Weak Buses Research Articles

Enhancement of Transmission Efficiency and Voltage Profile in the Bauchi Axis of Nigerian Power Grid Using a VSC-HVDC System

Increasing electricity demand occasioned by increased population and advancement in economic activities makes it mandatory to upgrade the Nigerian power grid. The ongoing construction of a new hydropower plant at Mambila Plateau in Taraba State of Nigerian is a response to this call. Performance evaluation of the Nigerian power grid expanded to include the new power plant has revealed the occurrence of poor voltage profile accompanied by colossal power losses mostly in the Bauchi region. This paper explores the techniques for addressing this challenge by the integration of voltage source controlled high voltage direct current (VSC-HVDC) transmission system into the expanded Nigerian 41- bus 330kV transmission grid network at the weakest areas. The HVDC converter is introduced into the power grid as an extra bus, and all impedance elements in the HVDC system transformed to the grid side. This action merges the two converter stations into a single bus to produce an entirely high voltage alternating current (HVAC) system, thereby making it possible to apply conventional power flow techniques. This model was verified by the simulation of the modified network in Matlab Simulink environment. Performance evaluation of the expanded network prior to the connection of HVDC system identified the transmission line between the Jalingo bus and the Mambila power plant as the weakest area, which was consequently selected as the optimal location for the proposed VSC-HVDC system. Power flow analysis of the modified network with the inclusion of HVDC system revealed a remarkable improvement in voltage magnitude at the weak buses, and minimized power losses in the system. This implies that such a project is worth undertaking. Therefore, the enhancement of voltage profile using the VSC-HVDC transmission system is a panacea for curbing the expected line losses that may arise while evacuating power from the proposed Mambila plant.

A power flow adjustment strategy based on weak bus identification and new bus type conversion

The power flow solvability is greatly challenged by the growing pressure on power grid induced by the rapid development of economy. The approaches of restoring power flow solvability should be profoundly studied. Most of adopted power flow adjustment methods are based on manual interference which require extensive human resources with inefficiency. Thus, a power flow adjustment strategy based on a weak bus identification and a new bus type conversion is proposed. A weak bus identification index is defined and expressed when power flow has no solution. We propose a novel bus type and a concept of the power shortage to restore power flow solvability. The generator action set is determined by calculating the left eigenvector of the Jacobian matrix. At last, we establish a linear programming model to determine the generator output adjustment. Numerical results are obtained in 3 test systems and an actual system in China. Compared with other methods, the proposed method is verified to have a higher success rate of restoring power flow solvability and has robustness in various scenarios.

Online Monitoring of Voltage Stability Margin in Kosovo Power System Using Local Measurements

This paper presents an analysis of the voltage stability of the Kosovo power system. The first part of the study has included a detailed analysis of the Kosovo power system by using the continuous power flow method, with an emphasis on the determination of the P–V curve of voltage stability. Thus, it has identified the weak and critical points of the power system in terms of voltage stability and has defined the margin of instability. In order to achieve online monitoring of voltage stability in the power system, it is proposed to place phasor measurement units in the weakest critical buses. Furthermore, the Thevenin equivalent method has been applied to evaluate voltage stability in the critical buses. The maximum transmissible real power to the weak buses in the system can be achieved when load impedance is equal to the Thevenin impedance. The load and Thevenin impedance values have been obtained from the relevant PMU data. Following online monitoring of voltage stability in the power system, the developed voltage stability load bus index can be used as useful information by system operators in order to undertake appropriate countermeasures to prevent voltage collapse.

Voltage Stability Index Using New Single-Port Equivalent Based on Component Peculiarity and Sensitivity Persistence

A voltage stability index is proposed using a new single-port equivalent depending on component peculiarity representation and sensitivity persistence to locate and determine long-term voltage instability in transmission and distribution power networks. The suggested single-port equivalent effectively represents the equivalence of various component types and assures the consistency of sensitivity information before and after the equivalence which is compulsory for the equivalent accuracy in estimating the voltage stability analysis. The stability index is derived from the new single-port equivalent to determine the system voltage instability. The proposed stability index is compared with indices based on virtual impedance and Thevenin impedance models. This new stability index shows more accuracy and effectiveness as compared to the indices based on virtual and Thevenin equivalent models. The index also determines the weak buses, where an improvement or functional measure can be used to reduce the system voltage instability. The validity of the proposed equivalent approach and stability index is presented by utilizing two radial systems, four IEEE systems and an actual system having bus size from five to 1010 buses.

