IEC/IEEE International Standard- Power transformers - Part 21: Standard requirements, terminology, and test code for step-voltage regulators

This document describes electrical, mechanical and test requirements of liquid -immersed, single- and three-phase, 50 Hz and 60 Hz, self and forced -air cooled, distribution, overhead and substation, step -voltage regulators, 1 000 kVA (single-phase units) or 3 000 kVA (threephase units) and smaller, 34 500 volts and below (2 400 V minimum) and their associated controls.