Power engineering effective solution triangle customer-consultant-manufacturer: a case history on meeting energy let-through requirements for a distribution transformer

Maximizing the reliability of a medium-voltage energy-delivery system requires an extensive amount of distribution engineering knowledge. When that system is to have the added flexibility of having its standby generators operate while tied into the utility grid, the depth of the knowledge needed increases significantly. In many cases, it would require more knowledge than many experienced consulting firms might possess. The standby generator project case history discussed in this paper involved a lesser known but very important code compliance issue. That issue became important when less-flammable oil-filled pad-mounted transformers were selected to provide an isolating link between those generators and the utility distribution system serving a commercial facility. The isolating link was intended to protect those generators from damage should they suffer ground faults. This paper is intended to point out two important facts. First, to provide an explanation and background of what is a lesser known, yet critically important, issue-specifically, the requirement that "maximum i²t let-through limits" for less-flammable transformers comply with NEC Listing requirements. Secondly, the paper points out how the broad network of talented engineers within the Industrial and Commercial Power Systems (I&CPS) Department of the IEEE Industry Applications Society was able to help the project\´s design engineer to both understand this issue and to assist in obtaining the equipment needed to successfully complete the project.