How Multi-Function Numerical Protection Relays Use Symmetrical Components

Steve Turner, Arizona Public Service CompanyColumns, Relay Column, Summer 2019 Columns

Multi-function protection relays calculate and use symmetrical components to enhance their performance during system faults. This can be illustrated in two specific examples: (1) zero-sequence current elimination for transformer differential protection and (2) negative-sequence current detection to inhibit out-of-step blocking. Zigzag Transformer Inside Transformer Differential Zone A shunt-connected zigzag transformer provides a zero-sequence current sink for ungrounded systems such as …

Dynamic Testing of Numerical Protection Relays

Steve Turner, Arizona Public Service CompanyColumns, Relay Column, Spring 2019 Columns

A numerical protection relay provides multiple functions and typically uses algorithms that do not work on the same principles as older electromechanical relays. Numerical relays are often still tested using old techniques developed long ago for electromechanical relays. One such common technique is referred to as a “static test.” Fault voltage and/or fault current are injected to see whether the …