A Novel Solution to Restricted Earth Fault Low Impedance Relay Maloperation

In this paper, various methods of providing restricted earth fault protection are discussed. The proper operation of high and low impedance Restricted Earth Fault (REF) protection for various applications has been discussed. The maloperation of a relay due to improper placement of CTs has been identified and a simple/unique solution has been proposed in this work with a case study. Moreover, it is found that the proper placement of CT in high impedance method will provide the same result with reduced CT. This methodology has been successfully implemented in Al Takreer refinery for a 2000 KVA transformer. The outcome of the paper may be included in IEEEC37.91 standard to give the proper guidance for protection engineers to sort out the issues related to mal functioning of REF relays.

Authors:

• K. N. Dinesh Babu
• R. Ramaprabha
• V. Rajini
• V. Nagarajan

Keywords:

• Relay maloperation
• transformer
• low impedance REF
• MatLab
• 64R
• IEEE C37.91.

References:

[1] V K Metha & Rohit Metha, Principles of power system, ISBN:81-219-
2496-0.
[2] Sunil S Rao, Switchgear and protection, Khanna publishers, fourth
reprint, 1996.
[3] T60 transformer protection system, UR series instruction annual, version
7.2x, Manual P/N:1601-0090-AA1 (GEK-119568)
[4] High impedance restricted earth fault protection, technical guidance
notes, SIEMENS.
[5] IEEE guide for protective relay applications to power transformers,
C37.91-2000