New approach to improve sensitivity of differential and restricted earth fault protections for industrial transformers

Teymoor Ghanbari; Haidar Samet; Javad Ghafourifard

New approach to improve sensitivity of differential and restricted earth fault protections for industrial transformers

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Author(s): Teymoor Ghanbari ¹ ; Haidar Samet ² ; Javad Ghafourifard ²
- Affiliations: 1: School of Advanced Technologies, Shiraz University, Shiraz, Iran ;
  2: Department of Power and Control Engineering, School of Electrical and Computer Engineering, Shiraz University, Shiraz, Iran
Source: Volume 10, Issue 6, 21 April 2016, p. 1486 – 1494
DOI: 10.1049/iet-gtd.2015.1343 , Print ISSN 1751-8687, Online ISSN 1751-8695

Received 16/07/2015, Accepted 26/12/2015, Published 21/04/2016

Differential relays are the main protection for power transformers including transmission and industrial transformers. Protection against internal fault is generally relegated to these relays. The most probable internal fault of the industrial transformer is phase to ground type. To limit the fault current in this condition, a limiter resistor is utilised in the transformer. However, it has considerable impact on sensitivity of the differential and restricted earth fault (REF) protections. In this study, an effective approach is proposed to improve the differential and REF protections sensitivity of the industrial transformers. The proposed technique not only realises the fault current limitation function, but preserves sensitivity of the protections. In this method, a developed fault current limiter is utilised in the transformer neutral instead of the neutral grounding resistor. The performance of the proposed technique is evaluated by some simulations and experiments. The results confirm the high capability of the proposed technique in different conditions.

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New approach to improve sensitivity of differential and restricted earth fault protections for industrial transformers

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