contact us
The Dielectric Strength Test: Setup Details That Decide the Result
products
- Main Products
technical articles
Company News
Dielectric strength testing applies a high voltage between an accessible conductive part and the live parts, or between primary and secondary circuits, and requires that no breakdown occurs. The clause is short; the execution has more variables than the clause suggests.
Voltage and duration
The test voltage depends on the working voltage and on whether the insulation is basic, supplementary or reinforced, and it is applied for a defined period, conventionally one minute. Some standards permit a shorter test at a higher voltage for production testing, and the two are not interchangeable: a routine test is not evidence of type compliance.
Ramp and trip current
The voltage should be raised steadily to the test value rather than switched on at full value, because a step can cause a transient that trips the set and looks like a failure. The trip threshold of the test set matters as much: a set that trips at a few milliamps will fail equipment with legitimate leakage through a filter capacitor, and a set with a very high threshold will pass a genuine partial breakdown.
What counts as failure
Breakdown is a sudden collapse of voltage with a rise in current. A slow increase in current without collapse is usually capacitive charging or corona, and it is not a failure. Distinguishing the two requires watching the current throughout the hold rather than only reading the pass lamp at the end.
