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

Power Transformer Characteristics and Their Effect on Protective Relays

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.

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