Distribution Transformer

Overview

A distribution transformer steps medium voltage down to the utilization voltage delivered to homes and businesses, the final voltage-conversion stage in the power-distribution chain. This 500 kVA oil-immersed unit transforms 11 kV to 433 V at 50 Hz and mounts on a pad or pole near the load it serves. Energy transfers between windings through a shared magnetic core by electromagnetic induction, with no moving parts.

Construction

At the heart of the unit is the Active Part Assembly: the laminated silicon-steel core and the concentric high- and low-voltage windings that link through it. The grain-oriented core laminations minimise eddy and hysteresis losses, while the copper or aluminium windings are wound to the turns ratio that sets the voltage transformation.

The active part is submerged in the Tank, a sealed steel vessel with external radiator fins that provide the cooling surface for ONAN (oil natural, air natural) operation. The tank is filled with Insulating Mineral Oil, mineral insulating fluid that serves two roles: it insulates the windings and core, and it carries heat by convection from the active part to the tank walls.

Connections pass through the Bushing Set, porcelain or polymer insulators that bring the HV and LV terminals through the tank lid without compromising the seal. The Off-Load Tap Changer allows the HV turns ratio to be adjusted in discrete steps to compensate for supply-voltage variation; on this unit it is the off-load type, set with the transformer de-energised.

Supporting hardware includes the Accessories (oil-level gauge, breather, pressure-relief device, and drain valve), the Grounding Terminal earthing studs for the tank and neutral, the Mounting Bracket for pad or pole fixing, and the Rating Nameplate recording ratings and connection data.