Voltage sag analysis with distributed generation

The use of Distributed Generators (DGs) in distribution system has increased at fast pace in recent times. These DGs can work both as grid connected or standalone mode. Thus when it comes to DG placement, getting the optimal location for its placement and the optimal sizing becomes very important. In this paper, finding the optimal location and optimal size of DGs is dealt keeping active power loss as the objective, considering different load models. A novel method called Backtracking Search Optimization Algorithm is used to find the most significant positions for DG placement. DGs supplying both active and reactive power have been studied. Case studies have been done about the effect of 1, 2 or 3 DGs on the IEEE 69 bus test system for DGs operating at 0.85 pf. on different load models.

A study of a distribution system is presented where the effect of distributed generation (DG) presence is analyzed. The system is typical of a rural, industrial, and low-power (weak) distribution scheme. The concept of specific energy for voltage sag immunity of sensitive equipment (SE) under the new scenario created by the DG presence is applied, especially studying the double magnitude/duration sag that is caused by the change in source impedance due to the response of dissimilar protection devices. The new protection coordination concepts of the not-anymore-radial distribution systems are described. A new methodology for the study of SE behavior under voltage sag when connected to a weak distribution system with DG is proposed.

This paper presents a new framework to analyze the penetration of distributed generation (DG) in distribution systems (DS) based on modified Monte Carlo simulation. The placement and capacity of DG are generated as random variables with probability density functions following the optimality principle of the system. The method of power flows analysis is employed to evaluate the economic and technical aspect of the network both with and without DG sources inside. The results in different scenarios are combined with weighted factors to form the performance indices. The proposed framework is testified in a practical 15 MVA, 22 kV, 48-bus DS in Thai Nguyen, Vietnam. The simulation result shows that many advantages can be achieved with DG such as lower power losses, smaller voltage deviation, over-load reduction, etc. The proposed framework can serve as a platform for DS planning with DG sources in practice.

Distributed generation and the voltage profile on distribution feeders during voltage dips

This paper presents a new method on fault distribution modeling for stochastic prediction study of voltage sags in the distribution system. Two-dimensional stochastic models for fault modeling make it possible to obtain the fault performance for the whole system of interest, which helps obtaining not only sag performance at individual locations but also system sag performance through system indices of voltage sag. By using bivariate normal distribution for fault distribution modeling, the paper estimates the influence of model parameters on system voltage sag performance. The paper also develops the modified SARFIx regarding phase loads that creates better estimation for voltage sag performance for distribution system.

Proliferation of electric demand and congestion in the existing network intensify challenges and problems for researchers and power system planners. Currently, these problems are mostly solved by Distributed Generation (DG). DG is placed near the customer end to meet the load demand economically, hence reducing the existing network burden. This paper attempts to present an overview of technological development carried out in the DG field. Numerous technical constraints must be considered while integrating DG in the system. The improvement in voltage stability, voltage profile, and reduction in power losses are the main benefits posed by DG integration. This paper also highlights the key issues associated with the DG allocation problem, types of DG, and methodologies for optimal DG units allocation.

In this paper controller design for voltage sag ride-through in hybrid fuel cell/battery energy storage distributed power generation system has been presented. As the amount of fuel cell power generation and other distributed generation (DG) with power electronic in the grid grows, it becomes unacceptable to disconnect generating units every time a disturbance occurs, as was common practice in the past. Keeping the VSC on line during unbalanced voltage sags becomes thus a very critical issue. Hence, modeling, controller design, and simulation study of a hybrid distributed generation system are investigated. Based on the classification of unbalanced faults that can occur in the grid, resulting in voltage sags at the bus where the hybrid power system is connected, the maximum current that the converter valves must be bale to withstand is calculated. Simulation results are given to show the overall system performance including active power control and voltage sag ride-through capability of the hybrid distributed generation system.

In electrical systems the most critical disturbance is the interruption of the power service. However, the main concern for many commercial and industrial users is the mal-operation produced by voltage sags. This paper presents a study about performance of a distribution system in presence of voltage sags using a distribution generation (DG) unit and a distribution static compensator (DSTATCOM). The analysis is performed by using a stochastic generation of disturbances method and ATP/EMTP software tool. Several case studies in the IEEE-13 bus test feeder taking to account different DG locations and penetration levels for DG unit are presented. In addition, the relation between the injected DSTATCOM reactive power, the type of sag and the location of affected nodes is considered. Simulations show that for IEEE-13 system the DSTATCOM is the best alternative for sags mitigation. However, the DG unit is an alternative that can be considered in larger distribution systems to reduce the effects of voltage sags.