Under voltage load shedding using hybrid ABC-PSO algorithm for voltage stability enhancement

Voltage collapse tends to occur due to the voltage instability created during large faults. As a last resort, under-voltage load shedding (UVLS) is performed after all the available power operation and control mechanisms have been exhausted. Load shedding techniques have advanced from the conventional and adaptive methods that are less optimal compared to computational intelligence-based techniques. Recent works have identified hybrid algorithms to give more optimal solutions for UVLS problems with multi-objective functions. In this paper, a novel hybrid ABC-PSO algorithm, adapted from a software estimation project, is used to perform UVLS on a modified IEEE 14-bus system. Eight overload conditions are imposed on the system ranging from 105% to 140% loading, where FVSI ranking is used in identifying weak buses. The load shedding is then performed following decentralized relay settings of 3.5 seconds, 5 seconds and 8 seconds, which gives an overall 99.32% recovery of voltage profiles. The proposed hybrid ABC-PSO algorithm is able to shed optimal amounts of load, giving an 89.56% post-contingency load, compared to GA's 77.04%, ABC-ANN at 84.03% and PSO-ANN at 80.96%. This study has been simulated on MATLAB software, using the Power System Analysis Toolbox (PSAT) graphical user and command-line interfaces.

재생에너지 시나리오 모델링 기반 확률론적 정태 안정도 해석

As the proportion of large-scale variable power generation increases, it is necessary to secure the grid reliability and flexibility of the power system. In addition, it is necessary to analyze the probabilistic security analysis considering the output variability of renewable energy. In this paper, scenarios reflecting the characteristics of renewable energy were created through the renewable energy output scenario modeling based on Monte Carlo Simulation. The scenario is used as input data for calculation of steady state and AC contingency solution assumed power flow, and probabilistic security analysis of branch flow and bus voltage was performed on the practical power system. The proposed algorithm can be used for decision making to establish a stable power system operation and plan according to the large-scale variability power system connection by analyzing the weak branches and buses according to the fluctuations in the output of renewable energy.

Assessment of voltage stability based on power transfer stability index using computational intelligence models

<span>In this paper, the importance of voltage stability is explained, which is a great problem in the EPS. The estimation of VS is made a priority so as to make the power system stable and prevent it from reaching voltage collapse. The power transfer stability index (PTSI) is used as a predictor utilized in a PSN to detect the instability of voltages on weakened buses. A PSI is used to obtain a voltage assessment of the PSNs. Two hybrid algorithms are developed. The (CA-NN) and the (PSO-NN). After developing algorithms, they are compared with the actual values of PTSI NR method. The algorithms installed on the 24 bus Iraqi PS. The actual values of PTSI are the targets needed. They are obtained from the NR algorithm when the input data is V<sub>i</sub>, δ<sub>i</sub>, P<sub>d</sub>, Q<sub>d</sub> for the algorithm. The results indicate that a weak bus that approaches voltage collapse and all results were approximately the same. There is a slight difference with the actual results and demonstrated classical methods are slower and less accurate than the hybrid algorithms. It also demonstrates the validation and effectiveness of algorithms (CA-NN, and PSO-NN) for assessing voltage-prioritizing </span><span>algorithms</span><span> (CA-NN). The MATLAB utilized to obtain most of the results.</span>

Statistical method for identification of weak nodes in power system based on voltage magnitude deviation

Identification of weak buses in an electric power system is important for operational and planning purposes. In this paper, a framework that uses the variance of the magnitude of voltage at load buses when reactive power of all loads are varied concurrently is used to identify a set of weak buses. In the framework, reactive power for all load buses are generated concurrently and independently based on the probability distribution function of load demands at each node. Three IEEE test systems are used to test the framework in Pypower in conjunction with Python programming language. The result shows that weak buses can be identified with the framework. It was observed that the first three set of most critical nodes in a network can be identified within a variation of 1% of reactive power at load nodes in case of ordinary power flow (pf), while the same set of nodes can be identified with at least 5% of variation of reactive power at nodes based on optimal power flow (opf). One area of application of this work could be in the use of the variance of voltage magnitude measurements to quickly identify a subset of weak nodes in a network.

