EEC SE 7430, Руководство пользователя, Страница: 16 / 106

8
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Weak Insulating Materials
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Pinholes in Insulation
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Inadequate Spacing of Components
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Pinched Insulation
Dielectric Withstand Test; AC verses DC
Please check with the Compliance Agency you are working with to see which of the two types of
voltages you are authorized to use. In some cases, a Compliance Agency will allow either AC or DC
testing to be done. However, in other cases the Compliance Agency only allows for an AC test. If
you are unsure which specification you must comply with please contact our CUSTOMER SUPPORT
DEPT.
Many safety agency specifications allow either AC or DC voltages to be used during the hipot test.
When this is the case, the manufacturer must make the decision on which type of voltage to
utilize. In order to do this it is important to understand the advantages and the disadvantages of
both AC and DC testing.
AC testing characteristics
Most items that are hipot tested have some amount of distributed capacitance. An AC voltage
cannot charge this capacitance so it continually reads the reactive current that flows when AC is
applied to a capacitive load.
AC testing advantages
AC testing is generally much more accepted by safety agencies than DC testing. The main reason
for this is that most items being hipot tested will operate on AC voltages. AC hipot testing offers
the advantage of stressing the insulation alternately in both polarities, which more closely
simulates stresses the product will see in real use.
Since AC testing cannot charge a capacitive load the current reading remains consistent from
initial application of the voltage to the end of the test. Therefore, there is no need to gradually
bring up the voltage since there is no stabilization required to monitor the current reading. This
means that unless the product is sensitive to a sudden application of voltage the operator can
immediately apply full voltage and read current without any wait time.
Another advantage of AC testing is that since AC voltage cannot charge a load there is no need to
discharge the item under test after the test.
AC testing disadvantages
One disadvantage of AC testing surfaces when testing capacitive products. 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.