Typical Distribution Feeder Research Articles

Techno-economic assessment of grid-connected residential photovoltaic systems considering overvoltage-induced generation curtailment

Grid-connected residential photovoltaic (PV) systems are continuously installed in worldwide communities, predominantly to reduce electricity bills. However, the rapid growth of distributed PV systems inevitably causes overvoltage in distribution networks. Conventionally, PV curtailment is implemented in a grid-connected inverter to prevent the system from overvoltage. Nevertheless, previous studies have failed to consider PV curtailment caused by overvoltage when conducting techno-economic assessments. Therefore, this study conducts a comprehensive techno-economic assessment of grid-connected residential PV systems, considering overvoltage-induced generation curtailment. A volt-watt curtailment strategy is designed based on a droop characteristic. Simulation studies are conducted using real-world load profiles and electricity tariffs retrieved from the Metropolitan Electricity Authority in Thailand. Furthermore, a typical low-voltage distribution feeder in Bangkok, Thailand, is employed using Thailand’s grid code. Simulation results indicate that the optimal PV size could be reduced by up to 58.33% (depending on the numbers and locations of PV systems) when considering overvoltage-induced generation curtailment, resulting in a profitability reduction of 21.34%. It is concluded that considering overvoltage-induced generation curtailment can accurately determine the PV size, preventing oversizing and overvoltage.

An approach to disparage the blindness of backup protection in grid connected renewable energy sources system by inducing artificial fault current

The renewable energy sources based distributed generation is increasingly penetrating into conventional distribution network . Aside from the technical and economical benefits, distributed generation may incapacitate the sensitivity of backup protection devices , which may face partial blindness in grid-connected, even full blindness in islanded mode of operation and during high impedance faults. This paper proposes a novel stratagem to completely plummet the blindness of backup relay by inducing the artificial fault current. A blindness severity index is developed to induce artificial fault current in a controlled manner according to blindness severity. Two methods are proposed. First, the OCR vulnerable to blindness is provided with an auxiliary current transformer, whose output is tuned in conjunction with blindness severity index and merged with main current transformer’s output to modulate its secondary current responsible for sensitivity. Second, the microprocessor based relay is used and the time current characteristics is modified by augmenting a new variable named as artificial fault current factor to scale the fault current. As, the current is increased by the TCC modification and no external equipment is added here, so named as AFC. To assure that the AFC is induced only in fault event and to prevent mal-functioning of OCR during normal operation, a simple logic is designed using AND gates to fend off trip signal to circuit breaker. The proposed protection scheme is evaluated on typical distribution feeder in Tianjin, China and IEEE-34 standard test benchmark and results show that the blindness of backup PDs is dwindled in a proficient manner.

Distributed Real-Time Multi-Objective Control of a Virtual Power Plant in DC Distribution Systems

Due to the strong coupling between power injections and bus voltages in DC distribution networks, it is impossible to achieve economic dispatch and recover the nominal voltages of all buses, simultaneously. In light of this, a multi-objective optimization-based control model is formulated for the multiple distributed energy resources (DERs) within the DC distribution network to be dispatched as a virtual power plant. A compromise can be made between the economic efficiency and voltage distribution quality by placing different weights on the multiple objectives. To this end, a distributed real-time multi-objective control strategy is proposed. Specifically, facilitated by sequential peer-to-peer communication, the dynamics of the cyber-physical DC distribution system imitate the primal-dual subgradient algorithm to the multi-objective optimization, thus can iteratively converge to its optimal solution. A dynamic weight adjustment mechanism is further designed to bound the bus voltages within a feasible range. This strategy is plug-and-play, privacy-preserving, robust to communication failures, and responsive to change of operating conditions compared to its centralized counterpart. Simulation studies of two typical DC distribution feeders verify the effectiveness of the proposed approach in various scenarios.

Exploitation of Microgrid Flexibility in Distribution System Hosting Prosumers

Increasing the penetration of renewables on prosumers' side brings about operational challenges in the distribution grid due to their variable and uncertain behavior. In fact, these resources have increased the distribution grid net load fluctuation during recent years. In this article, the flexibility-oriented stochastic scheduling of a microgrid is suggested to capture the net load variability at the distribution grid level. In this scheduling, the flexibility limits are set to manage the net load fluctuation at a desirable level for the main grid operator. The uncertainties of load and renewables are considered, and their uncertainties are under control by the risk-averse strategy. Moreover, multiperiod islanding constraints are added to the problem, preparing the microgrid for a resilient response to disturbances. The model is examined on a typical distribution feeder consisting of prosumers and a microgrid. The numerical results are compared for both flexibility-oriented and traditional scheduling of a microgrid at the distribution level. The proposed model reduces the net load ramping of the distribution grid using an efficient dispatch of resources in the microgrid. A sensitivity analysis is also carried out to show the effectiveness of the model.

