12.5 MVA generator islanding protection

This paper presents the experience in loss of mains protections for distributed generation, during the start up of a synchronous generator of 12.5 MVA. Settings of ROCOFF and Vector Jump protective relaying are commented, as well as the good results obtained during test with utility company realized in a real islanding situation. ATP simulations were executed in several network configurations. Under voltage blocking action was incorporated showing a good behavior during generator operation. In spite of these successful considerations, a lot of undesired disconnections were consequence of loss of mains protection. Network frequency changes were considered the principal cause of relay miss operation. It is considered extremely important the good measurements of frequency time variations previous at generation industrial operation. The way that these measures can be implemented with a power meter is shown. A frequency filter is considered as the solution to network frequencies variations.