Lighting transformers serves as isolation between primary and secondary, it also restricts any high voltage spikes. It also restricts short circuit current in the load and saves major accidents.
16kVA to 500kVA
As per IS: 2026 (part 4)
Off load tap changer
IS: 1180/IS: 335/IS: 2066/IS: 3347 OR: IEC: 60076