Modeling and Performance Evaluation of an Electromagnetic Voltage Regulator via Series Compensation

Although there currently exists a wide range of voltage regulators that are commercially available, the search for devices with a simpler physical design remains the focus of research studies. Following this line, an electromagnetic voltage regulator (EVR) arrangement has been proposed. The EVR is constituted of an autotransformer that supplies, via discrete taps, a series transformer that injects voltage for regulating the feeder voltage. Even though its operating principle is shown as being similar to that of other devices on the market, the physical arrangement and operating strategy of EVR show novelties which result in properties such as: economic attractiveness, constructive simplicity, and operational reliability. Moreover, when installing voltage regulators, efficacy studies must be carried out to optimize equipment design. In this context, this paper aims at evaluating the factors that influence the effectiveness of the EVR in restoring voltage variations according to the determinations imposed by regulatory agencies. The ultimate goal of this study is to determine the voltage deviation range that the EVR is able to restore. To achieve this goal, a mathematical modeling of the EVR is given and study cases are computationally carried out to investigate its performance when connected to a typical distribution feeder.

Solar PV Policy, Barriers and Proposed Solution for Technical Barriers in Thailand

This paper presents solar PV history in Thailand consisting of installation target, incentive schemes, procurements and barriers for supporting the coming of solar PV. For the barrier viewpoint, one of the most significant barriers is the technical power system problem; especially, voltage violation and system loss increase when high capacity of solar PV is installed in the system. Therefore, electric utilities usually determine the capacity limitation criterion of solar PV for each electrical feeder which can delay the growth of solar PV installation. Consequently, this paper presents the method to solve this barrier in order to maximize the installation of solar PV in Thailand. The method is based on the construction of typical distribution feeders with various levels of solar PV penetration and locations. The three scenarios based on solar PV locations: clustered near the beginning of feeder, clustered near the middle of feeder, and clustered near the end of feeder are simulated. The considered constraints are voltage limitation and system loss. The modified distribution system is used to test the proposed method which is simulated by DIgSILENT PowerFactory software. The results show that the proposed method provides the solution that can support more solar PV installation than capacity limitation criterion determined by distribution utilities.

Heuristic Method for Fault Location in Distribution Feeders With the Presence of Distributed Generation

This paper presents a fault location method for power distribution networks with the presence of distributed generation (DG) units along their feeders. The proposed fault location method is based on voltage and current phasor quantities, calculated from measurements provided by intelligent electronic devices installed only at the substation bus, and on information about the electrical parameters of the feeders, stored in the utility’s database. It is capable of correctly locating the fault point using detailed models of the feeder’s line sections, information about the impedances of the loads, and the equivalent circuits of the DG units connected to the feeder. The proposed method relies on an optimization process that estimates the fault point using the Pattern Search method. A typical distribution feeder was implemented using EMTP/ATP and test data produced during the simulations were used to evaluate the method’s performance. The simulations considered variations of the fault type and phases involved, variations of the fault resistance, and input data errors. The results indicate that the method is robust and provides a high level of accuracy.

Performance Evaluation of Synchronous and Induction Machines Coupled with Distribution Network

With the rapid increase in energy demand all over the world and great advancements in technology, utilities are more interested in Distributed Generation (DG). Among different sources, synchronous and induction machines are widely used for DG applications. In this paper, a detailed performance evaluation is carried out for induction and synchronous machines in Distributed Generation mode. A typical radial distribution feeder is simulated in Electrical Transient Analyzer Program (ETAP) and the impacts of aforementioned sources are analyzed on DG. On the basis of comparison between sources, some basic technical factors such as voltage profile and electrical power losses are considered. It was found that the most desirable source depends on the characteristics of the distribution network, i.e. the core technical factors that might put constraints on the penetration level of DG.

Enhancing the Capacity of the AC Distribution System Using DC Interlinks—A Step Toward Future DC Grid

The development of distributed generation system and electric vehicles is bound to strain the distribution network. A typical radial distribution feeder suffers from voltage fluctuation and feeder overload in the presence of a large amount of variable renewable generation. This paper presents a concept of enhancing the power handling capacity of distribution networks using dc grid interconnections. Control of both the active and reactive power exchange between the ac feeder and the interconnecting power converter has been proposed for the voltage regulation at the ac feeder terminal. Besides, the dc grid interconnection also allows the introduction of a common storage system that can be shared by the connected ac feeders and the dc grid connection to other renewable energy resources. The increased power handling capacity and improved voltage profile of the ac distribution feeder using the proposed system is shown through time domain simulations on a test system.