A Voltage Stability-Based Approach to Determining the Maximum Size of Wind Farms in Power Systems

Current methods to determine the wind farms maximum size do not consider the effect of new wind generation on the Voltage Stability Margins (VSMs). Installing wind power in one area may affect VSMs in other areas of the power system. Buses with high VSMs before wind power injection may be converted into weak buses after wind power injections in other parts of power systems, which may lead to limited future wind farms expansion in other areas. In this paper, two methods are proposed to determine two new wind farms maximum size in order to maximize wind power penetration level. In both methods, the size of any new wind farm is determined using an iterative process which is increased by a constant value. Proposed methods were used in the IEEE 14-bus power system. The results of applying these new methods indicate that the second method results in higher maximum sizes than the first method.

A Comparison of Generalized Unified Power Flow Controller and Load Tap Changing Transformer for Voltage Stability Enhancement in a Power System

The continuous increase in power demand and huge power losses in modern power systems have been a growing concern to power utilities. Such phenomenon often results in epileptic power supply, power system instability, supply fluctuations and security problems in many parts of the globe. Identification of suitable places for the installation of reactive power compensators to minimize voltage drop and system power losses in a power system becomes imperative. In this paper, the Newton-Raphson iterative method was used for the power flow solution of the 28 bus Nigerian 330KV grid system. The Generalized Unified Power flow Controller (GUPFC) is installed at identified weak load buses of the Nigerian 28-bus power system to reduce the losses and voltage drop of the system. A comparative analysis of the GUPFC with Load Tap Changing Transformers (LTCT) is also performed. Result obtained shows that the GUPFC can largely (effectively) improve the system power stability and selectively balance the power flow of multi-lines power flows when placed at identified weak buses compared with LTCT. Thus, GUPFC can be used to reduce overall power losses along transmission lines as well as improve stability overall reliability of the power grid system.

Load Flow Analysis in Hybrid AC-DC Transmission Network

Power-flow studies are of great significance in planning and designing the future expansion of power systems as well as in determining the best operation of existing systems. Technologies such as renewables and power electronics are aiding in power conversion and control, thus making the power system massive, complex, and dynamic. HVDC is being preferred due to limitations in HVAC such as reactive power loss, stability, current carrying capacity, operation and control. The HVDC system is being used for bulk power transmission over long distances with minimum losses using overhead transmission lines or submarine cable crossings. Recent years have witnessed an unprecedented growth in the number of the HVDC projects. Due to the vast size and inaccessibility of transmission systems, real time testing can prove to be difficult. Thus analyzing power system stability through computer modeling and simulation proves to be a viable solution in this case. The motivation of this project is to construct and analyze the load flow and short circuit behavior in an IEEE 14 bus power system with DC link using MATLAB software. This involves determining the parameters for converter transformer, rectifier, inverter and DC cable for modelling the DC link. The line chosen for incorporation of DC link is a weak bus. This project gives the results of load flow and along with comparison of reactive power flow, system losses, voltage in an AC and an AC-DC system.

Voltage Profile and Sensitivity Analysis for a Grid Connected Solar, Wind and Small Hydro Hybrid System

Due to increase in integration of renewable energy into the grid and power quality issues arising from it, there is need for analysis and power improvement of such networks. This paper presents voltage profile, Q-V sensitivity analysis and Q-V curves analysis for a grid that is highly penetrated by renewable energy sources; solar PV, wind power and small hydro systems. Analysis is done on IEEE 39 bus test system with Wind power injection alone, PV power injection alone, with PV and wind power injection and with PV, wind and micro hydro power injection to the grid. The analysis is used to determine the buses where voltage stability improvement is needed. From the results, it was concluded that injection of the modeled wind power alone helped in stabilizing the voltage levels as determined from voltage profiles and reactive power margins. Replacing some of the conventional sources with PV power led to reduction of voltages for weak buses below the required standards. Injection of power from more than one renewable energy source helped in slightly improving the voltage levels. Distribution Static compensators (D-STATCOMs) were used to improve the voltage levels of the buses that were below the required standards.

