Optimal Placement of Automatic Switching Equipment in Radial Distribution Networks Based on Protective Coordination

  • Masoud AmohadiEmail author
  • Mahmud Fotuhi-Firuzabad
Original Article


Automatic switching equipment and protection devices (AS/PDs) play a fundamental role in radial power distribution networks. In this paper, a new hybrid method is presented to determine the optimal number, types, and locations of AS/PDs based on protective coordination. When a short circuit fault occurs in a medium voltage distribution network (MV feeder), AS/PDs such as relays, fuses, auto-reclosers and sectionalizers can be employed to disconnect the faulty part from the healthy area. The use of automatic switches at proper locations can significantly decrease system interruptions. The costs of investment, maintenance, and unsupplied energy are considered in the cost function. This function must be minimized in order to obtain the optimal automatic switches, using particle swarm optimization. Furthermore, ant colony optimization is utilized to specify the main branch of MV feeder. The protection equipment determined in this branch is coordinated to protect the feeder against probable faults. If coordination of PDs is not achieved completely, the sizes and locations of AS/PDs are recalculated. The proposed technique is implemented on a feeder of Isfahan power distribution network, as a sample feeder. The obtained results indicate that the proposed technique is acceptable and efficient.


Reliability parameters Cost/worth analysis PSO algorithm ACO technique Protective coordination Automatic switches placement 


Indices and Sets

i, n

Index and set of feeder’s buses

j, m

Index and set of feeder’s loads

Parameters and Constants


Number of feeder buses


Load reactive power (KVAR)


Load active power (kW)


Length of section (km)

R, X

Line impedance (Ω)


Power losses (kW)


Section voltage (V)


Section current (A)


Short circuit/earth fault current (KA)


Current setting (A)


Time setting (S)


Annual interest rate


Annual inflation rate

X, Y

Load location


Failure rate (f/year)


Average annual interruption time (h/year)

Functions and Variables


Automatic switches/protection devices


System average interruption duration index


System average interruption frequency index


Particle swarm optimization


Ant colony optimization


Energy not supplied


Objective function


Medium voltage


Cost of investment


Cost of energy not supplied


Cost of maintenance


Value of lost load


Over current/earth fault


A breaker controlled with an OC/EF relay



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Copyright information

© The Korean Institute of Electrical Engineers 2019

Authors and Affiliations

  1. 1.Department of Electrical EngineeringIslamic Azad University, Science and Research BranchTehranIran
  2. 2.Department of Electrical EngineeringSharif University of TechnologyTehranIran

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