Radial Feeder Research Articles

Optimal Placement of D-STATCOMs into the Radial Distribution Networks in the Presence of Distributed Generations

This paper proposes a combination of Discrete Imperialistic Competition and Nelder-Mead algorithms to solve D-STATCOMs placement optimization problem. It is assumed that optimal number, locations and sizes of D-STATCOMs are determined in radial distribution network while Distributed Generations are previously installed in it. Indeed, we focus on voltage control and concept of reactive power management in annual scheduling time interval. Objective function is defined in terms of network active power losses and voltage stability characteristic at different load levels by appropriate weighting factors. Voltage Stability Index (VSI) is applied to identify the weak buses in radial distribution network. To validate performance and effectiveness of proposed DICA-NM hybrid algorithm, simulation studies are applied on the 30-bus IEEE radial distribution test feeder. Finally, numerical results for some important network variables have been compared in three different case studies.

An Active Filter With Resonant Current Control to Suppress Harmonic Resonance in a Distribution Power System

A shunt active filter operated as a harmonic conductance is able to suppress a harmonic resonance in the distribution power system. However, due to the inherent phase-lagging in digital signal processing, the active filter really behaves as a harmonic admittance instead of conductance. This may induce unintentional harmonic amplification at other locations in the feeder when starting the active filter, which is similar to the so-called whack-a-mole phenomenon. This paper presents an active filter with resonant current control to suppress a harmonic resonance. The current control is realized by parallel-connected bandpass filters tuned at harmonic frequencies to ensure that the active filter functions as an approximately pure conductance. The conductance at dominant harmonic frequencies can be separately and dynamically adjusted to guarantee the damping performance. In addition, in order to address the harmonic resonance, the line distributed-parameter model of a radial feeder is developed considering harmonic damping by variable conductance and admittance, respectively. Simulation results show that the active filter with the resonant control provides a better damping performance compared with other control methods. A lab-scale prototype circuit rated at 220 V/20 kVA also validates the effectiveness of the proposed method.

Multivariate Statistics and Supervised Learning for Predictive Detection of Unintentional Islanding in Grid-Tied Solar PV Systems

Integration of solar photovoltaic (PV) generation with power distribution networks leads to many operational challenges and complexities. Unintentional islanding is one of them which is of rising concern given the steady increase in grid-connected PV power. This paper builds up on an exploratory study of unintentional islanding on a modeled radial feeder having large PV penetration. Dynamic simulations, also run in real time, resulted in exploration of unique potential causes of creation of accidental islands. The resulting voltage and current data underwent dimensionality reduction using principal component analysis (PCA) which formed the basis for the application ofQstatistic control charts for detecting the anomalous currents that could island the system. For reducing the false alarm rate of anomaly detection, Kullback-Leibler (K-L) divergence was applied on the principal component projections which concluded thatQstatistic based approach alone is not reliable for detection of the symptoms liable to cause unintentional islanding. The obtained data was labeled and aK-nearest neighbor (K-NN) binomial classifier was then trained for identification and classification of potential islanding precursors from other power system transients. The three-phase short-circuit fault case was successfully identified as statistically different from islanding symptoms.

Modeling and Simulation of the Protection of Distribution Feeders in ATP

This article presents the modeling and simulation in the ATP (Alternative Transients Program)/MODELS of devices used in overcurrent protection of distribution networks such as reclosers , sectionalisers , fuses , digital relays and current transformers. A radial feeder with 63 buses was used in the study case. Numerous tests of short - circuits involving single-phase, two phases and three phases at various points of the feeder, were performed, with the purpose of validating the developed models and check the performance of the protection system. The results show the advantages of this type of modeling through which it is possible to evaluate the behavior of the power system against the operation of the protection and the protection front to diverse operating situations to which it is subjected. This study may contribute to the solution of problems of adjustment, coordination and analysis of the behavior of the distribution network using it for more elaborate models of power system components that are available in the ATP software.