A modal analysis based on reactive power compensation on 6-bus Oman electrical grid

This paper covers the modal analysis application (MATLAB 2019a) for improving the voltage profiles by optimum positioning of the capacitor banks for 6-bus Oman Electrical System because the Oman electricity TransmissionCompany (OETC) is suffering of drop voltage in these 6 buses especially during summer season as a peak period. The Newton-Raphson (N-R) method will help to determine the required reactive power for each load bus and as well the ideal position or point of capacitors. The process aims to maintain the Q-V relations of the electrical grid by correlating the lowest Eigen-values to related Eigen-vectors in obtained Jacobian matrix. It depends on the Eigen-values, if they are positive then the system’s voltage is stable otherwise it is not stable. In a stable system, the potential voltage collapse could be anticipated by checking the participation factors for a group of minimal positive Eigen-values. In general, the critical weak bus is associated with lowerEigen-values. Electrical system collapse is attributable to the weakest bus in the network and it could be avoided by determining the weak buses and providing capacitor banks at suitable locations which will lead to improve the voltage stability margin.

Improvement the voltage stability margin of Iraqi power system using the optimal values of FACTS devices

The detection of potential voltage collapse in power systems is essential to maintain the voltage stability in heavy load demand. This paper proposes a method to detect weak buses in power systems using two stability indices: the voltage stability margin factor (dS/dY) and the voltage collapse prediction index (VCPI). Hence, the paper aims to improve the voltage stability of Iraqi transmission grid by allocating FACTS devices in the optimal locations and optimal sizes. Two types of FACTS are used in this paper which are Thyristor controlled series compensator (TCSC) and static var compensator (SVC). The objective function of the problem is fitted using particle swarm optimization (PSO). The proposed method is verified using simulation test on Diyala-132 kV network which is a part of the Iraqi power system. The results observed that improvement the voltage stability margin, the voltage profile of Diyala-132 kV is increased and the power losses is decreased.

Techno-economic approach towards reactive power planning ensuring system security on energy transmission network

Abstract This research work proposes a planning strategy pertaining to the techno-economic operation of Indian power systems. The proposed strategy focused on the reactive power (VAr) planning (RPP) subject to the system operating cost minimization ensuring system security. To mitigate the RPP issue, unique meta-heuristic hybridized techniques are adopted to size the optimal parameter settings such as alternator’s reactive power, tap settings of transformers etc. instigated by power flow analysis satisfying all equality and inequality constraints. The controlling variables are optimally determined to solve this non-linear RPP problem. The bottleneck for the installation of static VAr compensators at weak buses is also wiped out by different analytical techniques viz. loss sensitivity, power flow and modal analysis. Two different inter-regional transmission networks prevailing in India are considered to measure the adaptability, efficacy and efficiency of the proposed approach. The results obtained by applying the proposed approach have confirmed that network loss-minimization procedures produce an acceptable solution and reduce the operating cost which is especially important in RPP. The responses of bench mark functions and statistical analysis of the outcomes from both systems allow us to assess the overall efficiency and efficacy of the proposed techno-economic planning approach.

Static Voltage Stability Assessment of the Kenyan Power Network

In recent years, the Kenyan Power Network has witnessed large growths in load demand. Although the increased load demand has somewhat been matched with an increase in transmission and generation capacity, the rate of expansion has not been matched with the rate of increase in load demand due to economic, environmental, and geographical constraints. This has led to the system being prone to instability since it is being operated under stressed conditions. In the recent past, several studies have been carried out on voltage stability analysis and improvement using various conventional methods. However, conventional methods have various limitations in their utilization for voltage stability analysis. One solution to overcome these limitations is to employ a combination of one or more methods so as to get more information and greater degree of accuracy in voltage stability studies. In this paper, a methodology is proposed involving the combination of QV modal analysis, sensitivity analysis (VQ) and power-voltage curves in assessing the static voltage stability analysis taking a case study of the Kenyan Power Network. V-Q sensitivity analysis and QV modal analysis have been used to identify the load regions most susceptible to voltage instability and the corresponding weak buses in the network for various V-Q responses. Reactive power loss sensitivities for branches in the network have been used to determine the critical (weak) lines in the network. Loading margins (LM) and voltage stability margins (VSM) have then been used to determine the proximity to voltage collapse of the voltage weak buses identified by QV modal analysis. The effect of tripping one the critical lines on the voltage weak buses is also investigated. The current high voltage power network under the average peak loading conditions during the year 2019 is considered for the study. The paper also reviews existing voltage stability analysis methods and their limitations.

