INTRODUCTION
AC testing disadvantages
1. Again, since AC cannot charge the item under test, reactive current is constantly
flowing. In many cases, the reactive component of the current can be much greater
than the real component due to actual leakage. This can make it very difficult to
detect products that have excessively high leakage current.
2. The Hipot has supply reactive and leakage current continuously. This may require a
current output that is actually much higher than is really required to monitor leakage
current, and in most cases is usually much higher than would be needed with a DC
tester. This can present increased safety risks as operators are exposed to higher
currents.
DC testing characteristics
During DC Hipot testing the item under test is charged. The capacitance that causes
reactive current in AC testing will now result in charging current, which exponentially
drops to zero during DC testing.
DC testing advantages
1. Once the item under test is fully charged the only current flowing is the true leakage
current. The DC Hipot tester clearly displays only the true leakage of the product
under test.
2. Since the charging current only needs to be applied momentarily, the output power
requirements of the DC Hipot tester can typically be much less than what would be
required in an AC tester.
DC testing disadvantages
1. Unless the item being tested has virtually no capacitance, it is necessary to raise the
voltage gradually from zero to the full test voltage. The more capacitive the item
the more slowly the voltage must be raised. This is important since most DC Hipots
have failure shut-off circuitry, which will indicate a failure almost immediately if
the total current reaches the leakage threshold during the initial charging of the
product under test.
2. Since a DC Hipot does charge the item under test, it becomes necessary to discharge
the item after the test.
3. A DC Hipot test only charges the insulation in one polarity. This becomes a
concern when testing products that will be used with AC voltages. As such, some
safety agencies do not accept DC testing as an alternative to AC testing.
4. When performing AC Hipot tests, the product under test is actually tested with peak
voltages that the Hipot meter does not display. This is not the case with DC testing
since a sine wave is not generated when testing with a DC voltage. In order to
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