Acceptable Voltage Limits Research Articles

A Multiobjective Secondary Control Approach for Optimal Design of DG Droop Characteristic and Control Mode for Autonomous Microgrids

Theoperating condition of a droop-based microgrid is dependent on the distributed generation (DG) droop characteristics. Both primary and secondary controls define the droop characteristic. Previous work dealing with droop-based microgrids overlooked the secondary control region boundary limits while optimizing the droop characteristics as well as the optimal selection of droop type. This article proposes a novel problem formulation that determines the optimal droop type as well as characteristic. Each DG is equipped with two operational control modes namely the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> , one of which is optimally selected to achieve the desired operational objectives. The proposed model is formulated as a multiobjective mixed-integer nonlinear programming, which is incorporated into an optimal power flow framework and tested on a 38-bus distribution system modified to form a microgrid and optimally solved using general algebraic modeling system. A secondary control operating region is defined within which the optimal droops are constrained to maintain all possible operating conditions within the acceptable frequency and voltage limits. Furthermore, a comparative analysis is conducted where the DG droops are optimized with and without considering the proposed secondary control operating region. The dynamic performance of the proposed optimal secondary control is validated using PSCAD/EMTDC.

Optimal Power Systems Restoration Based on Energy Quality and Stability Criteria

Electric power systems (EPS) are exposed to disconnections of their elements, such as transmission lines and generation units, due to meteorological factors or electrical failures. Thus, this research proposes a smart methodology for the re-entry of elements that have been disconnected from the EPS due to unforeseen events. This methodology is based on optimal AC power flows (OPF-AC) which allow verifying the state of variables such as voltage, angular deviation, and power (these variables are monitored in normal and fault conditions). The proposed study considers contingencies N-2, N-3, N-4, and N-5, for which the disconnection of transmission lines and generation units are carried out randomly. The analysis of the EPS after the disconnections of the elements is carried out by means of the contingency index, with which the impact that the disconnections of the elements have on the EPS is verified. In this way, the optimal route is generated to restore the elements that went out of operation, verifying that when the elements re-enter the acceptable limits, voltage and voltage angle are not exceeded. According to the results of the methodology used, it was found that NM contingencies can be applied in the proposed model, in addition to considering stability restrictions, modeled as restrictions on acceptable voltage limits, and a new restriction for the voltage angle between the differences of the bars.

Particle Swarm Optimization for Optimal Allocation of STATCOM on Transmission Network

Static Synchronous Compensator (STATCOM) is one of the members of flexible alternating current transmission systems (FACTS) devices that controls one or more network parameters to increase system power transfer capability. However, it needs be optimally allocated to fully maximize its usage. Allocation of STATCOM simply refers to optimal placement and size of a STATCOM to solve some of the transmission network problems. This paper therefore utilizes particle swarm optimization (PSO) to allocate STATCOM to enhance the system voltage magnitudes and minimize the active power loss. A Matlab programme was developed for the proposed method and applied to IEEE 14 bus network and the results presented. The results showed that the total active power loss was reduced by 6.90%. The voltage magnitudes at buses 7 and 13, which were above the upper voltage limit, were reduced and brought to within acceptable voltage limits and hence improvement in the system voltage profile. Therefore, the optimal allocation of STATCOM improves the efficiency and operation of the network.

Conservation voltage reduction (CVR) via two‐timescale control in unbalanced power distribution systems

Voltage control devices are employed in power distribution systems to reduce the power consumption by operating the system closer to the lower acceptable voltage limits; this technique is called conservation voltage reduction (CVR). The different modes of operation for system's legacy devices (with binary control) and new devices (e.g. smart inverters with continuous control) coupled with variable photovoltaic (PV) generation results in voltage fluctuations which makes it challenging to achieve CVR objective. This paper presents a two-timescale control of feeder's voltage control devices to achieve CVR that includes (1) a centralized controller operating in a slower time-scale to coordinate voltage control devices across the feeder and (2) local controllers operating in a faster timescale to mitigate voltage fluctuations due to PV variability. The centralized controller utilizes a three-phase optimal power flow model to obtain the decision variables for both legacy devices and smart inverters. The local controllers operate smart inverters to minimize voltage fluctuations and restore nodal voltages to their reference values by adjusting the reactive power support. The proposed approach is validated using the IEEE-123 bus (medium-size) and R3-12.47-2 (large-size) feeders. It is demonstrated that the proposed approach is effective in achieving the CVR objective for unbalanced distribution systems.

Elephant herding algorithm-based optimal PI controller for LVRT enhancement of wind energy conversion systems

This article introduces an optimal PI controller optimized by elephant herding algorithm (EHA) to control the grid-tied four-phase 8/6 switched reluctance generator (SRG). This controller is introduced for enhancing the low voltage ride through (LVRT) capability of the grid-tied SRG during faulty conditions that affect the SRG output voltage by regulating the off-delay angle of the generator. These faulty conditions include faults taken place at the point of connection (POC) of the SRG to the grid and wind speed variations. The proposed optimized PI controller regulates the off-delay angle of the generator to keep the voltage at the POC within acceptable limits. Maintaining these acceptable voltage limits during faulty conditions that keeps the generator in connection to the grid and makes the generator complying with the grid codes. Comparison between EHA optimization technique, cuckoo search optimization and particle swarm optimization (PSO) were presented to illustrate the effectiveness of the modern optimization technique used, EHA. An experimental verification of the proposed system is introduced by rewinding the stator and reshaping the rotor of three-phase induction machine to form four-phase, 8/6 SRG. Finite element method (FEM) based on ANSYS software is utilized to get the magnetic characteristics of the reconstructed 8/6 SRG after drawing the 3-D geometrical dimension in AUTOCAD.

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

&lt;p&gt;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.&lt;/p&gt;

Electric Vehicle Charging Coordination on Distribution Network by Using Particle Swarm Optimization and Genetic Algorithm

The Electric Vehiclesbecoming very popular in the recent years. Typically, Electric Vehicles propulsion systems come from one or more electrical motors built inside the vehicles. This motor used electricity as energy combustion method. Due to the limited energy storage capacity, Electric Vehicles need to replenish by plugging into an electrical source. The problems appear during multiple Electric Vehicles perform charging process in an Electric Distribution Network. This process willbe causing line overload and efficiency degradation of Distribution Network. In performance to evaluate the potential of different of charging coordination, a classification has been made. The new coordinated process may consider minimum power losses and acceptable voltage limit. The process also needs to define the optimal uncoordinated and coordinated charging point. Therefore, a simulation-based framework will be performed, that use two algorithms which are Particle Swarm Optimization and Genetic Algorithm.

Development of A Newton Raphson Symmetrical Component Based Technique for Fault Analysis on Nigerian 330 KV Transmission Lines

Fault analysis is one of the basic problems of power system engineering. It plays a significant role in the power system security for supply of stable and economical operations of power systems. This study carried out fault analysis on Nigerian 330 kV, 28 bus system using Newton-Raphson analysis and symmetrical components method to determine the voltage magnitude and fault magnitude in the system. Newton-Raphson method was used to calculate the short circuit pre-fault voltages and currents on power system. This was used to check the weak buses that are out of acceptable voltage limit of ± 10%. After identifying the buses with problems, a three-phase fault on the power network was then calculated using symmetrical component analysis and was simulated using MATLAB to determine the post-fault voltage magnitudes, angles and fault magnitudes of the power network. The pre-fault result showed that buses 13 (New-Haven), 14 (Onitsha) 19 (Jos), 22 (Kano) and 25 (Markurdi) were the buses that fell out of tolerance range of ± 10% and were termed as weak buses. These buses with low voltage values were examined and post-fault calculations were carried out and the results of voltage magnitude and voltage angle were reduced to zeros.The results of pre-fault current magnitude showed that the selected weak buses namely; Makurdi, New-Haven, Kano, Onitsha and Jos have the current magnitude values of 10.4200 p.u, 9.4350 p.u, 8.4501 p.u, 7.5440 p.u and 5.3320 p.u respectively. The results also showed that Makurdi, had the highest fault magnitudes with a value of 25.1006 p.u followed by New-Haven with value of 23.9455, Kano with value of 22.4917, Jos with value of 21.4686 and Onitsha had the least fault magnitude value of 19.8765 p.u under post-fault condition. More so, it was observed that the voltage on the affected buses was reduced however current magnitudes of these buses when fault occurred were excessively high compared to the pre-fault currents.The result confirmed that symmetrical three phase fault is the most severe kind at the transmission lines. The result also revealed the abnormally high magnitude of current that flows through the Nigerian power network to the point of fault. Therefore, the Nigeria power regulator and policies are required to determine the flow of current regularly during faults occurrences in the power system so as to ensuring improvements in the country power sector. The study therefore recommendations that additional lines should be introduced into the network to assist in the strengthening and reduction of long lines to improve the voltage profile of the network, especially New-Haven, Kano, Onitsha and Markurdi lines. The study will assist the power regulators for selection of circuit breakers and rating of protective switchgears installed in power system to enhance the efficiency of the power supply in Nigeria. Keywords: Fault Analysis, Nigerian Power Network, Newton-Raphson, Symmetrical Components, Three-Phase Fault, Voltage Magnitude, Fault Magnitude. DOI : 10.7176/JNSR/9-16-02 Publication date : August 31 st 2019

Menangani Isu Turun Naik Voltan di dalam Sistem Pembahagian Tersambung Penjana Teragih menggunakan Kaedah Faktor Kuasa Tidak Berpusat

Power quality issues has evidently become one of the crucial issues in power system studies. With the integration of distributed generations (DGs) in the power system, the issue of voltage control has become very important as the power system has become dynamic due to the bidirectional power flow. Delivering power while maintaining acceptable voltage limits has become very challenging for the distribution network operators (DNOs). In order to maintain power delivery to the customers whilst maintaining good power quality, the DNOs has undertaken several measures including implementing several voltage control methods to guarantee that the voltage limits in the power system are within permissible limits. This includes the centralized and decentralized voltage control techniques in the system connected with DGs. The DGs are connected to buses 9 and 14 of the test system where these two buses have been identified as the weakest bus. The decentralized voltage control method has also become an acceptable option due to its ease in having limited communication and lower costs in the system. One of the decentralized voltage control method which has been widely used is the power factor control (PFC) method. The IEEE 14 bus distribution test system has been used and integrated with DGs to show the effectiveness of the PFC method in managing the voltage fluctuation issues in the distribution system.

An Improved Asymmetrical Half-Bridge Converter With Self-Driven Synchronous Rectifier for Dimmable LED Lighting

This paper proposes an adaptive feedback gain compensation technique and adaptive feedforward loop control based on analog design for an asymmetrical half-bridge converter without electrolytic capacitor to improve the system dynamic response and the system performance (i.e., low flickering and low ripple) for dimmable high-brightness light-emitting diode (LED) applications. In addition, an improved driving circuit of self-driven synchronous rectification (SR) is proposed for switching loss reduction at the secondary of the transformer. The control circuit is designed such that the SR metal–oxide–semiconductor field-effect transistor switch operates under zero-voltage switching (ZVS) mode while the driving signals are maintained within the acceptable voltage limits under duty cycle variations of the LED dimming applications. Simulation and experimental results obtained from a 60-W hardware prototype have confirmed the validity of the proposed method, where the settling time of the output current has been improved by 90% and the ripple of the output current has been reduced to less than 4% under rated current. The SR switches operate under ZVS condition throughout all operating regions where the maximum efficiency at 96.4% has been achieved.

