Power Transformer Characteristics and Their Effect on Protective Relays

Fahrudin Mekic, ABB  - Allentown, PA
Ramsis Girgis, ABB - St. Louis, MO
Zoran Gajic, ABB - Vasteras, Sweden
Ed teNyenhuis, ABB - Brampton, Canada

There are a variety of protective relays using different measuring techniques to provide reliable and secure transformer protection. This includes electro-mechanical, solid state and numerical relays. Within each group, various algorithms exist. Advancements made to transformer technology and design over the past 3 decades, have changed the characteristics of the transformer inrush current, and have often introduced incorrect operations in the existing harmonic restraint relays during energization. The paper discusses:

  • Comparison between old and newly developed more accurate calculations of peak values, magnitude of the second harmonic, and other parameters of Inrush current
  • Design and system parameters which influence the magnitude and wave-shape of inrush current, e.g. winding design and connections, core material, core joint geometry, short-circuit capacity of network, etc.
  • Impact of transformer design & performance parameters and new developments in the Transformer technology on magnitudes and nature of inrush current
  • Current transformer influence on the speed, selectivity, and dependability of transformer protection

The paper addresses these topics, as well as provides solutions for selecting and setting transformer protection.

PDF Version

BeijingSifang June 2016