability region (SVSR) is the key to ensure the safe and stable operation of offshore wind farms (OWFs). However, the traditional SVSR evaluation methods ignore the influence of capacitance parameters, and the stability criteria fail after d-axis current saturation, leading to a large deviation in the evaluation results. Therefore, this paper proposes an improved method to characterize the SVSR of OWFs, which takes the cable capacitance parameters and the saturation effect of the converter into account. Firstly, based on the equivalent circuit method, the power common connection (PCC) voltage charact- erization model considering cable capacitance parameters was derived. Then, the DC voltage stability was defined to describe the static voltage instability caused by the current limiting of the converter. The SVSR constraints are summarized into three categories: power flow stability, DC voltage stability and dq-axis stability, and stability criteria are designed according to different stability. Based on the method of intersection of multiple stability regions and Z-plane projection, the SVSR is characterized. Finally, the influence of different parameter settings on the SVSR is analyzed, and the accuracy of the proposed method is verified by RT-Lab experimental platform.

WAMS Based Real-Time Voltage Stability Monitoring for Various Load Models in the Presence of a DFIG Integrated Wind Farm

With rising global energy demand, transmission lines are operated at their limits, causing electrical grids to operate under extreme voltage instability conditions. To meet the increased load-demand and the forced tendency across the globe of tilting towards even more renewable generation, solar and wind farms are integrated with increased size and capacity. These uncontrolled natural power injection again may affect the system’s voltage stability. To avoid blackouts and to achieve the maximum voltage stability of power systems, operators need to do effective real-time grid monitoring and control at load terminals. Load models are important in the analysis of voltage stability, and accurate load models are useful in analysing the voltage stability conditions. Phasor-measurement-unit (PMU) based wide-area monitoring and smart-automation is an innovative technology for measuring load voltage magnitude, phase angle, and frequency variations in a DFIG integrated large wind power system. This research paper focuses on estimating the real-time voltage stability through the use of linear, nonlinear, and dynamic load models in presence of a DFIG based wind-farm in WSCC three-machine nine-bus power network using PMU data. This study is carried out using MATLAB-Simulink software.

Intelligent based technique for under voltage load shedding in power transmission systems

<p>The increasing demand of electric power energy and the presence of disturbances can be identified as the factors of voltage instability condition in a power system. A secure and reliable power system should be considered to ensure smooth delivery of electricity to the consumers. A power system may experience undesired event such as voltage instability condition leading to voltage collapse or cascading collapse if the system experiences lack of reactive power support. Thus, to avoid blackout and cascaded tripping, load shedding is the last resort to prevent a total damage. Under Voltage Load Shedding (UVLS) scheme is one of the possible methods which can be conducted by thepower system operators to avoid the occurrence of voltage instability condition. This paper presents the intelligent based technique for under voltage load shedding in power transmission systems. In this study, a computational based technique is developed in solving problem related to UVLS. The integration between a known computational intelligence-based technique termed as Evolutionary Programming (EP) with the under-voltage load shedding algorithm has been able to maintain the system operated within the acceptable voltage limit. Loss and minimum voltage control as the objective function implemented on the IEEE 30-Bus Reliability Test System (RTS) managed to optimally identify the optimal location and sizing for the load shedding scheme. Results from the studies, clearly indicate the feasibility of EP for load shedding scheme in loss and minimum voltage control in power system.</p>

Development and Real-Time Implementation of an Under Voltage Load Shedding Scheme Using a Real-Time Digital Simulator

Generation, transmission, and distribution of electric power systems are extremely important to our modern society. It is critical to keep the power grid stable and reliable at all times. Individual power system reliability needs to be enforced to avoid a voltage drop due to contingencies such as a loss of generation or a sudden increase in a load demand. Voltage changes for a given increase in the load demand can lead to voltage instability conditions. The main factor causing instability is the inability of the power systems to meet the demand of the reactive power. This subject has been a concern over the last two decades and a lot of research work has been done in the area of voltage stability and control. Under-voltage load shedding schemes are commonly implemented as an emergency measure in cases where the voltage conditions are drastically dropping due to a sudden increase of the load demand in the system. This paper addresses the problem of designing and developing a robust and efficient Under-Voltage Load Shedding (UVLS) scheme for a real-time implementation in the power system networks. A new multi-stage adaptive UVLS scheme is developed in order to improve the operation and increase reliability and flexibility of the existing UVLS schemes. This scheme is implemented in real-time using RSCAD software environment of the Real-Time Digital Simulator (RTDS).

