Based on the recommendations given in IS: 4029:1977 decided DC test voltage 

= (2E+1kV) 1.6 * M 

Where E = rated voltage.

 2.6 = AC to DC conversion factor.

M = derator factor which is a function to be decided on the basis of the age and condition of equipment. 

The DC voltage applied in steps and the leakage current recorded at each step. A plot leakage current Vs test voltage is to be plotted as the test progress. 

Some recommendations of IS : 4029 : 1977. 

a. The HV test made on the windings on acceptance shall as far as possible not be repeated. If however a second test to be made at 80% of the voltage given by the empirical formula given above. 

b. Test voltage for completely rewound motor = full test voltage for new motor. 

c. Partially rewound or overhauled motor = 75% * full test voltage for a new motor. 

d. Before the test for the old parts of the winding shall be carefully cleaned and dried. 

e. Before attempting of HV DC test a minimum PI value of motor should be obtained.