Transient, Temporary and Ground Fault Overvoltages at Wind Farm Installations

Posted on March 4, 2013 by Administrator

Wind farms by the nature of their design and operating characteristics are susceptible to a variety of overvoltages.  Hence it is always important to conduct studies and tests of the various levels of overvoltages and how the equipment at the wind farm are able to withstand with or without mitigation measures.  In this Blog, we will provide an overview of the issues, the analytical approach and potential mitigation.  Then, we demonstrate how these are applied to a sample wind farm.

Continue reading →

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Flicker Trouble Ahead for Solar PV Inverters?

Posted on February 22, 2013 by Administrator
(Updated March 7, 2013 with additional text shown in red.)

The seemingly innocuous flickering of lamps could be a new technical battleground for the further growth and spread of photovoltaic (“PV”) electric power. On one side of the impending conflict is the flicker standard, a venerable reference that could very well trace its roots back to the advent of the electric age. On the other side are the new darlings of the power industry — environment-friendly, renewable solar power. The one thing about solar power is that in bulk amounts, its units need to be connected to existing electrical systems, and a side effect of this integration is the production of flicker. The more PV devices connected to the same electrical circuit, the more flicker is produced and the closer the level of flicker is to the allowable limit defined by the flicker standard. Continue reading →

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The PTI Song

Posted on February 18, 2013 by Administrator

Click here to play: PTI Lyrics: PTI, we sing to thee, scene of peace and harmony; Watch the mind of each PE, spouting forth technology; We will toil from dawn ‘til night that our brethren may delight; In a life of wealth and luxury, … Continue reading →

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Integrating Solar PV Power with Existing Distribution Circuits; Part 2

Posted on October 23, 2012 by Administrator

(This Blog is a continuation of an ongoing series on integrating inverter-based solar photovoltaic generation with existing electric distribution circuits.  Link to Part 1)

Solar PV (shorthand for photovoltaic) generation is growing in support and implementation in part because of a supportive regulatory environment.  Among the more common types of interconnection terms are NEM and FIT. Continue reading →

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Harmonics Limit Amount of PV on a Distribution Circuit

Posted on June 4, 2012 by Administrator

Harmonics is a very specialized and not widely understood topic in the electric power field which can become a major issue when inverter-based photovoltaic (“PV”) generators, (popularly referred to as solar power), are added to existing distribution circuits.  This Blog provides a quick overview of the phenomena, potential negative impacts, causal conditions, and mitigating measures associated with harmonics.   The bulk of the material presented here is based on an oral presentation at the SOLAR 2012 Conference of the World Renewable Energy Forum (WREF 2012) held last May 13-17, 2012, at the Colorado Convention Center in Denver.  The full paper can be found here. Continue reading →

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The Future of Transient Analysis is Bright

Posted on April 25, 2012 by Administrator

Yes, or at least, it’s brightening.

We make this bold observation after attending the 2012 users’ group meeting for the PSCAD/EMTDC software, held March 27-20 at a little gem of a coastal town named Castelldefels in Spain.  About 60 participants (eyeball count) from universities, manufacturers, utilities, sysops, sales reps and consultants gathered together for techno-talk on the decidedly geeky subject of power system transients and PSCAD applications.

With 22 countries represented, one would have to be positively polyglot to communicate in all the languages spoken by the attendees.  But power system analysis and mathematics make for a universal medium.  Just stay on topic or risk invoking a Tower of Babel event. Continue reading →

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On Engineering Software

Posted on March 29, 2012 by Administrator

As an analytical consulting firm, Pterra regularly uses about half a dozen engineering software, and about the same number on an occasional basis, to be able to conduct its services.  The software are necessary to be able to simulate complex physics and market conditions and/or large scale databases.  In addition, we try to use the same software that our clients use so that part of our deliverable is an updated system model or database.

Craig Muller - PSCAD/EMTDC

Needless to say, the use of engineering software is mission-critical, a situation that is likely repeated in any number of utilities, engineering design firms, system operators, market participants and educational institutions all over the world.  The software needs not only to provide accurate engineering results but also to adopt new technologies such as solar PV, wind turbine, high voltage direct current and frequency converters, market structures and new analytical methods as expeditiously as possible. Continue reading →

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Banking on grounding of solar and wind farms

Posted on March 6, 2012 by Administrator

One more item to add to the list of technical items to consider when interconnecting solar and wind farms is grounding.  The grounding issue often appears when (a) integrating solar power inverters or wind turbines to existing distribution circuits, or (b) designing collector systems for solar and windpower farms.

Most medium to large scale solar inverters and wind turbines are supplied or sold as three-phase, delta or wye-ungrounded systems.  This means their electrical systems have no path to ground of their own.  And therein lies the concern.

When interconnected with grounded or four-wire systems, the inverter or turbine (generalized, for purposes of this article as distributed generation, or “DG“) poses a potential for very high ground fault overvoltages from the phenomenon known as neutral shift. Continue reading →

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Solar Photovoltaic Inverters and Ride-Through Capability

Posted on February 7, 2012 by Administrator

In study after study, we (Pterra) are encountering this seemingly mounting issue of ride-through capability in solar photovoltaic (“PV”) inverters.  For now, the matter is isolated to frequency ride-through in small grids such as those that may be found in the Hawaiian islands.  However, there is potential for this to be critical in even larger systems as the number of inverter-based PV arrays interconnecting to existing distribution and transmission systems increases.

The crux of the present issue relates to the frequency ride-through settings and capability for commercial PV inverters.  The industry standard that addresses frequency settings for solar PV is IEEE standard 1547, Interconnecting Distributed Resources With Electric Power Systems, which specifies that (for 60 Hz systems):

  • For inverters < 30 kW, trip at frequency < 59.3 Hz clearing in 0.16 sec
  • For inverters > 30 kW, trip at frequencies 57-59.8 Hz clearing in 0.16 to 300 sec (adjustable setpoint), or at frequency < 57 Hz clearing in 016 sec

Certain commercial PV inverters are equipped with extended frequency ride-through capability that will not trip until frequency drops below 55 Hz. Continue reading →

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Can wind turbines and solar inverters contribute to frequency control?

Posted on February 6, 2012 by Administrator

Renewable energy resources such as solar and wind, produce power in a manner that generally does not contribute to frequency control of interconnected power systems.  For wind turbines, the reason for this is that the generators used to convert wind to electric energy have small inertias that dissipate rotational energy more readily than conventional steam turbines.  Also, wind turbines are operated such as to generate optimal power from the available wind, and hence do not have much spinning reserve.  For inverter-based solar generation, the solid-state controls have no rotating component at all.  (Solar thermal power is usually produced with synchronous generators and thus contribute to frequency control as most thermal-type power plants are able to do.)

However, both wind turbines and solar inverters have the important characteristic of fast, programmable controls.  The question then comes up: Is it possible for these power sources to participate in frequency control response of interconnections?   This is an intriguing question that merits some further investigation.   Continue reading →

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