Presented by Kevin Maynard, Potomac Testing

This talk will discuss the techniques and calculations to set an 87 differential relay. This ANSI function is used in some of the more advanced relays to protect larger generators and are relays that require both a mathematical approach as well as an operational approach. The 87 relay can protect the zone around the generator itself, the zone around a transformer that connects a generator to the system, or even the bus that it connects to. These settings require thought into how the relay is physically set up, what the anticipated current flow through the system is, and what abnormal conditions the relay should show restraint for. A deeper dive with example calculation sheets will be discussed for how to set the 87T, 87G, and 87B relays. This talk will not focus on a single type of relay manufacturer but rather lay out the philosophy that can be applied to any manufacturer or model of relay with the 87 ANSI functions. Other auxiliary generator functions will also be discussed in an overview of a suite of protection for a larger generator.