Applying IEEE Std. 519-2014 for Harmonic Distortion Analysis of a 180 MW Solar PV Installation

April 19, 2017 : Blog, Industry News, Photovoltaic Systems and Distributed Generation, Power Quality, Tech Blog, Technical Papers

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

Authors- Ketut Dartawan, Amin M. Najafabadi

Siting of Power Plants: A Thermal Capacity Assessment for Grid Interconnection

July 13, 2016 : Blog, Power Flow Analysis, Power Flow Analysis, System Planning, Tech Blog, Technical Papers



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.
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The New PSLF

March 18, 2015 : Blog, General, Industry News

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. So we are more than glad to support the next development step for PSLF, as evidenced by our participation in this promotional video for the new PSLF. We will note that neither Pterra nor Ric Austria received remuneration in exchange for our participation.

Role of X/R Ratio in Circuit Breaker Short Circuit Duty Evaluation

January 30, 2015 : Blog, Distribution, Photovoltaic Systems and Distributed Generation, Tech Blog

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). more »

Capacitor Bank Sizing for a Large Wind Farm Project

January 23, 2015 : Blog, New, Power Flow Analysis, Tech Blog, Technical Papers, Wind Power Integration

Pterra’s Amin Najafabadi, Senior Consultant, is presenting on the title subject. This is at the Electric Power Conference and Exhibition to be held in Rosemont, IL, April 23-25, 2015. Following is the abstract of the presentation.

Utilities generally require large wind power plants to meet power factor capability, similar to those of traditional generating facilities such as gas, steam, or coal power plants.  Reactive power compensation equipment such as capacitors, reactors, static VAR compensators, static synchronous compensators, and the like, are usually needed so that a large wind farm project can meet the ±0.95 power factor requirement at the point of interconnection. Switched capacitor banks serve as one of the more effective and economic solutions.

When sizing capacitor banks for a 200 MW wind farm consisting of Type III wind turbine generators, several challenges are encountered due to limitation of power flow programs used in industrial power system application. User’s customized functions and iterations may not be possible to be added to the programs. As alternative tools, Matlab and OpenDSS power flow engines are used in order to meet the requirement and to properly utilize reactive capability from each wind farm unit as well as to update main transformer impedance according to manufacturer specification. The results of the study showed capacitor banks needed for the project are about 30 percent less than the results from traditional power flow program. Simple switching schemes are tested and the voltage change due to capacitor switching is insignificant.

The full text of the presentation will be available at the conference or upon request via

2014 PSCAD User Group Meeting

August 20, 2014 : Blog, General

This year the PSCAD User Group Meeting will be held in NYC!  Pterra will be presenting on a study application of the PSCAD software, so hope to see you there.  Details of the Meeting:

Where: Executive Conference Center, 8th Floor, 1601 Broadway, New York, NY 10019

When: September 25-26, 2014

More information can be found at


Intro to Python Programming

March 15, 2014 : Blog, Standard Courses, Training Courses

Pterra’s next offering in power system training is coming March 25-27, 2014 on the topic “Introduction to Python Programming.”  We are holding the course in sunny (hopefully) and warm (relative to the rest of the country) Tampa, FL and our instructors, who’ve been preparing for most of the winter, are raring to get started.

Python is an open-source, platform-portable programming language that is used as a command and scripting language by some of the more popular software used for electric power system analysis.  Hence, the benefit of taking this course is in learning the basics of the language itself, and how to apply it to utilize analytical software more effectively and efficiently.

In this two-and-a-half day course, we will cover:

  • Python Variable and Data Structures
  • Tuples and Lists
  • Python rules and programming styles
  • Iteration and Flow Control
  • Python String and Formats
  • Modules, Methods and Classes
  • Python Input and Output\
  • Python interface – using user specific programs
  • Accessing data
  • Data Retrieval and Changing
  • Recording GUI actions and modification with Python
  • Customized Text Input / Output
  • Python – Communication with MS Excel for reporting
  • Adding activities using Python

As with all other Pterra courses, the focus is on practical applications to real world power system problems, hence, up to half of the course time is allocated to guided hands-on exercises in direct interaction with the course instructors.

Pterra is proud to offer this new course to power system engineers.  Limited seats are still available.  For information, contact

Transmission Planning Course

November 27, 2013 : New, Training Courses

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.

Understanding Location-Based Energy Pricing

November 27, 2013 : New, Training Courses

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.

Aspects of Underground Power Cable Systems Course

November 27, 2013 : New, Training Courses

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.


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