Extension of Distribution Transformer Life in the Presence of Smart Inverter-based Distributed Solar Photovoltaic Systems

Abstract

A transformer is an essential but expensive power delivery equipment for a distribution utility. In many distribution utilities worldwide, a sizable percentage of transformers are near the end of their designed life. At the same time, distribution utilities are adopting smart inverter-based distributed solar photovoltaic (SPV) systems to maximize renewable generation. The central objective of this paper is to propose a methodology to quantify the effect of smart inverter-based distributed SPV systems on the aging of distribution transformers. The proposed method is first tested on a modified IEEE-123 node distribution feeder. After that, the procedure is applied to a practical distribution system, i.e., the Indian Institute of Technology (IIT) Roorkee campus, India. The transformer aging models, alongside advanced control functionalities of grid-tied smart inverter-based SPV systems, are implemented in MATLAB. The open-source simulation tool (OpenDSS) is used to model distribution net-works. To analyze effectiveness of various inverter functionalities, time-series simulations are performed using exponential load models, considering daily load curves from multiple seasons, load types, current harmonics, etc. Findings show replacing a traditional inverter with a smart inverter-based SPV system can enable local reactive power generation and may extend the life of a distribution transformer. Simulation results demonstrate, simply by incorporating smart inverter-based SPV systems, transformer aging is reduced by 15% to 22% in comparison to SPV systems operating with traditional inverters.