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.

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.

(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.

A wave of new solar photovoltaic (“PV”) installations for power generation is hitting many distribution circuits around the country. These installations are typically in the range of 10-2000 kW and comprise of a set of solar PV arrays or trays and inverter modules. The inverters are needed to change the direct-current produced by the arrays to the alternating current standard used by the distribution circuits. The smaller installations connect single-phase, while the larger sizes are three-phase. Interconnection voltage at the point of common coupling between the PV installation and the distribution circuit varies from 120 volt up to 34.5 kilovolt (“kV”).

The concept of integrating these new PV installations with existing distribution circuits is similar to that of interconnecting larger generators in the transmission grid; i.e., the new installation should “do no harm” to the existing system. There are three aspects to this concept as follows. (1) If the existing circuit meets specified standards or criteria of performance, the circuit should still meet the same standard or criteria when the new PV is installed. (2) If the new PV introduces a violation of standard or criteria, mitigation measures need to be included as part of the the new PV’s installation to resolve the violation. (3) If the existing circuit already violates a standard or criteria, the new PV either should not make the violation worse, or limit its impact such that the violation is not worse or even reduced or eliminated.

Pterra conducts training in power technology subjects, not as a primary line, but in response to a perceived need. Occasionally, work in analytical consulting leads to knowledge and skills that clients and associates desire to acquire. And we are more than happy to oblige, if only to break the stream of days spent talking to computers (instead of people). Plus there is something strangely attractive in speaking to minds that are just exploring this lifetime field, electric power. We hope that most will stay on and help the industry. And we hope that some new insight will consolidate our own understanding of how electrons move. This is not to say that these courses are aimed for Gen X’ers alone. But a noticeable percentage who attend do come from that demo.

If only for this one new feature, the trip to attend the meeting (held April 28-29 in sunny Orlando, Florida) was worth it. The new feature is …

PSLF now allows “continuous” tap solutions for phase angle regulators, or PARs. Why does this matter? It matters a lot to those who work in the U.S. Eastern Interconnection (EIC) where most utilities use the competing software package, PSS/E.

Whereas, power plants using renewable energy sources were not too long ago considered exotic, today they are the new face of energy — the wind mill replacing the smokestack as the symbol of electric power generation. Spurred by governmental incentives, renewable energy sources are rapidly changing the nature and composition of power systems. They are still a fraction of the overall energy portfolio, but the renewables’ level of penetration of energy markets is growing. In most US RTOs and power pools, the queue for interconnection projects is dominated by renewables, primarily wind farms.

Conventional wisdom says that the more motors connected to a feeder, the faster voltage will collapse when there is a reactive deficiency. This is true to the extent that voltages do drop faster, but the voltage may not fall all the way — so a voltage collapse does notoccur. A different and more common state is reached when the feeder is in a quasi-equilibrium state at a low per unit voltage. This is the Voltage Ledge.