Voltage stability assessment of the national grid system. Ac contingency analysis is based on an ac load flow model, referred to. Pv curve or nose curve for wind farm1 with statcom 73. Nov 10, 2010 lec35 voltage stability part1 nptelhrd. Scope and objective in this thesis, a viable alternative to the newtonraphson power flow is presented and applied to the investigation of steady state voltage stability. The p v and v q analyses are carried out for bus 4 in the test system. For this analysis, power of the load at a particular bus is increased in steps and voltage. Bonneville power administration uses the conven tional p v and q v curves as a tool for assessing the voltage stability of the system. The v q curve power flow method is widely used by western systems coordinating council. V q curve is a characteristic of both the network and the load q1 and q2 are reactive power margins with respect to the loss of operating point. Pdf determination of steadystate voltage stability limit. Pv curve or nose curve for wind farm1 without facts 72 figure 4. Keywords statcom, voltage stability, generator sensitivity based method, v q curve analysis, coherent bus groups, rrb, anderson and fouad 9 test bus.
Power system voltage stability old version duration. Power quality and voltage stability of power systems with. Explanatory materials for technical assistance on system. Power system voltage stability analysis raiith iit hyderabad.
P v and q v curves are commonly used to determine the steady state voltage stability limit of a power system. Curve under fault conditions pq v characteristics and voltage stability voltage instability phenomena supplement 1. The reactive power margin is the mvar distance between the operating point and the nose point of the v q curve. Voltage stability or voltage collapse deals with the ability of a power system to maintain acceptable voltage levels at all buses in the system in any condition whether it is normal or during disturbance. Voltage stability analysis comparing generator sensitivity. The curve is plotted on the splane, where p is the vertical axis and q is the horizontal axis. A system is in a stable mode with respect to voltage if v q sensitivity. Voltage stability depends on how the variations in q and p affect the voltages at the load buses. The point where dqdv is zero is the point of voltage stability limit 1. The conventional methods can be broadly classified into the following types. Evaluation of voltage stability by p v curve image of p v curve or nose curve operating voltage pmargin. Voltage stability software voltage stability analysis.
The point where dqdv is zero is the point of voltage instability. The q v curve can be used as an index for voltage instability. The reactive load at bus 4 when the p v analysis is carried out and the active load at bus 4. Notes on power system voltage stability iit kanpur. Pv, qv curve a novel approach for voltage stability.
Capability curve of a synchronous generator circuit globe. Jun 30, 2018 voltage stability analysis using q v curves. Analysis of steady state voltage stability in large scale. Countermeasure against voltage stability shunt caps. This paper presents the analysis of voltage instability of electric power system by using powervoltage pv curve and reactive powervoltage qv. A visualization framework for assessing voltage stability margins is. Voltage stability analysis using qv curves in power world. The projections of voltage stability region and pq v curve on pq plane are shown in fig. A pq v curve shows the boundary of the maximum realreactive power and the minimum voltage magnitude in a threedimensional diagram. The more prominently applied methods in voltage stability analysis are those that try to define an index using the system load margin. Qv relationship shows the sensitivity and variation of bus voltages with respect to reactive power injections or absorptions. V q curve is a characteristic of both the network and the load q1 and q2 are reactive power margins with respect to.
Pdf determination of steadystate voltage stability. Test results and discussion the voltage stability analysis is performed on ieee 30 bus system. The p v and q v curves are nonlinear at the maximum permissible power point. Voltage stability dynamics voltage stability involves large disturbance, nonlinear, discontinuous dynamics load restoration concepts understood from firstorder differential equations highly oversimplified stabilizing actions must be timely to ensure region of attraction to postdisturbance operating point equilibrium point. Capability curvebased generator protection minimizes. An approaches, model analysis of the modified load flow jacobian matrix, has been used as static voltage stability index to determine vulnerable buss voltage stability problem 7. Voltage stability modelling and system protection scheme. Voltage stability is a local phenomenon, but its cost may have a extensive impact. V q 17 from the power angle curve shown in figure 1. Austria is with power technologies pti, schenectady, ny 12305. Pv and qv curve analysis of ieee 9 bus system ijera.
Voltage instability on the other hand is the opposite of voltage stability. Voltage stability studies the effect of variation in reactive power on the voltage of the system. Inorder to determine the maximum permissible load static voltage stability limit of a power system p v and q v curves are used. Transient stability and dynamic stability case study four. P v or q v curves are generated for comparison in this step. Several analysis methods are available for longterm voltage stability. Open circuit voltage buildup overheads pdf stator transform sb. Sep 28, 2015 v q curve method and reactive power reserve. V v v upper 26 especially the lower value is the critical value cr v from the point of view of avoiding voltage. Voltage stability assessment using pq region incorporating. One problem with q v curve method is that by focusing on a small number buses, the systemwide voltage stability problem will not be readily unveiled. One approach to investigate static voltage stability is to. For normal operation of oltc of transformer with turn ration 1.
Generator capability curve the gcc defines the generator operating limits in the p q plane, as shown in fig. Voltage stability assessment using pq region incorporating wind power by you wang the university of wisconsinmilwaukee, 20 under the supervision of professor david c. Voltage instability analysis using pv or qv analysis by. The voltage support function of the midpoint compensation can easily be extended to the. Pv, qv curve a novel approach for voltage stability analysis. Pdf voltage instability analysis on pv and qv curves for radial. For this analysis, power of the load at a particular bus is increased in steps and voltage is observed. P v curve and knee point the receiving end voltage is plotted in fig. Literature survey shows that a lot of work has been done on the voltage stability analysis of transmission systems 4 but very little work has been reported on the voltage stability analysis of radial distribution systems. Forward current versus voltage the standard equation for current through a diode is. Voltage stability assessment using p q region incorporating wind power by you wang the university of wisconsinmilwaukee, 20 under the supervision of professor david c. Keywords statcom, voltage stability, generator sensitivity based method, v q curve analysis, coherent bus groups, rrb, anderson and fouad 9. Voltage instability occurs due to the failure of the power system to supply ample power to cover the increased demand of. The constant excitation locus is a circle with center o and radius ob.
