Evaluating Phase Over-current Protection Philosophies for Medium-voltage Feeders Applying Let-through Energy and Voltage Dip Minimization

Abstract

The effectiveness of phase over-current protection cannot be evaluated by using time-current graphs alone. This article develops a method to evaluate and optimize the phase over-current protection on a radial medium-voltage distribution feeder, which can reduce the risk at the point of fault and improves the overall reliability of the feeder. The method is based on the evaluation of protection operating time, let-through energy, pickup sensitivity, and extent of the voltage dips experienced at the point of common coupling due to network faults under high- and low-source impedance conditions. A Microsoft Excel-based software application (Microsoft, Redmond, WA, USA) is developed that incorporates the four evaluation measures under user-definable network criteria. The application illustrates the results in unique, special forms across the analyzed path and allows the benefits of small changes in protection settings to be quantified. The method and software applications are applied in two case studies on an actual distribution network. The results confirm that it is possible to evaluate the effectiveness of the phase over-current protection philosophy using the aforementioned criteria.

Keywords::

• let-through energy
• medium voltage
• protection
• radial feeder
• reliability
• sensitivity
• voltage dip

Additional information

Notes on contributors

Martin J. Slabbert

Martin Slabbert completed his national diploma (NDip) in electrical engineering, specializing in digital technology, at Technicon Pretoria, South Africa, in 2002. He then completed his B.Eng. in electrical engineering at the University of Pretoria, South Africa, in 2008. He completed his B.Eng. (hons) in 2010 and went on to complete his M.Eng. in 2015 at the same institution. Since 2013, he has been working for the South African power utility, Eskom, as a senior electrical engineer in the system operator. From 2008 to 2013, he worked for Eskom as a protection settings engineer in the distribution division. He is registered with the Engineering Council of South Africa as a professional engineer. His current interests are power system protection with a focus on MV feeder protection.

Stuart J. van Zyl

Stuart van Zyl received his B.Sc. in physics and mathematics in 1996, his B.Sc. in electrical engineering in 1998, and his M.Sc. in electrical engineering in 2004, all from University of Cape Town, South Africa. He has worked as a power system protection engineer for the South African power utility, Eskom, since 1999. He is a chief engineer specializing in distribution protection for the Eskom wires business. He is a senior member of the South African Institute of Electrical Engineers (SAIEE) and a registered professional engineer in South Africa. His research interests are medium- and low-voltage protection and public safety. He is responsible for national contracts for protection schemes, protection technology direction setting, investigations, and technology management.

Raj Naidoo

Raj Naidoo has more than 20 years of teaching, research, and industrial experience. He received his bachelor's degree in electrical engineering from the University of Natal in 1995, his master's degree from University of Witwatersrand in 2000, and his Ph.D. in electrical engineering at the University of Cape Town, South Africa, in 2008. He is currently a faculty member in the Department of Electrical, Electronic, and Computer Engineering at the University of Pretoria, South Africa. He was previously the CEO of Enermatics Energy and has also worked and consulted with several blue chip companies, including the power utility, Eskom. He is a director at Stellenbosch Wind Energy Technology, a spin-off company of Stellenbosch University. He has published several research articles in journals and conferences. He has diversified research interests in the areas of the smart grid, renewable energy, and power systems.

Ramesh C. Bansal

Ramesh C. Bansal has more than 25 years of teaching, research, and industrial experience. Currently, he is the professor and group head (power) in the Department of Electrical, Electronic, and Computer Engineering at the University of Pretoria, South Africa. In previous postings, he was with the University of Queensland, Australia; Birla Institute of Technology and Science, Pilani, India; University of the South Pacific, Fiji; and Civil Construction Wing, All India Radio. He has published over 230 articles in journals and conferences. He is an editor/associate editor of many reputed journals, including IET-Renewable Power Generation, IEEE Access, and Electric Power Components and Systems. He is a fellow of CEngg IET-UK, a fellow of Engineers Australia, a fellow of the Institution of Engineers (India), and senior member of the IEEE. He has diversified research interests in the areas of renewable energy and conventional power systems, which include wind, photovoltaic, hybrid power systems, distributed generation, grid integration of renewable energy, power systems analysis (reactive power/voltage control, stability, faults and protection), smart grid, flexible AC transmission systems, and power quality.