Due to the single-phase loads and their stochastic behavior, the current in the distribution feeders is not balanced. In addition, the single-phase loads are located in different positions along the LV feeders. So the amount of the unbalanced load and its location affect the feeder losses. An unbalanced load causes the feeder losses and the voltage drop. Because of time-varying behavior of the single-phase loads, phase balancing is a dynamic and combinatorial problem. In this research, a heuristic and dynamic solution for the phase balancing of the LV feeders is proposed. In this method, it is supposed that the loads’ tie could be connected to all phases through a three-phase switch. The aim of the proposed method is to make the feeder conditions as balanced as possible. The amount and the location of single-phase loads are considered in the proposed phase balancing method. Since the proposed method needs no communication interface or no remote controller, it is inexpensive, simple, practical, and robust. Applying this method provides a distributed and dynamic phase balancing control. In addition, the feasibility of reducing the used switches is investigated. The ability of the proposed method in the phase balancing of the LV feeders is approved by carrying out some simulations.
The transformers which connect the different voltage levels in transmission and distribution systems are supplied with on-load tap changing mechanism. The on-load tap changer maintains the voltage amplitude within the pre-defined limits at the so called regulation bus. In a radial feeder, the on-load tap changers are cascaded. Poor coordination between cascaded tap changers causes improper voltage profile and unnecessary operations of tap changers. A fuzzy logic controller is presented in this paper which improves the operation of cascaded tap changers as well as parallel ones. The proposed controller monitors both primary and secondary voltages of the transformer and orders an upward or downward tap changing operation. Because of locally measurement, the communication is not required between two substations which are apart. The controller is also able to set the time delay of tap changing operations based on the measured voltages, which improves the performance of controller and provides a chance to reduce the unwanted changes of taps and also an opportunity to correct the voltage in a reasonable time.
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