Application of islanding protection for industrial & commercial generators a 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. A tendency is to look at the consequences of just their own ICG trying to serve a much larger utility load without considering that there may be other ICG connected to the same circuit. 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. Different scenarios of islanding operation are presented, such as: is it necessary to enforce separation of loads that are outside the premises of the owner of the energy source, while retaining service to loads within the owner's premises, or is it acceptable to simply shut down the ICG until the grid can be restored? A basic step in addressing islanding protection is to have a clear expectation of what is supposed to happen when an island is created. This paper elaborates on the proper required protection and how 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. Examples of these consequences are given. This paper will provide a clearer understanding to ICG owners of why they are required to have specified protective equipment in place