Why open circuit test is done on hv?

The open circuit test on high voltage (HV) equipment, such as Transformers, is performed to determine the no-load characteristics and losses of the equipment. During this test, the primary winding is energized while the secondary winding is left open, allowing for the measurement of parameters like no-load current, no-load losses, and voltage regulation. This information helps to assess the efficiency and performance of the transformer under normal operating conditions. Additionally, it provides insights into the core material and design quality.