Distance elements: Linking theory with testing

Understanding and testing distance elements require linking the theory related to their design to the fault voltages and currents used during tests. This paper discusses the theory, deriving the characteristics of phase and ground distance elements with a focus on three in particular. The derivation will introduce certain concepts, including the impedance plane, source impedance, forward fault impedance, reverse fault impedance, fault resistance, and load flow behavior. The discussion is based on the use of symmetrical components to understand the design, behavior, and characteristics of distance elements. This paper also reviews some testing procedural errors. A confident understanding of the theory allows for an easier understanding of the testing results obtained.