Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 30075
Analysis of the Root Causes of Transformer Bushing Failures

Authors: E. A. Feilat, I. A. Metwally, S. Al-Matri, A. S. Al-Abri


This paper presents the results of a comprehensive investigation of five blackouts that occurred on 28 August to 8 September 2011 due to bushing failures of the 132/33 kV, 125 MVA transformers at JBB Ali Grid station. The investigation aims to explore the root causes of the bushing failures and come up with recommendations that help in rectifying the problem and avoiding the reoccurrence of similar type of incidents. The incident reports about the failed bushings and the SCADA reports at this grid station were examined and analyzed. Moreover, comprehensive power quality field measurements at ten 33/11 kV substations (S/Ss) in JBB Ali area were conducted, and frequency scans were performed to verify any harmonic resonance frequencies due to power factor correction capacitors. Furthermore, the daily operations of the on-load tap changers (OLTCs) of both the 125 MVA and 20 MVA transformers at JBB Ali Grid station have been analyzed. The investigation showed that the five bushing failures were due to a local problem, i.e. internal degradation of the bushing insulation. This has been confirmed by analyzing the time interval between successive OLTC operations of the faulty grid transformers. It was also found that monitoring the number of OLTC operations can help in predicting bushing failure.

Keywords: Modeling and simulation, power system, transformer, bushing, OLTC, power quality, partial discharge.

Digital Object Identifier (DOI):

Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 9885


[1] CIGRE-WG 12-05: An international survey on failures in large power transformers in service, Electra No. 88 1983, S. 21-48.
[2] P. Singh, "C2 Power factor and capacitance of ABB type O plus C, AB, and Type T condenser bushings," Doble Client Conference Paper, 2001.
[3] I. A. Metwally, "Failures, monitoring, and new trends of power transformers," IEEE Potentials, May/June 2011, pp. 36-43.
[4] T. E. Grebe, "Application of distribution system capacitor banks and their impact on power quality," IEEE Trans. Industry Applications, Vol. 32, No. 3, May/June 1996, pp. 714-719.
[5] R. C. Dugan, M. F. McGranaghan, S. Santoso, and H. W. Beaty, Electrical Power Systems Quality, Second Edition, McGraw-Hill, 2004.
[6] IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems, IEEE Std. 519-1992.
[7] ETAP-7.5 power system software. Operation Technology, Inc., Irvine, CA,
[8] G. Brunello, B. Kasztenny, and C. Wester, "Shunt capacitor bank fundamentals and protection," 2003 Conference for Protective Relay Engineers, Texas A&M University, April 8-10, 2003, College Station (TX), USA.
[9] ABB Components, "On-load tap-changers for industrial applications," Available: