Renuga Verayiah

A Study on static voltage collapse proximity indicators

In the time of rapid growth, there is an increase of demand for a reliable and stable power supply. Due to this, utility companies are forced to operate their power system nearer to its maximum capabilities since system expansion may be a costly option. As a result, the power system will be at risk to voltage collapse. Voltage collapse phenomenon is known to be complex and localised in nature but with a widespread effect. The ultimate effect of voltage collapse would be total system collapse which would incur high losses to utility companies. Thus, on- line monitoring of power system stability has become a vital factor for electric utility companies. This paper looks into combining a power flow program in MATLAB environment with two line stability indices, which are fast voltage stability index (FVSI) and line stability index, LQP for automatic contingency ranking. The IEEE 14 Bus Test System is used as a standard test system. This approach investigates each line of the system through calculating an indicator that varies from zero (no load condition) to unity (maximum permissible loading condition). The basic concept of maximum power transfer through a line is utilized. Correlation study on the results obtained from contingency ranking and voltage stability analysis were conducted and it is found that line outages at the weak lines would cause voltage instability condition to a system. Subsequently, using the result from the contingency ranking, weak areas in the system can be identified. Verification of this technique with other existing technique shows a strong agreement between them.

A study on FVSI index as an indicator for under voltage load shedding (UVLS)

In the time of rapid growth, there is an increase of demand for a reliable and stable power supply. Power utilities are pressured to cater the rising demand with the existing system. Thus, monitoring the voltage stability of the system has become crucial. Under Voltage Load Shedding (UVLS) is one of the many methods that are used to sustain voltage stability. On the other hand, Fast Voltage Stability Index (FVSI) index is proven to be a good indicator for voltage stability in a system. This paper will study on the correlation between FVSI index and UVLS scheme. From the simulation, the results clearly indicate that FVSI index can be used to indentify location to be load shed.

Modified Novel Line Stability Factor Index with Reactive Power Tracing for Identification of Vulnerable Buses in Power System

Many power tracing techniques have been developed but are limited to the application of transmission service pricing in a deregulated environment. To expand the knowledge of power tracing theory and its application, this paper adopts the power tracing theory into voltage stability improvement. This paper proposes a modified novel line stability factor index with load tracing capability known as LQP_LT for the purpose of finding the appropriate locations in a power system network for any preventive and corrective actions. Unlike the commonly applied real power tracing, this method presents the reactive power tracing utilizing the proportional sharing method (PSM) with all the line reactive losses being taken into consideration in the network study with the system size remain the same. IEEE 5 bus system is used to demonstrate the LQP_LT concept and all the results obtained are compared with modified Fast Voltage Stability Index with load tracing ability (FVSI_LT). The results obtained found to be efficient in determining the reactive power contributed by a certain load bus in a transmission line which ultimately responsible to cause a stressed line and overall voltage instability in a system.

Under Voltage Load Shedding (UVLS) study for 746 test bus system

Voltage collapse phenomenon is known to be complex and localized in nature but with a widespread effect. The ultimate effect of voltage collapse would be total system collapse which would incur high losses to utility companies. Thus, on- line monitoring of power system stability has become a vital factor for electric utility companies. One of the methods to avoid voltage collapse is to perform Under Voltage Load Shedding (UVLS). Fast Voltage Stability Index (FVSI) index is proven to be a good indicator for voltage stability in a system. This paper analyzes the correlation between FVSI and the placement of UVLS relays for a 746 test bus system. It is found from the simulations results that FVSI index can be used as an indicator for the placement of UVLS relays in a power system network.

Study on P-V Curve and V-Q Curve of an Unbalanced Three- Phase System with Different Static Loads

P-V curve and V-Q curve (often term as Q-V curve) are widely used for planning and operation studies. The P-V curve and V-Q curve of an unbalanced three-phase system, unlike the balanced three-phase system, may not have similar loading margin (LM) and reactive power margin (RPM) on each phase. Therefore, DIgSILENT Programming Language (DPL) has been used to study the maximum loading point (MLP), critical point (CP), and also minimum reactive power point (MRPP) on each phase of an unbalanced three-phase system with different static loads. The tracing direction of P-V curve of each phase and the LM and RPM of each phase obtained from the P-V curve and V-Q curve for different static loads are also discussed. On top of that, continuation power flow (CPF) has become a common method to study the MLP. Hence, a simple 2-bus balanced three-phase system is used to validate the result obtained from the DIgSILENT with CPF method. Streszczenie. Krzywe P-V I V-Q w systemie trojfazowym niezrownowazonym mogą nie miec tego samego marginesu obciązenia LM i marginesu mocy biernej RPM w kazdej z faz. Zastosowano jezyk programowania DIgSILENT do określenia maksymalnego punktu obciązenia MLP, punktu krytycznego CP i punktu minimalnej mocy biernej MRPP. Analiza krzywych P-W i V-Q w niezrownowazonym ukladzie trojfazowym o roznych obciązeniach statycznych

