Power transformer manufacturer

When 50 kva pole mount transformer, test voltage There are several methods of measurement?
(1) Low-voltage measuring transformers in the test 500kva power transformer;
(2) measuring the voltage transformer;
(3) with high voltage electrostatic voltage measurement;
(4) Measure the clearance with the ball;
(5) with a capacitive voltage divider measurement.
(6) Farady oil immersed transformer connection Group Using Y yn0 and D yn11 coupling characteristics