Voltage stability region projected on pq plane and pq boundary. Yu voltage stability assessment vsa is a significant part in planning and operating of the power system. Tools for voltage stability analysis different methods exist in the literature for carrying out a steady state voltage stability analysis. For constant power ia and voltamperes s va, the locus is a circle with center at o and radius ob 3 v p i a.
This method, called the continuation power flow is more numerically robust than existing methods. The phenomenon of voltage stability is very often illustrated by the so called nosecurve. Voltage stability analysis has become more important as a. Increasing the load beyond this point results in voltage collapse where the reactive power demand is larger than the supply. Pdf pv and qv curves approach for voltage instability analysis. For critical buses, qv curves are generated and their reactive power margins are calculated to crosscheck the modal analysis result. This paper presents study of different methods and techniques used to improve the voltage stability of electrical power systems. Voltage stability analysis of radial distribution networks. Voltage stability has become a very important issue of power systems analysis. Power system voltage stability linkedin slideshare.
V curve, the voltage drops rapidly with the increase in loads. With this perspective, a new approach to the assessment of voltage stability margins based on the pq v curve technique is proposed. Some of the conventional methods widely used are classified into the following types. Generator capability curve the gcc defines the generator operating limits in the pq plane, as shown in fig. P v curve analysis is used to determine voltage stability of a network. In this letter, a new method of determining the voltage stability limit using the pq. Conducting an effective voltage stability analysis is essential for system planning and longterm interoperability. Vijay vittal, cochair daniel tylavsky, cochair jiangchao qin arizona state university may 2017. Produce the new solutions for the selected onlooker bee, depending on the value, using eqs. A thesis presented in partial fulfillment of the requirements for the degree. Q sensitivities can also be used as indicators of voltage stability voltage stability studies.
P v curves are useful for conceptual analysis of voltage stability especially for radial systems. Explanatory materials for technical assistance on system planning voltage stability 1. Voltage collapse index based on pv curves, qv curves. Jasmon and lee 5 and guleina and strmchnic 6 have studied the voltage stability analysis of radial distribution systems. This brings the stable equilibrium point s closer to the critical point u. Lindex sensitivity based voltage stability enhancement.
The point where dqdv is zero is the point of voltage stability limit 3. The phenomenon of voltage stability is very often illustrated by the so called nose curve, see figure 1, where the receiving end voltage in a transmission system is plotted against the receiving end real power the power factor or the reactive power is often used as a parameter. Unlike the p v curve method, it doesnt require the system to be represented as twobus equivalent. Presentation pss stability theory electric power system. Analysis of voltage stability using lindex method i. Pdf voltage instability analysis on pv and qv curves for. Effect of generator q limit violation of generator q limit will further shrinks the p v curve as shown, it again worsen the voltage stability. Voltage stability indices indicators v q sensitivities. Network configurations and load distributions can also reflect using pv curve.
For examining the steady state voltage stability, we can make use of the p v curves and v q curves as defined in the following section. Voltage stability analysis provides assessment of weak, unstable or uncontrollable areas of the electrical network that may jeopardize future load growth due to unexpected voltage collapse. The final step is to verify the dynamic voltage stability response to the contingencies via timedomain simulation, including the impact of different load models. Transientdynamic stability, pqv characteristics and. Voltage instability analysis using p v or q v analysis by weili yi a thesis presented in partial fulfillment of the requirements for the degree master of science approved april 2017 by the graduate supervisory committee. The curve shows the distance between current operating point and collapse point. The prominent methods in voltage stability analysis are those that find system load margin, especially when system contingency is considered p v curve and q v curve are most considerable method to find active power margin and reactive power margin. Q3 provides a measure of the mvar distance to system operability. Pdf pv curve approach for voltage stability analysis. Voltage security of a bus is closely related to the available reactive power reserve, which can be easily found from the v q curve of the bus under consideration. The investigations for v q curve and the novel generator sensitivity method are carried out and compared on anderson and fouad 9 bus test system.
A new approach to the assessment of steadystate voltage. Generalized voltage collapse q v curves overheads pdf reclosure time pdf reclosure time mcd phasor diagrams pdf phasor diagrams mcd q v curves pdf q v curves mcd no assignment that will be collected. Thevenins equivalent based pqv voltage stability region. Various techniques exist in the literature for implementation of voltage stability analysis. Power system stability analyses of the pv and vq curves for. A loss of synchronism can cause large pulsations in voltage and current can further jeopardize the power system and that negatively impact stability. V c is the voltage at the bottom of q v curve, which is the minimum voltage. P v, q v curve a novel approach for voltage stability analysis operators need to know not only the severity of their system, but also the mechanisms that cause voltage instability. The qv curve can be used as an index for voltage instability. I is the current through the diode i s is the reverse saturation current v is the voltage across the diode can be positive or negative n is a junction constant typically around 2 for diodes, 1 for transistors. Determine the abandoned solution for the scout bees, if it exists, and replace it with a. Good surveys of the voltage stability discipline can be found in references 1,4,11, where theory as well as analytical tools and industrial experience are presented. Constant p operation lies on a line parallel to q axis.
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