Maximum Loadability Identification Using Self-Tuning Algorithm Considering Voltage Limit

Due to the complexity of power system nowadays, voltage limit has become a concerned issue. This phenomenon attracted numerous studies in finding the ultimate solution. This paper presents the development of self-tuning technique for identifying maximum loadability for selected buses in a power system network. The algorithm is able to perform fast process in consideration of the voltage limit between 0.9 p.u. to 1.05 p.u. as the acceptable voltage limit in power system community. The proposed concept is conducted for single and multi-load increment; executed on IEEE 14-Bus RTS and IEEE 26-Bus RTS. The proposed technique is feasible for larger transmission system implementation, which in turn avoid computation burden to power system operators.

A Comparative Study on Optimal Conductor Selection for Radial Distribution Network using Conventional and Genetic Algorithm Approach

paper presents the methodology for the selection of optimal conductors, in radial distribution systems by comparative study of the results obtained by conventional or analytical method and Genetic algorithm method (GA).The objective is to minimize the real and reactive power losses in the system and to maximize the total saving in cost of conducting material while maintaining the acceptable voltage levels. The conductor, which is determined by conventional method will satisfy not only the maximum current carrying capacity and maintain acceptable voltage limits. It is observed that the number of computations is more in conventional method than Genetic Algorithm. The proposed method is tested on 13 bus of Andhra Pradesh southern power Distribution Company limited.

Determination of optimal sending voltage profile in distribution systems with distributed generators

AbstractSending voltage profile of distribution feeder is controlled by changing a tap of distribution transformer. In a distribution network with distributed generators, for reasons of effect of reversed flows from them and existence of a great number of sending voltage profile candidates, it is not easy to control sending voltage profile within the acceptable voltage limit. In this paper, in order to determine the optical sending voltage profile of distribution transformer in a distribution network with distributed generators, the authors propose a new method to determine the optimal sending voltage profile so as to minimize the total number of tap position's change per day under constraints of acceptable voltage limit. In the proposed method, after calculating acceptable range of three‐phase voltage of distribution feeder, the optimal profile of tap position within the calculated acceptable voltage range is determined among these candidates by using reduced ordered binary decision diagram (ROBDD) which is an efficient enumeration algorithm. In order to check the validity of the proposed method, numerical simulations are carried out for a distribution network model with a distributed generator. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 16–24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20393

Determination Method for Optimal Sending Voltage Profile in Distribution System with Distributed Generators

Sending voltage profile of distribution feeder is controlled by changing a tap of distribution transformer. In a distribution network with distributed generators, for reasons of effect of reversed flows from them and existence of a great number of sending voltage profile candidates, it is not easy to control sending voltage profile within the acceptable voltage limit. In this paper, in order to determine the optimal sending voltage profile of distribution transformer in a distribution network with distributed generators, the authors propose a new method to determine the optimal sending voltage profile so as to minimize total number of tap position's change per day under constraints of acceptable voltage limit. In the proposed method, after calculating acceptable range of three phase voltage of distribution feeder, the optimal profile of tap position within the calculated acceptable voltage range is determined among these candidates by using reduced ordered binary decision diagram (ROBDD) which is an efficient enumeration algorithm. In order to check the validity of the proposed method, numerical simulations are carried out for a distribution network model with a distributed generator.

Step and touch voltage – an update for 2004

Hazardous step and touch voltages arise in a variety of high voltage electrical installations, and there are a number of different industry publications which publish acceptable step and touch voltage limits. This paper sets out the derivation of step and touch voltage limits based on the work of Dalziel and Biegelmeier and Lee, and AS/NZS 60479.1:2002. It then provides an outline of the different step and touch voltage limits used in current Australian guidelines, handbooks, and standards. There is a lack of consistent information available to utilities and designers to establish reliable step and touch voltage limits for different installations. This places the utilities and designers in a position of risk from litigation due to personal injury as the engineering models and guidelines in current use may not provide a robust defence. As a key step in risk management, this paper proposes further research to establish consistent and reliable step and touch voltage limits based on body shock currents, body impedance, and probability.