Multiple Solutions for Optimal PMU Placement Using a Topology-Based Method

This paper presents a novel topology-based optimal PMU placement strategy. The proposed strategy provides the entire feasible solution space which gives the observability of the power system by working on binary connectivity matrix of the system. From the feasible solution space, multiple optimal solutions are obtained. Providing multiple optimal solutions gives flexibility to the system operator to choose one optimal solution which best fits sub-ordinate objectives rather than providing single optimal solution which gives no choice to the operator. This novel strategy has been tested on IEEE 14-bus and IEEE 30-bus system. Multiple optimal solutions are obtained while maintaining observability and maximizing redundancy. For demonstrating the advantage of multiple optimal solutions, minor objectives, such as direct monitoring of generator and weak buses are illustrated. One of the multiple solution which best fits to the minor objectives is chosen as a final optimal solution. The proposed method ensures global optimal solution for various objectives under consideration. In addition, normalized Bus observability index and normalized System observability redundancy index are presented to overcome the drawback of SORI and BOI.

Survey about impact voltage instability and transient stability for a power system with an integrated solar combined cycle plant in Iraq by using ETAP

The Analyses for power systems are more necessary for the designing, operating phase execution control and to make sure safe network operations by sufficient protection project settings. In this article, we have prepared a sufficient scientific survey about the electrical model of a 340 MW integrated solar combined cycle system (ISCCS) located in the Iraqi southern, is developed and simulation by a program called Electrical Transient Analyzer Program (ETAP) and carry out throw this program the load flow, voltage stability and short circuit analyses for this power plant with part of the national grid in Al-Basra city in an industrial region. The effect of voltage instability for the grid on system buses (load buses) of the power system is estimated. By using load flow analysis as a case study by using the Newton-Raphson algorithm, when the load buses operating at down voltage because of instability voltage of the power grid are specified and their voltages are should to improved according to given voltage limitations that are depended on buses criticality with regard to loads. The appliance on-load tap changers of the transformer and reactive power compensation are used to improve steady-state voltage stability for any instability system. The method of the optimal position for capacitor banks placement is meaning the number of capacitor banks is proposed to adding to the weak buses by using the optimal capacitor placement module of ETAP. Energy is actually required for the expansion of our country. To sustain the generation of electric power at an adequate level power system supplies power to different types of loads that are located far away from the generating plants using transmission lines.

Optimum Location of Spvg to Enhance Voltage Stability Using Static Techniques

Solar Photovoltaic Generators (SPVGs) play a great and vital role in providing clean and enough energy to meet power loads. However, SPVGs integration on power systems increase power grid problems. It will lead to different problems including disturbance of the grid, instability of the voltage and swings of the power. The impact of SPVG on the voltage stability of the system is studied in this paper. The best location of SPVG is obtained using three static techniques. Power flow and the Q-V curve techniques are used to identify the weakest buses and test the stability of the system under nominal load condition respectively. On other hand, Continuation Power Flow (CPF) and the Q-V curve techniques are used to identify the weakest buses and test the stability of the system under heavy load condition respectively. The proposed techniques are apllied to the New England 39-bus standard system under various loading conditions. The results reveal that choosing a proper location for the SPVG will improve the voltage stability of the system. In addition, connecting the SPVG at the nearest bus to the weakest bus provides better performance than when it connected to the weakest bus.

Optimal placement of shunt capacitor with VCPI to improve voltage profile using Mi power

ABSTRACTDay to day the importance and usage of electric power is increasing, in order to reach this power demand, generation of power is being increased. But the transmission grid fails to meet the developments in generation, as construction of new transmission lines involve more time than building new generation facilities. So, updating or upgrading the existing facilities will be more beneficial than building new ones. This is achieved by providing proper reactive compensation. This main objective of the paper is placement of shunt capacitor for voltage profile improvement and reactive power compensation. The voltage stability index, called voltage collapse prediction index (VCPI), decides the shunt capacitor placement. This paper deals with placement of shunt capacitor banks to improve voltage at weakest buses. The shunt capacitor banks connected to the system to prevent the low voltages during the high loading conditions. The reactive compensation and reduction of losses and power transfer capability can be increased by placing of shunt capacitor. The proposed technique is validated with load flow analysis on IEEE 14 bus system carry out by Mi-power software. From the results obtained it is verified that the load flow analysis can be easily done with Mi-power which is a fast and robust tool with a powerful GUI to solve. Finally, the voltage profile improvement is verified with the placement of shunt capacitor.