Electric Power Engineers (EPE) Completes Evaluation of 9.6 MW Distributed Gas Generation Project with Microgrid Interconnection
Austin, Texas, December xx, 2019 – EPE announced today that it has completed the evaluation of a distributed gas-fired generating project with microgrid interconnection. The project has been designed to operate within a campus environment, and to be connected to the local municipal utility’s 12.47 kV feeder.
The review was requested by the local utility to ensure that the proposed distributed system would safely and reliably interact through the local feed line with the municipal power grid. In the course of its thorough testing protocols, EPE completed load flow, short circuit, protection coordination, and arc flash studies.
The specific objectives of testing included:
- Assess the impact of the project on the distribution feeder, with attention given to voltage rise/drop, thermal loading, voltage flicker, and back-feed to the transmission system.
- Identify protection equipment exceeding short circuit ratings.
- Analyze coordination of protection equipment and determine appropriate settings for feeder reclosers.
- Determine the arc flash boundary and arc flash incident energy, and recommend personal protective equipment for minimizing the potential for injury in the event of an arc flash incident.
Impact on distribution feeder - EPE’s load flow analysis in WindMil® evaluated potential impacts of the proposed project on the distribution feeder, including maximum and minimum load levels, and four modes of operation: fully online, partially online, offline, and not connected (i.e., operating as an island). No thermal loading violations were identified, although voltage violations exceeding +5% were detected for one scenario. EPE also identified no adverse effects on voltage levels or thermal loading resulting from transmission contingencies around the substation when subjected to full export from the generating units.
Short circuit study – EPE’s review did not find any protection devices for which fault current ratings were exceeded. However, it did make some recommendations concerning reclosers.
Protection coordination – EPE analyzed the trip currents and TCC curves for the two reclosers on the local feeder and found that during full export of 9.6 MW, a steady state current of -420 A would be experienced, implying a trip as current would exceed recommended levels. EPE made some commensurate technical recommendations with respect to programming the affected recloser and appropriate TCC curves. EPE also made recommendations concerning generator protection settings and transfer trip, focusing on the potential for feeder or transmission breaker reclosing when the DER‐fed island and the utility source voltages are out of phase, and recommended a transfer trip to protect against islanding whenever the feeder is disconnected with the substation.
Arc flash hazard analysis – EPE’s review indicated that the Point of Interconnection presents the highest incident energy, and recommended the adoption of specific protective clothing to minimize the potential for injury.
In the ERCOT service territory alone, the number of registered distributed generating assets is estimated at 750-850 MW, including a rapidly growing number of gas-fired units. As more of these distributed assets get added to utility grids across the U.S., it is critically important that they are able to perform reliably and safely under a variety of operating circumstances. EPE’s team can help evaluate proposed projects of this nature and ensure that these assets perform as expected.
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Electric Power Engineers, Inc. (EPE) is a leading power engineering consulting firm. EPE offers unparalleled expertise in power system planning, design, and grid integration in the United States and international markets. Our experience and services cover the entire spectrum of GENERATION, TRANSMISSION, and DISTRIBUTION and are provided to developers, generation owners, transmission service providers, municipalities, electric cooperatives, and various government entities.
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