High Point represents high potential and is a term used for a specific class of test equipment for electrical insulation.
Hipot testers are the reverse of the continuity tester- it conducts the discontinuity test checking no current flow condition between two points. Hipot tests are conducted to find crushed, or leakage in the insulation, and the Hipot tester is used for the ac dc hipot tester.
Let’s discuss the differences between DC and AC hipot.
AC Hipot Tester
With an ac hipot tester, a long ramp time is usually not needed. The AC testing also has the benefits of checking both polarities of voltage and not requiring to discharge of the DUT after completing the testing. This testing also has its fair share of disadvantages – the test must consider the effects of both real and active currents. When an AC voltage is applied, the flowing current equals the voltage divided by the impedance.
But the impedance is complex as it contains both resistive and capacitive components.
The two components are out of phase with each other and combine in a complex manner to form the total current. As the magnitudes of these compounds can be different, the leakage current of a product with large amounts of capacitance can, with some testers, increase significantly without getting detected by the test.
Dc Hipot Tester
A DC hipot test applies a voltage with gradual steps, commonly known as ramping. It pauses after every increase to allow the capacitance of the DUT to absorb a charge and stabilise. The time needed for the charging current to decay after every step is known as the stabilisation time. The current flowing post the stabilisation time has passed represents the leakage current via insulation.
In case the voltage steps are too large, the sharp rise in charging current when the step gets applied might exceed the high current limit, causing the test to fail prematurely. It is important to carefully match the magnitude and timing of the steps to the characteristics of the DUT.
As a DC hipot test charges the capacitance of a DUT, the charge itself proves to be a hazard to testing personnel. It must be removed after the test is over.
Usually, the hipot tester will automatically discharge the DUT for the same period the test voltage was applied.
The DC hipot tester will use a higher voltage than the AC hipot tester, and the DC hipot test will use the DC voltage, whereas the Ac hipot test uses AC voltage at 50/60 Hz. DC hipot tester provides a more accurate reading of the leakage current as it only reads real current. AC hipot tester, on the other hand, measures total current and does not provide accurate leakage current measurement.
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