Two-Stage Battery Energy Storage System Sizing for Distribution Transformer Overload Management

Distribution transformers are one of the critical components of a distribution network involving huge capital investments and requiring special care to be ensured during their operation. Overloading of distribution transformers must be avoided beyond a certain threshold after which the capital-intensive process of their augmentation or replacement becomes inevitable. The cumulative peak demands of many distribution transformers contribute to the feeder peak and conditions of overloading lead to costly peak power purchases. Increasing penetration levels of distributed solar photovoltaic power on distribution transformers is also adding to the stress in the form of sudden variations in the net-load. Installation of battery energy storage systems at the secondary side of distribution transformers can provide a lot of techno-economic benefits in mitigating these conditions. This paper presents a two-stage approach for sizing such a system for one of the selected distribution transformers on an actual distribution feeder operational in Delhi, India. The intended application is overload management and peak shaving. The results of the preliminary sizing stage are rigorously tested against different sensitivity scenarios in terms of the number of continuous overloading instances in a year. In the advanced stage, the charge rate and the total amount of unmet energy are used as a feedback to fine tune the size so as to optimally meet the application.