Storage Solutions for Power Quality Problems in Cyprus Electricity Distribution Network

In this work, a prediction of the effects of introducing energy storage systems on the network stability of the distribution network of Cyprus and a comparison in terms of cost with a traditional solution is carried out. In particular, for solving possible overvoltage problems, several scenarios of storage units' installation are used and compared with the alternative solution of extra cable connection between the node with the lowest voltage and the node with the highest voltage of the distribution network. For the comparison, a case study of a typical LV distribution feeder in the power system of Cyprus is used. The results indicated that the performance indicator of each solution depends on the type, the size and the position of installation of the storage unit. Also, as more storage units are installed the better the performance indicator and the more attractive is the investment in storage units to solve power quality problems in the distribution network. In the case where the technical requirements in voltage limitations according to distribution regulations are satisfied with one storage unit, the installation of an additional storage unit will only increase the final cost. The best solution, however, still remains the alternative solution of extra cable connection between the node with the lowest voltage and the node with the highest voltage of the distribution network, due to the lower investment costs compared to that of the storage units.

Steady-State Analysis of Maximum Photovoltaic Penetration Levels on Typical Distribution Feeders

This paper presents simulation results for a taxonomy of typical distribution feeders with various levels of photovoltaic (PV) penetration. For each of the 16 feeders simulated, the maximum PV penetration that did not result in a steady-state voltage or current violation is presented for several PV location scenarios: clustered near the feeder source, clustered near the midpoint of the feeder, clustered near the end of the feeder, randomly located, and evenly distributed. In addition, the maximum level of PV is presented for single, large PV systems at each location. Maximum PV penetration was determined by requiring that feeder voltages stay within ANSI Range A and that feeder currents stay within the ranges determined by overcurrent protection devices. Generation ramp rates, protection and coordination, and other factors that may impact maximum PV penetrations are not considered here. Simulations were run in GridLAB-D using hourly time steps over a year with randomized load profiles based on utility data and typical meteorological year weather data. For 86% of the 336 cases simulated, maximum PV penetration was at least 30% of peak load.

Optimization of Recloser Placement to Improve Reliability by Genetic Algorithm

In this paper, a simple method for placing an optimal number of recloser is presented. The algorithm is solved using genetic algorithm as the optimization method. The majority of outage events experienced by customers are due to electrical distribution failures. Increasing network reliability is a necessity in order to reduce interruption events. Distribution network automation can trim down outage events and increase system reliability. Network automation has to be done using optimization approaches. Genetic Algorithm (GA) is a relatively new technique used in power systems optimization problems. Distribution network automation is one of the aspects tackled using GA. However ,the methodologies used to improve the reliability of radial distribution feeders are reviewed. The reliability improvement are demonstrated for typical distribution feeder layouts. determined. The method enjoys the simplicity of conFigure uration, accuracy of the results and reduction of the time consuming. The obtained results also show the applicability of the algorithm

The location of a resistive shunt harmonic impedance along a distribution feeder and its influence on harmonic propagation

Although complete compensation is only possible using true active filters, resistive shunt harmonic impedances (SHI) have been shown to provide a considerable reduction of the harmonic propagation. In this paper, the harmonic mitigation potential of a resistive SHI is discussed concerning its influence on the voltage distortion profile along a typical distribution feeder, with the location of the SHI along the feeder as a parameter. Although the distortion values are dependent on the SHI location, it is shown that the end of the feeder is generally a good location to install the SHI, especially when the power system parameters can vary or are unknown. Calculations are performed on a typical radial distribution feeder. Both the power factor correction capacitors and the non-linear loads are concentrated in single nodes. The linear loads are disconnected to obtain the worst case for the voltage distortion. Also some measurements on a scale model of a typical distribution feeder are done and the experimental results confirm the results obtained from simulations.

A new type of differential feeder protection relay using the Global Positioning System for data synchronization

This paper describes a new technique for sampling synchronisation in a numerical differential feeder protection relay. The protection uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder. The EMTP/ATP power system simulator was used to simulate a typical distribution feeder with faults at various locations. The current signals generated at both ends of feeder were used to evaluate the performance of the protection. These tests were carried out using a protection simulator. The results illustrate the effect of current transformer saturation on the sensitivity and stability of the protection. Finally it is shown that a precisely synchronized differential protection is fast, selective and accurate. On an internal fault it provides a high operating sensitivity, whilst it remains stable on all external faults.

Quadratic programming approach to reactive power optimization on the primary feeders

In this paper we suggest the use of the quadratic programming technique to determine the optimum size and location of shunt capacitors on radial distribution feeders so as to maximize overall savings, including the cost of capacitors. The saving function which is of quadratic form is maximized for a set of linear inequality constraints by using quadratic programming. — For quadratic programming, efficient alogrithms have been developed which can easily be implemented on digital computers. — The approach is illustrated by an application to a typical distribution feeder of 23 kV.