Forward to the basics: Selected topics in distribution protection

Modern relays provide protection elements that were historically not used due to cost or panel space restrictions. These new elements can provide improved protection for the power system. However, protection engineers may be unfamiliar with the behavior of these elements and may make settings choices that lead to unintended consequences. At the same time, engineers must continue to properly employ good settings practices, long established for more traditional elements. Through analysis of event reports recorded by relays, this paper will present several examples of settings that led to unintended operation of distribution protection, including transformer delta-winding residual overcurrent protection, transformer high-voltage phase overcurrent protection, and others. The nature of the unintended operations will be explored, and methods for calculating more secure settings will be discussed.