With recent advances in technology, utilities can expect to see increasing amounts of distributed generation (DG) on their distribution systems. This DG can have positive impacts such as voltage support and deferred capital investments, but can also have negative impacts on protection coordination, voltage regulation, voltage flicker and short circuit levels. Reliability is an area where DG can have both a positive and a negative impact. This paper describes these situations and develops methods to analyze them using predictive reliability assessment tools.

This paper presents a method for optimum allocation of a number of Distributed generation (DG) units in distribution system (DS). The main aim of the present work is to draw attention to some effects of DG's installation on DS. These effects are studied in both normal steady state operation (line power losses) and transient periods (voltage sag losses). As a matter of fact addition of DG to DS decreases grid losses, however it is highly probable that this addition will increase the losses of voltage sags resulting from short circuit (S.C.) on any bus of DS. This makes it important to include the voltage sag losses in optimum allocation problem. The paper applies the conventional particle swarm optimization (PSO) technique with two modifications. The proposed method is applied to the IEEE 14-bus system. Results ascertained contradictive effects of DG installation between line and voltage sag losses which assured the importance of voltage sag consideration in the problem of DG allocation.

This paper discusses the mitigation of voltage sag in distribution systems. Voltage sag often occurs due to a single line-to-ground short circuit fault. The fault has a major impact on load damage in the Pujon feeder line. Voltage sag can be mitigated by using Dynamic Voltage Restorer (DVR). DVR is one type of custom device that is effective in overcoming voltage sag. DVR requires control in regulating voltage recovery on the Pujon line. This research proposes DVR control using Hysteresis combined with ANN to mitigate voltage sag on Pujon line. Simulation results show that the Hysteresis-ANN control is able to recover the load voltage in phase R on average by 97% due to voltage sag that occurs on the Pujon feeder line.

Voltage sag is considered to be the most serious problem of power quality. It is caused by faults in the power system or by the starting of large induction motors. Voltage sag causes about 80% of the power quality problems in power systems. One of the main reasons for voltage sag is short circuit fault, which can be compensated for by a distribution static compensator (DSTATCOM) as an efficient and economical flexible AC transmission system (FACTS) device. In this paper, compensation of this voltage sag using DSTATCOM is reviewed, in which a sliding mode control (SMC) technique is employed. The results of this control system are compared with a P+Resonant control system. It will be shown that this control system is able to compensate the voltage sag over a broader range compared to other common control systems. Simulation results are obtained using PSCAD/EMTDC software and compared to that of a similar method.

Distribution system is the crucial part of the power system which needs to be monitored for quality since it is the last stage in delivering electricity to consumers. The main aim of suppliers is therefore to maintain excellent quality of supply with minimal support at the network level. This includes dealing with issues around voltage regulation and minimization of real power losses on the network which are reflected in a uniform voltage profile through various load points on the feeders. However, with increase in decentralization, Distributed Generation (DG) becomes the focal point of distribution networks and can be used to achieve the above mentioned objectives. DGs are used in this paper to minimize the losses along with an improvement in the voltage profile. The location of these DG units on the network is addressed as an optimization problem using the loss sensitivity index and voltage deviation index. The size of power injected by DG units is obtained with using an intelligent approach that combines Genetic Algorithm (GA) with neural networks. Different cases of DG in terms of real and reactive power injected are considered resulting in an improvement in voltage profile. The loss sensitivity and voltage deviation indices show the best result for the location of DG needed to minimize the power loss along with improvement in voltage regulation. This approach is tested on a 13-bus distribution network with different types of loads placed throughout the feeder.

Due to the continuous increase of distributed generation (DG) penetration into distribution systems, load flow analysis always needs improvement to be more flexible, fast and computationally efficient especially when integrating DG with existing distribution systems. The work in this paper is divided into two parts; in the first part a new algorithm is developed to solve the power flow problem for radial distribution systems with DG modelled as PV bus. This algorithm can be applied for all distribution systems with any number of buses and laterals. In the second part, the developed load flow programme is employed to study the effect of changing the DG location on electric losses and voltage profile. The best location for DG can be determined accordingly to achieve minimum losses with best voltage profile. Typical case studies are implemented and the results obtained are presented and discussed.

Distributed generations (DGs) are widely used to meet electric energy demand in distribution networks. DGs are advantageous compared to the centralized generating units in many ways including reducing power loss, improving voltage profile, enhancing network stability, decreasing pollution, releasing transmission line capacity, and reducing congestion of distribution lines. The size and site of DGs logically influence power loss in distribution networks. The optimal place and capacity of DGs are determined aiming at minimizing power loss in distribution networks. In this article, firefly algorithm (FA) is used for optimum placement of various DGs in distribution networks. Optimum power factor of DGs along with active and reactive powers are obtained in this work. Various DGs of generating/consuming types are considered in the suggested method. Performance analysis of the proposed method has been done on standard IEEE 33 bus system in MATLAB.