Robert F. Arritt

Distribution system analysis and the future Smart Grid

The “smart grid” refers to various efforts to modernize the power grid through the application of alternate sources of energy and intelligent devices. The present national interest in smart grid applications has generated many questions concerning the role of distribution engineering in the future. What features do utility engineers need in distribution system analysis tools to support the future smart grid? This paper will discuss some relevant Electric Power Research Institute research in this area that focuses on selected issues related to smart grid analysis relevant to rural utilities. The essential characteristics of distribution system analysis tools to support analysis of these issues are discussed.

Distribution System Analysis to support the Smart Grid

The “Smart Grid” refers to various efforts to modernize the power grid through the application of intelligent devices. This paper describes current thinking by members of the Distribution System Analysis Subcommittee (DSA SC) on how distribution system analysis might evolve to support the Smart Grid. Various issues related to Smart Grid and distribution system analysis are identified. The essential characteristics of distribution system analysis tools to support these issues are discussed. Relevant activities of the DSA SC are described.

Distributed generation interconnection transformer and grounding selection

The interconnection of distributed generation (DG) into the power distribution system creates many challenges for utilities. Many of these challenges are related to the type of interconnection transformer (or lack thereof) and consequently the grounding used for the DG interconnection. There remains confusion about the various transformer types for DG interfacing. This is a critical point because the selection of the correct interface with the local utility will simplify feasibility studies; therefore, decreasing the overall cost of the DG interconnect investigation to benefit all. This paper discusses the advantages and disadvantages of different interconnecting transformers. Neutral reactor sizing for grounding transformer connections is discussed.

Roadmap for the IEEE PES test feeders

The Distribution System Analysis Subcommittee (DSAS) of the IEEE PES Power System Analysis, Computing, and Economics Committee has been developing benchmarks for distribution system analysis tools. A number of test cases have already been developed may be easily downloaded on the Internet. Other test cases have been requested. This paper describes the purpose and planned direction for these test cases in the near future. Participation from the power industry is solicited.

Effect of line modeling methods on neutral-to-earth voltage analysis of multi-grounded distribution feeders

Accurate determination of neutral-to-earth voltages (NEV) in multi-grounded distribution circuits can be quite important, particularly in systems where loads are highly unbalanced or have considerable triplen harmonic current content. Some commercially-available and open source software are capable of representing distribution systems in adequate detail for performing NEV analysis. However, results can vary among programs depending on how the distribution line and associated grounding systems are modeled. This paper describes ways to model distribution lines and grounding systems to perform NEV analysis focusing on the earth return model. A simple test feeder is used to show how different distribution line and grounding system models affect NEV analysis.

Review of the Impacts of Distributed Generation on Distribution Protection

Distribution protection practices have undergone many changes in recent years due to higher penetration of distributed generation (DG) and advanced control systems on distribution systems. To help utilities prepare to meet these evolving challenges it is very useful to learn from the practices and experiences of others in the industry. Accordingly, EPRI has conducted a review of participating utilities to gather information on distribution protection practices. The ultimate goal of this review was to learn about existing protection practices and determine what lessons have been learned from experiences with protection of distribution systems with DG.

Techniques for analyzing distribution system efficiency alternatives

The concept of reducing distribution system energy losses is not new; however, advancements in data availability and tools for distribution system analysis have made it more practical to accurately compute distribution system energy savings. Distribution system losses are relatively low compared to the total load demand and there are uncertainties in system parameters that might be included in the model. Improvements in losses are even a smaller portion of the total demand. It is quite a challenge to the analyst and the analysis tools to model the system in sufficient detail to accurately quantify the possible savings. This panel presentation describes modeling techniques employed in a multi-utility collaborative effort to improve the efficiency of power distribution systems.

Summary of modeling results for distribution efficiency case studies

The EPRI Green Circuits project was a collaborative effort of 22 utilities with the main objective of evaluating ways to improve distribution efficiency. For this evaluation, 66 circuit case studies were used. Each circuit was modeled in detail from the substation to each customers meter. Nearly all of the circuit models were augmented with historical circuit-measurement data that allowed for hourly-resolution simulation of the operation of the circuit for actual load patterns for each hour in a calendar year (8760 hours). All sources of losses through both daily and seasonal load changes were found with these circuit models. This paper provides a summary of the collective results from 66 circuits modeled.

Real world ASD interference case study with modeled solutions

The installation of adjustable speed drives (ASDs) has been known to cause many types of radiated and conducted emissions-related electromagnetic interference (EMI) problems. Solutions to resolve these problems are often not straightforward and involve the correction application of filtering and shielding devices. The process of identifying effective solutions is also not straightforward. This paper describes a real-world case study where the use of several high horsepower ASDs caused EMI problems with a cable tester in an industrial plant. Included are the approaches for investigating the problem and mitigating the problem. It is shown that the correction application of an isolation transformer combined with the application of a custom power-line filter designed for mitigation of ASD-related conducted emissions resolved the problem. Modeling is also used to show the effects of adding a shield and a filter on the motor drive cables, and then a ground noise filter between the ASD system ground and the chassis ground.