The tap changing transformer is one of the important methods of voltage control. It works on the principle of regulating the secondary voltage based on the concept of changing the number of turns on the primary or secondary side of the transformer. An increase in the primary turns result in a corresponding increase in the magnitude of emf per turn, and hence an increase in the secondary output voltage.

This paper establishes the impact of tap changing transformers on the loss minimization of electrical power distribution feeders using ten selected feeders each of Kaduna and Port-Harcourt distribution systems as case studies. The loaded primary radial feeders were divided into load sections with a tap changing transformer at the beginning of the distribution network. The mathematical formulation for the minimization of power loss tap changer problem was done to find the tap setting of the substation transformer that would give minimum distribution loss while satisfying the operating constraints under a certain load pattern. These operating constraints are voltage drop, current capacity and radial operating structure of the system.

The maximum load at the nodes and distances between nodes were obtained from the network layout of the Power Distribution Centre. The voltage drops and power losses were computed for each feeder by considering the tap changing using appropriate mathematical notations. The power losses on each feeder were examined until the minimum voltage drop was obtained. At the minimum voltage drop, the corresponding tap position considered to be optimum tapping position was noted and the corresponding power loss obtained.

The results of the paper showed that the active power losses on the ten selected feeders of Port-Harcourt distribution system had reduced from 2.4MW per feeder to 1.6MW per feeder representing a percentage reduction of 33% after the adoption of the tap changing transformer in the distribution system.

The reactive power losses had equally reduced from 1.28MVAr per feeder to 0.6MVAr per feeder representing a reduction of 86%. For Kaduna distribution system, the active power loss per feeder has reduced from 3.28MW per feeder to 2.47MW per feeder after the tap changing thus representing a percentage reduction of 25%. The reactive power loss per feeder also reduced from 22.4MVAr to 15.0MVAr representing a percentage reduction of 32%. Analysis of the result will assist power system engineers to propose adequate and appropriate maintenance strategies for electric power distribution systems.

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