By R. Austria, R. Tapia, K. Dartawan, M. Gutierrez, M. Infantado

For a company to have made it through its 14^th year is not much to crow about. After all, businesses do this all the time. For a boutique consulting company such as Pterra, we would not crow about this either, not about the fact that the company celebrated its 14^th year of incorporation on June 29^th, 2018.  But we would be remiss if we said we had nothing to be thankful about, for the weight of these past 14 years is carried in terms of good memories, tough challenges and the enlightening fellowship of colleagues, friends and families all of which were intrinsic to the Pterra mosaic.

We did write a review of our first 7 years (see An Anniversary) and promised to do another in 7 more years. And we are already here, almost in the blink of an eye.

By Ketut Dartawan

(This topic was presented at the PSCAD Users group Meeting held in Atlanta, GA on Sept. 20-21, 2018. For the full presentation, please see this link.)

Many interconnection challenges exist when connecting photovoltaic (PV) resources to the electrical distribution grid. Various challenges on the distribution feeders are covered in some technical papers; however, one of the urgent topics – as recently mentioned by utilities and recognized by inverter manufacturers as well as the developers – is the potential for ground fault overvoltage (GFO) on sub-transmission systems feeding distribution feeders via a delta-wye transformer (see Figure 1).

by  Ketut Dartawan,  Amin M. Najafabadi

Pterra is presenting a paper on the above subject at the IEEE General Meeting 2017- Chicago 16~20 July.  Abstract of the paper follows:

IEEE updated its recommended practice and requirement for harmonic control in electric power system after more than two decades. The most updated version of the standard (IEEE Std. 519-2014) revised the 1992 version and its static harmonic voltage and current limits. Unlike the 1992 and the older versions of the standard, the 2014 version introduces a newer approach which considers the stochastic nature of harmonic distortions.  Furthermore, it recommends limits based on the number of times distortions may occur. For example, for the harmonic current distortion, it recommends three limits: daily 99th percentile, weekly 99th percentile, and weekly 95th percentile values. Applying the IEEE Std. 519-2014 for planning studies and for harmonic assessment of proposed projects can be very challenging because presently there is no known commercial tool which fully considers the stochastic simulations and limits required in the standard. This paper demonstrates the approach used by the authors in applying IEEE Std. 519-2014 to a harmonic study recently performed for a 180 MW solar farm.

Index Terms- harmonic analysis, harmonic filters, solar power generation, statistical analysis, time series analysis

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.