Probabilistic assessment of static voltage stability in distribution systems considering wind generation using catastrophe theory

With increasing penetration of distributed generations, the importance of the voltage stability assessment of distribution networks has been increased. Considering this situation, a probabilistic model is proposed to evaluate the voltage stability of distribution network integrating wind turbine (WT) units. With this intention, a probabilistic voltage stability index (PVSI) of a radial distribution system with wind power generation is presented. This index investigates the probabilistic risk of voltage collapse for all the buses of system considering uncertainty of WTs. Therefore, the most sensitive bus to the voltage collapse can be identified. The problem model is based on the catastrophe theory that can find the bifurcation point of system. Three-point estimation method is employed to calculate the statistical moments of voltage and PVSI of nodes. Moreover, to estimate the cumulative distribution function of output random variables, the Cornish−Fisher series are used. The performance of the probabilistic index is tested on the IEEE 69-bus radial distribution system where different load models are considered. The results demonstrate that the PVSI can accurately predict the voltage instability condition of the system.

Extended synchrophasor-based online voltage stability assessment using synchronous generator-derived indices

Summary This paper proposes and investigates the online application of generator-derived real-time voltage stability assessment indices in large interconnected power systems. The indices are based on synchrophasor measurements from synchronous generators and are used in the prediction of the system's margin to voltage collapse in real-time. Comparative analyses are carried out between the newly proposed indices, an existing effective generator reactive power reserve index, and two line-based indices. Results obtained from testing the proposed indices on the New England 39-bus test system show that the proposed indices are simple to implement, more responsive to system dynamics and provide a more accurate estimation of the system's margin to voltage collapse compared with the existing indices. Furthermore, the suitability of the proposed indices for small disturbance voltage instability and large disturbance voltage instability conditions were demonstrated. In addition, the proposed indices are subsequently deployed on a programmable logic controller for real-time closed-loop testing with the real-time digital simulator. Copyright © 2016 John Wiley & Sons, Ltd.

A STEADY-STATE APPROACH TO PREVENT VOLTAGE COLLAPSE IN POWER SYSTEM

This paper presents a steady state approach to prevent voltage collapse in a power system. The power systemoperation close to stability boundaries is an important factor which may lead to voltage instability conditions. Thereare different ways to prevent voltage collapse in the power system; one of this is the correct coordination of theprotection devices to avoid undesirable equipment disconnections.This paper proposes a new method to coordinatethe back-up zone in the distance protection scheme. The methodology uses both Optimal Power Flow (OPF) andContinuation Power Flow (CPF) solutions to determine the impedance seen by the relay. These impedances are latercompared to conclude which is the best option to set the parameter for the back-up zone in the relay. The methodologyalso considers the distance to Maximum Loading Point (MLP) and the corresponding Voltage Collapse Point(VCP). Therefore, undesirable disconnections can be avoided when the power system operates close to the stabilityboundaries. In order to demonstrate and validate the methodology, simulations are carried out on the IEEE 14-bus testsystem using MATLAB.

Stability Index Based Voltage Collapse Prediction and Contingency Analysis

Voltage instability is a phenomenon that could occur in power systems due to stressed conditions. The result would be an occurrence of voltage collapse leading to total blackout of the system. Therefore, voltage collapse prediction is an important part of power system planning and operation, and can help ensure that voltage collapse due to voltage instability is avoided. Line outages in power systems may also cause voltage collapse, thereby implying the contingency in the system. Contingency problems caused by line outages have been identified as one of the main causes of voltage instability in power systems. This paper presents a new technique for contingency ranking based on voltage stability conditions in power systems. A new line stability index was formulated and used to identify the critical line outages and sensitive lines in the system. Line outage contingency ranking was performed on several loading conditions in order to identify the effect of an increase in loading to critical line outages. Correlation studies on the results obtained from contingency ranking and voltage stability analysis were also conducted, and it was found that line outages in weak lines would cause voltage instability conditions in a system. Subsequently, using the results from the contingency ranking, weak areas in the system can be identified. The proposed contingency ranking technique was tested on the IEEE reliability test system.

Development of nonlinear predictor with a set of predicted points for continuation power flow

AbstractIn this paper, a new continuation power flow method is proposed to speed up computational time for drawing P– V curves in power systems. The continuation power flow calculation aims at successively evaluating power flow solutions in changing the nodal specified value of power flow calculation. The P– V curves are useful for static voltage instability. The conventional continuation power flow calculation methods are based on the predictor– corrector method. This paper proposes a new nonlinear predictor in the predictor– corrector method. The proposed method simultaneously evaluates a set of solution candidates through the nonlinear predictor. The effectiveness of the proposed method is demonstrated in sample systems. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(4): 30–41, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20297

可変ステップ可変次数予測子による連続型潮流計算

This paper proposes a new continuation power flow calculation method for drawing a P-V curve in power systems. The continuation power flow calculation successively evaluates power flow solutions through changing a specified value of the power flow calculation. In recent years, power system operators are quite concerned with voltage instability due to the appearance of deregulated and competitive power markets. The continuation power flow calculation plays an important role to understand the load characteristics in a sense of static voltage instability. In this paper, a new continuation power flow with a variable-step variable-order (VSVO) nonlinear predictor is proposed. The proposed method evaluates optimal predicted points confirming with the feature of P-V curves. The proposed method is successfully applied to IEEE 118-bus and IEEE 300-bus systems.

連続型潮流計算のための予測点集合を求める非線形予測子の開発

In this paper, a new continuation power flow method is proposed to speed up computational time for drawing P– V curves in power systems. The continuation power flow calculation aims at successively evaluating power flow solutions in changing the nodal specified value of power flow calculation. The P– V curves are useful for static voltage instability. The conventional continuation power flow calculation methods are based on the predictor– corrector method. This paper proposes a new nonlinear predictor in the predictor– corrector method. The proposed method simultaneously evaluates a set of solution candidates through the nonlinear predictor. The effectiveness of the proposed method is demonstrated in sample systems. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(4): 30–41, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20297

A neural network-based tool for preventive control of voltage stability in multi-area power systems

In this paper a neural network-based tool is proposed to provide on-line preventive control strategies capable to restore a multi-area power system to a secure operating point when a voltage instability condition is going to be reached. These strategies are, respectively, based on reactive power control actions, generating nodes voltage–magnitude control actions and load curtailment actions. After decomposing the power system into an appropriate number of areas, for each area a feed-forward neural network is trained to give as output to a defined set of inputs an area-based voltage-stability index. The voltage stability of the whole power system is characterised by the minimum value among the area indices. Thus, for a given operating condition, the most critical area is identified and remedial measures are considered only for a restricted region of the system. Since each net receives `internal' inputs and inputs from the remaining areas, it is shown that using the resulting neural network architecture appropriate algorithms can be developed to carry out on-line a preventive control strategy based on the above-mentioned types of control actions. The effectiveness of the proposed approach is tested on the IEEE 118-busbar, 19-machine power system.

Impact of secondary voltage control on voltage stability

In this paper, different operation modes of secondary voltage control in voltage instability conditions are investigated. The voltage instability considered here is caused by a critically high system load level. This level is determined and studied in the presence of the primary voltage control and in the presence of both the primary and the secondary voltage controls. The system behavior is analyzed next, using the method of dynamic bifurcation. Finally, an emergency assist mode of secondary voltage control in voltage instability conditions is proposed and examined.

SYSTEM L0ADAB1LITY VERSUS BUS LOADABILITY FOR VOLTAGE INSTABILITY

ABSTRACT The techniques used to evaluate the limiting point and hence the security margin between the operating point and the voltage collapse point are considered the most accurate method in static voltage instability studies. Two such approaches are compared: the system loadability ( and its associated sensitivity parameters ) versus the bus loadability at a predetermined set of buses. The mathematical models for the two approaches are unified and the same nonlinear optimization technique (Augmented Lagrangian Multipliers ) is used to solve the two problems in order to obtain comparable results. Three different systems are used in the comparison: a 20-bus, a 30-bus and a 57-bus systems.