By Francis Luces, Ric Austria, Cherry Bautista, Ted Garcia

The undesired outages of generating units during the July 1996 Outages in the Western Interconnection and the August 2003 blackout in the Eastern Interconnection have resulted in updates to reliability standards which secure, improve, and optimize generator response during power system disturbances. The North American Electric Reliability Corporation (NERC) has recently issued Standard PRC-019-2 which specifies reporting and review standards for generator protection coordination.  Because the skill requirements to conduct the review are not normally included in plant operations, outside experts are brought in that have a knowledge of what may be available in terms of information and data at the plant, the technical knowledge to conduct the coordination assessment and the experience to identify needs and deficiencies that are critical to presenting a credible review report.

In recent work, Pterra, acting as an external resource, developed approaches to conducting the review for compliance with PRC-019-2 for several legacy power plants.  Such power plants have been in operation for many years, but may have changed ownership at least once, and where test results and data may not be readily available.  This article discusses the general review approach, and applies this to a sample a 230-MVA Steam Turbine Generator Unit in a combined-cycle power station.

In recent work performed by Pterra, the issue of ground fault overvoltage (GFOV) was raised in relation to integration of distributed generation (DG).  In particular, can inverter-based photovoltaic systems, connected in distribution feeders, induce GFOV on the high -side of the substation transformer?  And if so, under what conditions could this occur? Pterra was engaged to conduct a research study by NYSERDA (the New York State Energy Research and Development Authority) to answer these very questions.

This topic was presented at the PSCAD Conference held October 6-7, 2016 in Houston, Texas.

Overview: A 200 MW DFIG wind farm is experiencing nuisance tripping.  These occur during switching of power factor correction cap banks comprising of 4×12 MVAR connected to the farm’s 34.5 KV collector buses.  Trip signals recorded by WTGs indicate power quality issues.  Harmonic distortion study of the Project did not indicate potential violations.

by Francis Luces

Introduction                                                               

For developers of power plants, one of the important factors to consider is where and how to interconnect a plant to an existing transmission network in order to reliably deliver its full output. For conventional power plants (i.e. coal, oil, natural gas, etc.), the availability of fuel supply and environmental permitting are the main considerations for siting. In the case of solar photovoltaic (PV) projects, given the availability of land area for mounting solar panels and sufficient solar irradiance, the point of interconnection (POI) to the grid can be the determining factor for siting. An assessment of the thermal capacity at potential POIs provides an effective screen for potential sites. Using transmission capacity injection analysis, developers can swiftly determine the capability of the existing network to support additional power from a new source such as a PV project. With this type of analysis, solar power project developers can know fairly early in the development process if the selected site and POI can support the plant’s output.

Pterra has been a fan of the General Electric PSLF transmission planning software product almost ever since our little boutique consulting company was established in 2004. Aside from its robust analytical engines that improved on PSSE’s capabilities, PSLF also had a very dedicated and responsive development team that was willing to work with us customize the product to our own unique client-driven applications.

Circuit breaker nameplates sometimes indicate only rating on symmetrical short circuit current. In such cases, the rating only reflects the AC component of the short circuit current. A common misinterpretation occurs when one compares the symmetrical short circuit current against the symmetrical short circuit current rating of the circuit breaker for the purposes of circuit breaker duty evaluation. This article provides pointers to avoid making the mistake.

Why is X/R Ratio Important?

Short circuit analysis is a critical piece of the engineering study for a power system. This analysis determines the maximum available fault current in the system, and hence the maximum level that the electrical equipment should be able to withstand.

When a short circuit occurs, the total short circuit current consists of:

• ·        AC component (varies sinusoidally with time), also known as symmetrical current
• ·        DC component (non periodic and decays exponentially with a time constant L/R;  L/R is proportional to X/R)
• ·        The DC component makes the symmetrical current become asymmetrical.

The X/R ratio affects the dc component, and therefore, also the total current. The higher the X/R ratio of a circuit, the longer the dc component will take to decay (longer time constant).

How to integrate a long-term view to the development of transmission systems? This is the challenge of transmission planning: to take into account future uncertainty, new power technologies and economic and operating realities in order to come up with a plan for transmission development.

In the new and emerging competitive markets, transmission planning needs to demonstrate relevance by providing applicable solutions to anticipated problems. In doing so, planners must provide answers to questions that have not yet been asked.

We will cover the various methodologies that have been tried, and point out the ones that work, and don’t work in the new competitive environment. We will discuss the methodologies for developing the strategic plan, and software-based approach to developing the implementation plan. We address the least-cost methodology, and how this is applicable to modern power systems. Finally, the course will discuss the possible future impacts in increasing penetration of renewable energies into the bulk power system, how to address them and how to plan for them.

Nodal pricing is the emerging method for determining the impact of transmission congestion and losses on the price of electric energy. The method involves an optimization solution of costs subject to transmission constraints. This method bears more resemblance to the power flow than to a bidding program. Nodal pricing is applied, in varying forms, to energy markets, congestion rents, firm transmission rights, and others. For anyone participating in such markets, understanding the fundamentals of nodal pricing is a must.

This course provides an introductory coverage of the basics of modeling and calculating nodal pricing, starting from power flow models and cost curves. Case studies and exercises help bring home the concepts while providing real-life examples. The investment of your time and focus will surely be rewarded with a jump start on this important concept of nodal pricing.

Utilities, architect-engineers, developers and industrials are often faced with considering an underground cable option either as a portion of an otherwise overhead line, to connect nearby substations, as entry to an already congested substation, or in urban setting where underground transmission or distribution is the only alternative. The student attending this course will gain an overall understanding of the major cable system types including extruded, self-contained fluid-filled and pipe-type, as well as an understanding about elements of design, manufacturing, installation and operation of underground transmission and distribution cables. More often, transmission cable systems are engineered on a case-by-case basis, so much of the 3-day course focuses on transmission with relevant references to distribution voltage cables. The instructor will discuss topics that are relevant for both voltage classes.

In the accelerated environments of today’s electric energy markets, fast analyses of power flows are a must. Emerging real-time and day-ahead markets require that analysis of infrastructure capacity be performed in a compressed timeframe. In this context, approximate but fast and consistent power flow solutions are preferred over accurate but unwieldy ones. Hence, the increasing popularity of linear approximations to the power flow. The reason for widespread use may have to do with the fact that linear methods are much easier to apply, are not subject to convergence issues, and require less data.

In this introductory course, learn about the technology of linear power flows and apply them to real-world practical problems. Use this technology in applications such as anticipatory analysis of pricing and demand signals, transactional analysis of power interchange and delivery, transmission loading relief and feasibility analysis. In addition, learn about the limitations to these methods and the pitfalls to watch out for when applying these methods. Come away with a working knowledge of the technology of linear power flows.