Disturbance Analysis for Power Systems

Chapter 5

Case Studies Related to Transformer System Disturbances

The use of digital fault recorders with a limited number of analog channels at a large substation has affected the option of monitoring transformer high-side, low-side, and tertiary winding currents. Therefore, the use of transformer multifunction numerical relays has enhanced the monitoring and analysis of transformer disturbances. This is accomplished by providing oscillography records for the transformer current input at all voltage levels.

In this chapter we provide analyses and lessons learned from many disturbance case studies. Energization of a transformer with a high-voltage lead fault will document the generation of enough harmonics to prevent operation of the differential element and recommend reliance on different protection operating principles to clear these types of faults. Violation of the simple duality rule, where two or more elements, with a preference for diverse operating concepts, are used for transformer protection is explained. The failures of an autotransformer and a station service auxiliary transformer are analyzed. Recorded currents on the grounded-wye side are utilized to locate and classify faults on the delta winding of a two-winding transformer.

Disturbance analysis of many phase-to-phase and evolving three-phase faults around the leads of station service transformers and falling within transformer protection zones is also covered. The basics of successful implementation of electromechanical ...