DC Hi-Pot Test
The DC hi-pot test is normally not made for AC electrical switchgear and therefore may be considered only when AC hi-pot cannot be performed. The hi-pot testing of switchgear involves testing of the circuit breakers and switch- gear buses separately. This is a major test and determines the condition of the insulation of the switchgear assembly. The DC hi-pot test is not preferred for testing AC switchgear because the application of DC voltage does not pro- duce similar stress in the insulation system as is produced under operating conditions. Moreover, the DC hi-pot test produces corona and tracking owing to concentration of stress at sharp edges or end points of buses. The corona and tracking are more pronounced in older equipment, and it is therefore recommended that DC hi-pot testing be avoided on such equipment.
The test procedures for DC hi-pot testing are similar to those of AC hi-pot testing and are described in detail in Chapter 2. If DC hi-pot testing is to be performed, the DC voltage test values shown in Table 7.7 are recommended for various voltage-class equipment.
The hi-pot test should be conducted under conditions similar to those of commercial testing. The switchgear should be wiped, cleaned, and restored to good condition before the hi-pot test is conducted. Temperature and humidity readings should be recorded and the test reading corrected when conducting DC tests.