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.

Distributed generators (DGs) are small generating units that are connected to the distribution network at voltages below 69 kV. DG units usually have capacities of 10MW or less, and are based on different energy sources, such as wind, solar and diesel. The distribution network is generally a radial system and designed for one direction of load flow, i.e. from the electric grid to the load. The unidirectional flow assumption is no longer valid when DG is interconnected at the customer or load side since the flow of power can now go in either direction: from the load side to the grid or from the grid to the load side. This fundamental change affects how an impact study, generally required to identify and mitigate any changes to reliability of the distribution system, for DG interconnection is conducted. Reference 1 summarizes several typical tasks required in an interconnection impact study.

by K. Dartawan, R. Austria

What is Distributed Generation (DG)? Unlike big generation stations connected directly to the utility’s transmission grid, DG is typically smaller, about 10 MW or less connected to the distribution network or customer side. The DG could be fueled by renewable sources such as photovoltaic (solar), wind, bio mass or could be non-renewable energy such as diesel or gas.

by E. Cano, K. Dartawan, R. Austria
One potential impact of interconnecting distributed generation (DG) is the potential sympathetic tripping of overcurrent (OC) protection devices, where a healthy feeder trips unnecessarily for a fault on another feeder. The sympathetic tripping comes from DG with high short-circuit current contribution (typically rotating machines such as Diesel or Gas Turbine units) and can be observed in radial feeders that are fed from a common source.

Also, this issue applies to DG on a lateral-backfeed from the DG to the adjacent lateral circuit.