Analysis and Design of an Electronic On-Load Tap Changer Distribution Transformer for Automatic Voltage Regulation

Current solutions for voltage regulation close to the consumers usually require technicians for manually changing the taps of the transformer, which may entail high maintenance costs and uncontrolled voltage levels. In this context, electronic on-load tap changers (OLTCs) are a prospective solution for present-day and future power grids, since they provide automatic voltage regulation. This paper presents the analysis and design guidelines for an electronic OLTC applied to a distribution transformer, encompassing the physical layout design for external access to the transformer tap terminals, the evaluation of current and voltage transients during the commutation process, and the dimensioning of the electronic switches and protection system. The dielectric withstand of the proposed physical layout is also analyzed through the finite-element approach, guaranteeing adequate insulation for the electronic circuits located outside the transformer tank, which facilitates circuitry maintenance and provides high modularity. The electronic switches and the protection circuit of the electronic OLTC are experimentally tested under normal and faulty operational conditions in a 5 kVA, 7.69 kV/220 V, single-phase earth return distribution transformer.