DC voltage testing is commonly used for testing of electrical equipment and apparatus. DC voltage testing has advantages and disadvantages which vary in importance with the specific circumstances.
The advantages and disadvantages of DC voltage are summarized below.
DC test is preferred on equipment whose c • harging capacitance is
very high, such as cables.
• DC voltage stress is considered much less damaging to insulation
than AC voltages.
• Time of voltage application is not as critical with DC voltage as with
• Test can be stopped before equipment failure occurs.
• Measurements can be taken concurrently.
• Historical data can be compiled and made available for evaluation.
• It is not necessary to make a separate insulation resistance test prior
to making a DC overpotential test.
• Size and weight of equipment is significantly reduced compared to AC voltage test.
Stress distribution for transformers, motors, and generator winding
is different for DC voltage than is for AC voltage.
• Residual charge after a DC voltage test must be carefully discharged.
• Time required to conduct a DC high-potential (hi-pot) test is longer
than for an AC hi-pot test.
• Literature governing DC testing of cables suggest possible harmful
effects hi-pot DC testing may have on some types of cables.
• Defects, undetectable with DC, can cause failure under AC voltage test.
• Voltage may not stress uniformly the insulation system.
• Temperature and voltage dependence of resistivity.
• Space charge formation—future potential failures.
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