Multi- level optimization strategy for load shedding with tracing capability index

Numerous stability indices have been developed to assess the voltage stability of power networks, since it is a powerful tool to identify the weakest bus and critical lines. To expand the knowledge of power tracing theory and its application into voltage stability assessment, this paper adopts the power tracing capable index into load shedding scheme. A modified novel line stability factor index with load tracing capability known as LQP_LT is used to classify the weak buses according to its priority rank for load shedding bus selection. IEEE 5 bus system is used to demonstrate the LQP_LT principles and concepts. The results obtained from the weak bus identifications is analyzed for load shedding optimization execution. Particle Swarm Optimization (PSO) is used for the optimization analysis in a multi- level approach and objective settings. The results obtained post- load shedding with the proposed method is found to be efficient for the implementation and execution of optimized amount and location selection for under voltage load shedding scheme.

Performance Comparison of Voltage Stability Indices for Weak Bus Identification in Power Systems

Voltage collapse event is identified as complex and localized in nature but its effect is extensive once occurred. The vital effect of voltage collapse would be the total system collapse or blackouts which would cost a large loss to utility companies. Eventually, on- line monitoring of power system stability has become an important factor for electric power utilities. The last utmost option to avert voltage collapse incident from occurring is by the implementation of under voltage load shedding scheme. The identification of location for load shedding is the main motivation of the study. The weakest bus in a power system is identified as the location for load shedding. This location is obtained using voltage stability index Ld. The performance and effectiveness of Ld index is compared with Fast Voltage Stability Index (FVSI) and Le Index. The results obtained indicate that Ld Index can be used to identify the weak bus in a power system and consequently for the placement of UVLS relays in a power system network.

Impact of static load on voltage stability of an unbalanced distribution system

Static load which is known for three different characteristics i.e. constant power, constant current and constant impedance shows a different voltage profile because both of their real power and reactive power vary differently as the voltage varies except for constant power. This paper will analyze the impact of each load characteristic individually and also as combination on voltage stability of an IEEE 34 Bus Distribution System by increasing the load demand, and also transient analysis i.e. creating a single phase-to-ground fault i.e. on phase a and balanced three phase fault. The most suitable load to study the voltage stability is also proposed. It was found that, with constant power loads, the reactive power demand increases significantly when load real power and reactive power increases by 25%. Constant current loads and combination loads, on the other hand, the reactive power demand increases but only slightly and the demand is even lesser when with constant impedance loads. However, as the load real power and reactive power increases by 50%, constant power loads causes voltage collapse whilst constant current loads and combination loads turn out to be the next in the order followed by constant impedance loads. In transient analysis, during the single phase fault, with combination loads, phase b voltage increases drastically but only small increment observed in phase c voltage. During the three phase fault, phase b voltage is slightly higher than phase c voltage followed by phase a voltage. As comparison to combination loads, constant power loads causes lesser three phase voltages. After the fault was cleared, a smooth voltage waveform obtained in the period of retaining back to the same pre-fault voltage, however, distortions in the voltage recovering waveform seen when dynamic load included in the system. Constant power load is found to be the suitable load to study the voltage stability.

Development of multi-objective load shedding optimization via back tracking search algorithm with novel reactive power tracing index

This paper demonstrates on the development of weak bus identification method using novel reactive power tracing index for determination and selection on appropriate buses for load shedding purpose. Power tracing principles using downstream looking algorithm is utilized for the development of a novel reactive power tracing index known as LQP_LT. The results obtained from the weak bus identification from various power system contingencies are analyzed for determination of the load shed amount. Optimization on the total amount of load shed is customized based on multi-objective functions via backtracking search algorithm. The objective functions are set to minimize the amount of load shedding and to minimize the total LQP_LT indices for all buses. A standard IEEE 57 test bus system is used as a data platform for the power flow simulations carried out in MATLAB environment. The results obtained post-load shedding for the proposed method is found to be robust, efficient and reliable for the implementation and execution of optimized amount and location selection for Under Voltage Load Shedding scheme in large network.