Application of islanding protection for industrial and commercial generators-an IEEE industrial application society working group report

Many owners of distributed resources such as synchronous industrial plant or commercial facility generators (ICG) are concerned about the requirements for protective relaying when connecting to a local utility. The connection may only be for a short transfer time of a few seconds during paralleling for periodic testing. The power rating of an ICG is not important when considering protective relays required, because several small engine generators of 100 kW or a single larger ICG of 10.0 MW could form an island. Thus, all ICG connected to an electric power system usually are required to have the same protection in place at their point of common coupling. This paper elaborates on the protection and its operation will prevent undesired consequences to the ICG owner, the utility and to the general public. The paper also discusses actions that take place when the utility supply is disrupted creating an islanding condition, and states reasons why protection required by regulatory agencies, local utilities and documents such as IEEE Standard 1547 "IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems" are required of an individual ICG. Consequences of not having the protection in place can permit damage to the generator and/or its prime mover, plus be a hazard to public safety.