Voltage Collapse Risk Associated to Under-Voltage Capacitive Compensation in Electric Power System Operation

Abstract

<b>Problem statement: </b>In the operation of an Electric Power System (EPS), it has been usual to provide reactive power injection to avoid an under-voltage bus condition. In some situations an adequate voltage profile will not be a guarantee against Voltage Collapses (VCs) that may cause blackouts as seen in many occurrences around the world. The repeatedly injection of reactive power can turn a bus into a characteristic too much capacitive. Under this condition and in the presence of a considerable percentage of the constant power load type, there will be a high risk of a VC. Any of the indices proposed in the literature as VC Proximity Indicators (VCPIs) may alert the operator about the risk.<b> Approach: </b>In order to elucidate the problem stated, simulations were performed using MatLab/SimPowerSystems. It was used a basic example system composed by an infinite-bus feeding, through a large impedance line, a bus load whose power could be increased in ramp manner. It is also included a shunt capacitive compensation at the load bus every time the voltage value reaches 0.9 pu. Therefore, the VC risk increase could be shown by means of graphic results and the indications of some VCPIs sensitivity indices (including the new proposed index). <b>Results:</b> The graphics obtained in this study is a contribution to illustrate the voltage collapse risk problem when dealing with adjustments of voltage profile to meet the system requirements. Also, a VCPI sensitivity indicator using apparent load power was tested. The results have shown that all VCPI responses are very similar for a given case and electric system. <b>Conclusion/Recommendations:</b> Any VCPI information can help in the decision stage between either more reactive power injection or load shedding. A routine can also be developed for a supervisory program in order to alert the operator about VC risks

Electric Power System Under-Voltage Load Shedding Protection Can Become a Trap

“…This phenomenon could be a trap to the operator if he was trusting in UVLS protection, because a too capacitive bus situation can turn it ineffective. The undesirable aspect of a very capacitive load bus was explained in the last study of the same researchers published in this journal [1] . The UVLS scheme is based on the supposition that the VC could happen after the protected load bus voltage remained below a limit (0.92 pu for instance) for several seconds.…”

Optimal Control Design of Static Var Compensator for Damping Power System Oscillation

“…Flexible AC Transmission System (FACTS) controllers, based on the rapid development of power electronics technology, have been proposed for power flow control in steady state and dynamic state. (Barbuy et al, 2009;Kumkratug, 2011;Rudez and Mihalic, 2009).…”

Application Lyapunov Theory to Determine Control Strategy of Static Var Compensator for Damping Power System Oscillation

“…A number of Flexible AC Transmission System (FACTS) controllers, based on the rapid development of power electronics technology, have been proposed for power flow control in steady state and dynamic state. (Barbuy et al, 2009;Kumkratug, 2010).…”