A Transformerless Back-To-Back (BTB) System Using Modular Multilevel Cascade Converters For Power Distribution Systems

This paper presents an intensive discussion on a transformerless back-to-back (BTB) system using modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). It is expected to be applied to a power distribution system with many distributed power generators. This paper designs, constructs, and tests a three-phase 200-V, 10-kW DSCC-based BTB system installed on a 200-V, 40-kW power distribution simulator consisting of two radial feeders. Experimental results show that the BTB system can mitigate power-flow imbalance between the two feeders. Moreover, the zero-sequence current circulating between the two feeders can be suppressed to be as small as 10 mA ( $0.02\%$ ) in rms by connecting a common-mode choke to the common dc link of the BTB system.

The Simulation of Loop Flow in Radial Distribution Analysis Programs

Distribution systems are typically composed of radial feeders. Radial means that there is only one path of current flow to each of the loads on the feeder. There are times when it becomes necessary to form a loop in a feeder by closing switches. This may be because of an outage or a new load that will cause the radial current to exceed the conductor current rating or violate the American National Standards Institute voltage requirement. This paper will present a method for simulating the loop flow using an injection current technique. A simple single-phase circuit is used to demonstrate the steps in the simulation. Following that, the IEEE 13 bus test feeder will be studied as it is right now, followed by the addition of a new three-phase load at one bus and a new single-phase load added at another bus. Both of these loads are going to require the addition of new lines and the capability of operating the feeder with one or two closed loops. The process for simulating the closed loops will be presented.

Reliability Evaluation of Distribution Structures Considering the Presence of False Trips

This paper presents a method for modeling the different modes of failures in a substation and feeder architecture along with updating the possible false tripping scenarios in it. A traditional approach to collectively assess the failure modes using reliability block diagram is reviewed, and the method is updated to count in the unaccounted false tripping scenarios. A generalizable radial feeder branching structure is adopted and the effect of total feeder length and number of feeders from each busbar is examined and modeled with the help of the updated reliability block diagram. The modeled trends are also studied from real-world substation architectures. Thus, the analysis attains an improved estimation of the complex hidden failure probabilities combining theoretical and practical models.

Performance Analysis of Unbalance Radial Feeder with Time Varying Composite Load

The focus of this paper is to present performance indices for unbalance radial feeder having different characteristic and composition of time varying static ZIP load models. These provide a framework for benchmarking of distribution automation projects. 15 minutes characteristics time interval for load flow and load modeling are considered to meet smart grid implementation criterion. A forward-backward sweep method is employed for load flow solution. Developed performance indices were illustrated on modified IEEE 37 node test feeder. Performance indices are useful for analysis, operational, planning and integration of stochastic renewable sources.

Enel Distribuzione projects for renewable energy sources integration in distribution grid

The integration of the dispersed generation, based on constantly increasing renewable energy sources, is one of the biggest challenges of the modern distribution system operator.Enel Distribuzione, that operate the 85% of the Italian distribution grid with 33 million customers, connected more than 25GW of dispersed generations, mainly based on renewable energy sources, in Italy up to 2013; these numbers are most impressive taking into account that the consumption peak for medium voltage and low voltage distribution networks was 40GW during the 2007 (the period before the economical crisis and with very small dispersed generation connected).The original design of Enel Distribuzione networks is radial and does not consider interconnection of any generation with significant size. In a radial feeder, the power flows unidirectionally from a single source to the loads. The penetration of dispersed generation into the feeder can cause a flow reversal. This flow reversal violates the concept of “radial design” and has a significant impact on the operation of the feeder and, in particular, on the protection systems and on the voltage regulation.In this scenery, Enel Distribuzione implemented and is implementing several large area demonstrations to test innovative smart grid technologies, in particular for dispersed generation integration. In this paper, two of these projects are presented focusing on the innovative solutions for voltage regulation and dispersed generation dispatching.

Voltage balancing in low‐voltage radial feeders using Scott transformers

Increasing use of heat pumps, micro-generation, electric vehicles and energy-saving technologies is expected to cause severe voltage imbalance on low-voltage (LV) radial feeders and deteriorate the power quality seen by single-phase (1Φ) and three-phase (3Φ) LV connected consumers. To solve this problem, a Scott transformer-based balancing technique is used to convert an unbalanced 3Φ supply into a balanced 3Φ supply at either one point on an LV radial feeder or a 3Φ load supply point. Moreover, by replacing the traditional methods of increasing LV cable cross-sections to solve voltage imbalance; or future solutions such as automatic network reconfiguration, the economic cost of operating and upgrading a ‘stressed’ LV feeder can be minimised. A computer simulation study, in which the proposed method is used to balance a typical UK LV network, with varying levels of imbalance, was carried out. Furthermore, a ‘small-scale’ physical voltage balancing system based on the proposed method was constructed and tested in the laboratory. The results obtained from various simulation and experimental scenarios demonstrated that the proposed method can continuously maintain a balanced 3Φ supply by compensating for phase-related voltage dips and surges resulting from variations in 1Φ connected loads.

Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems

High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.

Reactive power consumption in photovoltaic inverters: a novel configuration for voltage regulation in low‐voltage radial feeders with no need for central control

AbstractHigh photovoltaic (PV) system generation in low‐voltage feeders can cause voltage rise especially in low demand conditions. The conventional way of coping with voltage violation is disconnection of the PV systems or curtailment of the generated power. To address this issue, a novel configuration for voltage management in a radial feeder via regulated reactive power capability in PV inverters is presented. The novelty of the proposed configuration is based on the fact that all the PV inverters with the ability to consume reactive power are involved in voltage regulation without being centrally controlled. In order to apply the configuration, a reference voltage is initially estimated for each PV system, and the PV inverters are calibrated accordingly. These settings depend on the feeder topology and can be calculated by the distribution network operator with a simple power flow modelling tool. Finally, this paper presents a sensitivity analysis in order to examine how reactive power consumption in a single inverter influences PV penetration and inverter sizing at various PV topologies along the feeder. Copyright © 2014 John Wiley & Sons, Ltd.

A New Model Applied to the Distribution System Planning for Competitive Electricity Markets

Recently, the restructuring of electricity market and the development of technology have been enhancing the application of distributed generators (DGs) and renewable energy resources. Hence, the planning of distribution systems (PDS) for competitive electricity markets (CEMs) has encountered impacts which need to be investigated. This paper proposes a novel approach for optimazing distribution system planning in CEMs with the presence of DGs. The proposed model can determine equipment sizing and timeframe required for upgrading power network in order for utilities to purchase electric energy from electricity markets. Besides, the problems of DG system development (Optimal DG displacement, sizing, technology selection and installation period) in distribution planning to meet the demand growth will be solved. The model uses the objective function that minimizes the total cost of network (feeders and transformers) upgrading, new DGs installation, distribution systems operating, and electric energy purchasing from CEMs. The proposed model is tested using a 33 bus 22 kV radial feeder. The calculation is programmed in GAMS environment.

A methodology to calculate maximum generation capacity in low voltage distribution feeders

The aim of this article is to present an easily applicable methodology to calculate maximum distributed generation (DG) capacity in radial low-voltage feeders. The methodology indicates the highest capacity that can be installed at a fixed point in the feeder for which the voltage is kept within the permissible limits in critical scenarios, i.e. high generation and low load. The concept is based on the main findings of previous studies identifying the points of connections where the voltage may be exceeded. The provisional voltage profile of a line is strongly related to the topology of DGs along the line. The methodology can be applied in any radial feeder with or without existing DG installations.

Unbalanced Radial Distribution System Power Loss Reduction by Optimal Distributed Generator Sizing and Location Using Differential Evolution Technique

Distributed energy sources cadge today’s demand. The distributed generation is one of the alternative methods for reducing the gap between power generation and demand. The distributed generation confirms the efficacy of meeting escalating demand when placed at appropriate location with proper size. The objective of this work is to track the suitable place with appropriate size of the Distributed Generators to be installed in an unbalanced radial distribution test system to minimize the power losses while satisfying the operational constraints like rms value of bus voltage limit and the thermal limits of radial feeder lines. The proper location for placing the Distributed Generators is identified by estimating voltage stability index. A meta-heuristic approach based on Differential Evolution algorithm is utilized to get the optimal sizing of Distributed Generation. The proposed algorithm is implemented on the modified IEEE 37 bus unbalanced radial distribution network.

English

This paper presents a set of analysis tools for self learning for radial power system protection training (Bouhenna 2010). It automates a radial feeder for an overcurrent protection that would include fault calculations, fuse-fuse co-ordination, current transformer, relay-relay and fuse-relay co-ordination, directional overcurrent protection, ground fault protection, automatic recloser and sectionalizer. The software explains the function of all these protective elements and provides the students with the skills and knowledge necessary to understand and comprehend radial power system protection. Key words: Set of analysis tools, radial power system protection, fault calculations, co-ordination, protective elements.

