Control of OLTC distribution transformer addressing voltage regulation and lifetime preservation

The containment of voltage variation within admissible ranges is one of the most challenging power quality issue to address in modern low voltage distribution networks. This is due to the widespread use of highly intermittent distributed generators as well as the increasing presence of some types of loads which imply severe variability (e.g., plug-in electric vehicles). The complexity of the voltage regulation is also emphasized by the integration of different devices able to participate at the voltage regulation. An emerging solution is the use of on-load tap changers for the transformers supplying low voltage networks. Due the high fluctuation of the voltages, the main drawback in using the on-load tap changer is the increased number of operation and the corresponding reduction of the lifetime duration. To address this issue, in this paper a new technique is proposed which allows controlling the on-load tap changer by improving the network voltage profile and, at the same time, preserving the lifetime of the tap changer. To do that, a control strategy is formulated in terms of optimization problem whose objective is the minimization of bus voltage fluctuation while limiting the number of operation of the tap changer and satisfying other constraints related to the network and its components. The results of a numerical application are reported and discussed to show the feasibility of the proposed approach.