Roger C. Dugan

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 Feeder Harmonic Study Methodology

The procedures for performing harmonic studies are becoming more important to distribution engineering as more harmonic-producing loads are added to distribution feeders. This paper summarizes the methodology used to perform these studies and describes some of the tools used in the analysis. A typical example illustrates the methodology for a feeder that has a telephone interference problem.

Simulation of Arc Furnace Power Systems

An electronic arc model has been developed which simplifies the study of harmonic phenomena in are furnace power systems on a transient network analyzer (TNA). The model helps insure the proper magnitude and phase relationship of the harmonies at each loading condition. The simulation procedures and arc model characteristics are described. Also, some examples of typical study results are given.

Digital Simulation of Distribution System Frequency-REsponse Characteristics

A new digital computer program developed for harmonic analysis of multi-phase networks is described. The program-the Distribution Feeder Harmonic Analysis (DFHA) Program-is designed to conveniently model distribution systems to determine frequency-response characteristics. Results of simulations performed for two different distribution systems are compared with actual harmonic measurements on the systems. Simulation accuracy is evaluated and guidelines are presented for modeling a distribution system and performing the digital harmonic analysis.

Validated techniques for modeling shell-form EHV transformers

It is very common for power transformers to have at least one dominant natural frequency in the 8-to 20-kHz range and minor resonances at a multitude of other frequencies. It is important for the transformer designer to known how a transformer will respond to impulses that may excite these natural frequencies and lead to conditions which are commonly referred to as part-winding resonances in the literature. The utility engineer applying the transformer may also have a need to be aware of the transformer characteristics because there may be transient events on the power system that would excite the natural frequencies. The phenomenon of part-winding resonances has been recognized for many years. However, transformer failures attributed to part-winding resonance continue to occur. The problem persists for mainly two reasons: 1. Lack of validated models and adequate computer tools for designers. 2. System conditions that generate oscillatory transients of a frequency to which the transformer is vulnerable. This paper primarily addresses the progress made toward providing designers with validated models and computer tools. However, the models should also be of benefit to systems analysts to address the latter issue. The power system analyst would use the models, or the results of modeling, to identify potentially dangerous system conditions. Up to the time of the efforts reported here, determining the model inductances and capacitances was largely an art. The task was delegated to a few specialists, the number of which has been dramatically reduced by the economic downturn in the power transformer industry.

Harmonics And Reactive Power From Line-Commutated Inverters In Propposed Photovoltaic Subdivision

This paper describes how one hundred 6.6 kW line-commutated inverters in a proposed photovoltaic subdivision will affect the 10 MVA distribution feeder to which the inverters are connected. Voltage distortion and reactive power correction were studied using a special simulation computer program. The worst-case level of voltage total harmonic distortion is 6.2%, and by setting capacitor switching practices carefully it should be possible to keep voltage THD around 2-3%. The harmonic distortion is greatly affected by the placement of capacitors on the system.

The Personal Scientific Computing Environment: A New Approach to Power Industry Computer Applications

Another revolution is occurring in computer hardware that will affect computer users in the power industry. The first generation of powerful personal1 computers for scientific applications is now on the market. These computers have several advantages over conventional computers: very fast graphics, uniform response time, and a visually-oriente user environment that increases user productivity dramatically. These advantages are the result of having a very powerful processor devoted to a single users needs.

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.

Overvoltage Considerations for Interconnecting Dispersed Generators with Wye-Grounded Distribution Feeders

A dispersed generator on a distribution system can continue to energize the feeder during fault disturbances. In particular, when a permanent single-line-to-ground (SLG) fault exists, generators connected through delta-delta transformers tend to force the unfaulted phase voltage to 1.73 pu. Because of this, some utilities require that the customer generator be connected through an effectively grounded source. Other utilities are not concerned with the overvoltages and do not use effectively grounded sources on a distribution feeder because they may defeat the coordination schemes that use fast tripping to protect fuses on temporary SLG faults. In some cases, providing a solidly grounded source can be prohibitively expensive for some dispersed-generation systems.

Distribution and wind (review of Distribution System Modeling and Analysis by W. H. Kersting; 2006) [book review]

Nearly every chapter in this book has been updated in this second edition. Each step of performing an analysis is meticulously spelled out so there is no question in the mind of the reader on how to repeat the process. The book includes classroom problems and numerous examples, making it quite appropriate for teaching distribution system analysis. All of the examples and data tables reflect North American practice. The book should be useful for both classroom use and as a reference for practitioners for many years to come. It is destined to become a classic.