Voltage stability analysis of unbalanced distribution systems using backward/forward sweep load‐flow analysis method with secant predictor

This study presents a new method for tracing voltage power curves in unbalanced radial distribution power systems. The proposed method starts with the base case loading conditions and leading to the maximum loading point (MLP) whereas no ill-conditioning problems were detected. The calculation is performed by first-order polynomial secant predictor and the solution is corrected using the backward/forward radial power-flow method. Adaptive stepwise control is implemented to improve the overall solution process and reduce the number of the calculated points along the traced curve. The results calculated using the developed method are for both a 33-bus radial feeder and the unbalanced IEEE 13-node and IEEE123-node feeders. The results show that the developed method accurately traces the voltage power curves up to MLP. Comprehensive analysis on unbalanced scenarios shows that load unbalance greatly affects the stability limit of the study system.

Reliability Indices Evaluation of a Real Time Rural Radial Distribution Feeder

Estimation of the customer oriented, load and energy orientated indices are very helpful for assess the harshness of the system failure in a radial distribution feeder for the future purpose of prediction analysis. It can be assessed by means past performance of an arrangement. In reality, at the present time, they are extensively used for future presentation. These indices are used in the distribution system operation and planning studies. Distribution system reliability evaluation is a measure of continuity and quality of power supply to the consumers, which mainly depends on interruption profile, based on system topology and component reliability data. The paper primarily presents the real time radial feeder; the reliability is calculated in two stages. One by insertion capacitor at weak voltage nodes for augmentation of voltage profiles and plummeting the total system losses. Second by placing protective apparatus (isolators) in the feeder and enhance the reliability indices. Paper attempts a successful technique for real time valuation of distribution load flow solutions with a goal of obtaining voltage profiles and total system losses. The voltage profiles improvement and reducing losses by placing capacitors at weak voltage profile nodes using Particle Swarm Optimization (PSO) technique. Reliability Indices are premeditated for the existing feeder prior to and after placement of isolator. Load diversity factor is used for analysis of load data for real time system. The paper presents a topological characteristic of a radial distribution feeder have been fully utilized to make the direct load flow solution is possible. This paper also presents an approach that determines optimal location and size of capacitors on existing radial distribution systems to improve the voltage profiles and reduce the active power loss. The performance of the method was investigated on an 11kV real time rural PantramPalli radial distribution feeder as system of case study. A matlab program was developed and results are presented.

Sensitivity analysis to connect distributed generation

One of the alternatives to reduce costs in a power system is the application of distributed generation (DG). Although inherent flexibilities of DG, the point of connection must be carefully chosen in order to avoid any hazardous impact. Normally, this choice is based on loss minimization, improvement of the voltage profile and reduction of the power flows through the lines. The search field of this problem is vast. In order to diminish it, this article assumes that only some buses of the network are candidates to the connection. Thus, one of the main objectives of this work is the proposition of a sensitivity analysis that indicates the best buses to realize the connection. Due to peculiarities of this proposed analysis, the voltage phasor is represented by the rectangular form. To test it, a conventional allocation’s methodology is implemented and solved using genetic algorithms (GA) together with an optimal power flow (OPF). A purely radial feeder of one distribution company in Brazil, with 2678 buses and a typical network of 70 buses are chosen to present the results of the methodology.

Implementation of three-phase transformer model in radial load-flow analysis

This paper presents an efficient approach for developing three-phase transformer admittance matrices in the radial power-flow analysis. The proposed transformer model overcomes the singularity problem of the nodal admittance submatrices of ungrounded transformer configurations. This has been achieved by applying symmetrical components modeling. The classical (6×6) transformer nodal admittance matrix written in phase components is converted to sequence components instead of the (3×3) admittance submatrices. In this model, the phase shifts accompanied with special transformer connections are included in the radial power-flow solution process without any convergence problems. The final model of the transformer is represented by a generalized power-flow equation written in phase components. The developed equation is applicable for all transformer connections. The transformer model is integrated into the radial power-flow and tested using the IEEE radial feeders. The results have shown that the developed transformer model is very efficient and the radial power-flow has robust convergence characteristics.