Medium-voltage distribution feeders in open-loop and closed-loop arrangement

This paper deals with a medium-voltage distribution network. The feeders in the open-loop arrangement are changed to the closed-loop arrangement with the aim to improve reliability of the power supply. The paper focuses on the analysis of transient and steady-state operation in the closed-loop that is established by connecting feeders supplied from two different transformers located in the same transformer substation. The transformers are equipped with the tap changers that can change the amplitude of the 20 kV voltages in steps whilst the phase cannot be changed. The possibilities to control the active and reactive power at both ends of the medium-voltage loop are discussed for the case when only the voltage amplitude can be changed and for the case when the voltage amplitude and phase angle can be changed. A simple algorithm for closed-loop active and reactive control is applied. The results of simulations and field testing performed in a 20 kV network are presented.