Investigating Phase Over-Current (OC) Protection in Medium-Voltage networks


  •   Aniagboso John Onah


Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection. There is always a need to protect expensive power equipment. Protective relaying is a very important part of any electric power system that comes into play during trouble, fault or abnormal condition. The purpose is to isolate unhealthy part of electrical power system while the rest continue their normal operation. The entire electric power system from source to load centers is exposed and subject to natural hazards. The effects of these hazards are capable of interrupting normal operations of the system. Since these hazards cannot be prevented, precautions are taken to minimize or eliminate their effect on the system. The relay is a basic component of any protection scheme. The information (or signals) received from the power system actuates the relay, when necessary, to perform one or more switching actions. The signals are proportional to the magnitudes and phase angles of power system voltages and currents. When the relay receives these signals, it decides to close (or open) one or more sets of normally open (or closed) contacts, and consequently, the trip coil of a circuit breaker will be energized to open the power circuit. This paper investigates over-current relay protection scheme applied to medium-voltage electrical network. Methods of current and time grading have been applied in the coordination of the overcurrent relays in a radial network. Different time/current characteristics of relays such as the normal inverse (NI), very inverse (VI), and extreme inverse (EI) have been examined in order to obtain optimum discrimination.

Keywords: Circuit Breaker, Fault, Overcurrent, Protection, Relay


J.A. Kay, and L. Kumpulainen, “Maximizing Protection by minimizing arcing times in medium-voltage systems,” IEEE Trans. Ind. Appl., vol. 49, No. 4, pp.1920-1927, July-August, 2013.

M. Mitolo, and M. Tartaglia, “An Analytical Evaluation of the factor k2 for protective conductors,” IEEE Trans. Ind. Appl., vol. 48, No. 1, pp.211-217, January-February, 2012.

IEEE, “IEEE guide for protecting power transformers,” IEEE Standard C37.91, 2008.

IEEE, “IEEE guide for automatic reclosing of line circuit breakers for ac distribution and transmission lines,” IEEE Standard C37.104, 2002.

M.J. Slabbert, S.J. van Zyl, R. Naidoo, and R.C. Bansal, “Evaluating Phase Over-Current Protection Philosophies for Medium-Voltage Feeders Applying Let-through Energy and Voltage Dip Minimization,” Electric Power Components and Systems, Vol. 44 (2016), No. 2, pp. 206-218.

C.A. Gross, Power System Analysis, USA: John Wiley& Sons, 1979, pp. 351.

C. Christopoulos, A. Wright, “Electrical Power System Protection”, Kluwer Academic Publishers, the Netherlands, 1999, pp 107-134

I. J. Nagrath, D. P. Kothari, Power System Engineering, New Delhi: Tata McGraw Hill, 2002, pp 659-660.

G. Kangle, C. Myeonsong, L. SeungJea, and H.L. Seong, “Coordination Method for Protective devices of closed-loop distribution system,” Proc. Of the 11th Environmental and Electrical Engineering International Conference (EEEIC), pp. 47-52, Venice, 18-25 May 2012.

IEEE, “IEEE guide for protective relay applications to distribution lines,” IEEE Standard C37.230, 2007.automatic reclosing of line circuit breakers for ac distribution and transmission lines,” IEEE Standard C37.104, 2002.

D.P. Roth, “Maximizing Protection Coordination with Self-healing Technology,” IEEE Rural Electric Power Conference (REPC), pp. B4-1-B4-12, Milwaukee, W1, 15-17 April 2012

S. O. Arreola, A. CondeEnriquez, and L.A.Trujillo Guajardo, “Overcurrent Relay with unconventional curves and its application in industrial power systems,” Electric Power System Res. Vol. 110, pp. 113-121, May 2014

A.R. van C. Warrington, Protective Relays: Their Theory and Practice, Chapman and Hall, 1971, pp. 141-190.

T. Keil, and J. Jager, “Advanced Coordination Method for Overcurrent Relays using nonstandard tripping characteristics,” IEEE Trans. Power Del., Vol. 23, No. 1, pp. 52-57, January 2008.

A.F. Naiem, A.Y. Abdelaziz, Y. Hegazy, and M.A. Elsharkawy, “Recloser-fuse coordination assessment by classification technique for distribution systems with distributed generation,” Electric Power Component and Systems, Vol. 39, No. 11, pp. 1077-1096, 2011.

T. Davies, Protection of Industrial Power Systems, Oxford: Newnes, 2001, pp 81-94.

M. R. Russell, and R. Poteet, ”Transmission and Distribution World,” October, 1998.

D.J. Lee, and C.H. Kim, “An analysis of let-through I2R variations of a current limiting circuit breaker by non-simultaneous closing in short-circuit conditions,” Electric Power Component and Systems, Vol. 36, No. 10, pp. 1067-1079, 2008.

T. Papallo, and M.E. Valdes, “Traditional time-current curves are not enough, adding I2t considerations,” IEEE Trans. Ind. Appl. Vol. 49, No. 1, pp. 264-274, January-February, 2013.

E.S. Thomas, “Bonding requirements for conductive poles,” IEEE Rural Electric Power Conference (REPC), pp. A4-1-A4-6, Milwaukee, W1, 15-17 April 2012.

P. Thakur, A.K. Singh, and R.C. Bansal, “A Novel to distinguish single-phase dips through potential gradient method,” Electric Power Component and Systems, Vol. 40, No. 3, pp. 336-347, 2012.

S.R. Naidu, G.V. de Andrade, and E.G. da Costa, “Voltage Sag Performance of a Distribution System and its Improvement,” IEEE Trans. Ind. Appl. Vol. 48, No. 1, pp. 218-224, January-February, 2012.

R. Barr, and V. Gosbell, “Voltage Sags – customer needs versus what distributors can deliver,” Annual Conference of Electric Energy Association of Australia, Canberra, Australia, 9-10 August, 2002.

NRS, “Electricity Supply-quality of supply-voltage characteristics, compatibility levels, limits and assessment methods,” NRS 048-2, 2003.

D. Chapman, “Power quality application guide-voltage dips, “November 2001, available at: quality-and-utilization-guide.

T.W. Cease, “Protective relaying and power quality,” IEEE PSRC Working Group, available at:


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How to Cite
Onah, A. 2019. Investigating Phase Over-Current (OC) Protection in Medium-Voltage networks. European Journal of Engineering and Technology Research. 4, 6 (Jun. 2019), 41-49. DOI: