The recognition of possible measurement errors in D-C dielectric testing in the field

IN RECENT years, a definite trend appears to have developed, toward d-c testing of insulation. The reasons or this trend are as follows: 1. The d-c test set required is much more portable than an equivalent a-c test set and power requirements are much less. 2. High-voltage d-c tests are less destructive than equivalent a-c tests, as evidenced by the much flatter voltage-time endurance curve in the case of direct current. 3. From the d-c tests important information may be obtained which is related to the condition of the insulation. Periodic tests make it possible to follow the insulation deterioration and thereby aid in determining the need of reconditioning steps and estimating life expectancy.