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).

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.

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.

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.

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.

In various Blogs on this site, we have talked about unique technical issues associated with integrating wind farms into existing grids. This Blog now addresses the matter of transient overvoltages, or TOV, specifically with respect to potential risks to customers and any required mitigation associated with wind farms installations.