MI 3205 TeraOhm XA 5kV
Measurements
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5.2.4 Withstanding Voltage Test
Some standards allow the use of a DC voltage as an alternative to AC withstanding
voltage testing. For this purpose the test voltage has to be present across the insulation
under test for a specific time. The insulation material only passes if there is no
breakdown or flash over. Standards recommend that the test starts with a low voltage
and reaches the final test voltage with a slope that keeps the charging current under the
limit of the current threshold. The test duration normally takes 1 min.
Withstanding voltage test or dielectric test is usually applied for:
Type (acceptance) tests when a new product is being prepared for manufacture,
Routine (production) tests for the verification of safety on each product,
Maintenance and after service tests for any equipment where the insulation
system can be exposed to degradation.
Some examples for DC withstanding test voltage values:
Standard (only sample values)
Voltage
EN/IEC 61010-1 CAT II 300 V (mains circuits) basic insulation
2100 V
EN/IEC 61010-1 CAT II 300 V (mains circuits) reinforced insulation
4200 V
IEC 60439-1 (clearance between live parts…), withstanding
impulse voltage 4 kV, 500 m
4700 V
IEC 60598-1
2120 V
Humidity and insulation resistance measurements
When testing outside the reference ambient conditions, the quality of the insulation
resistance measurements can be affected by humidity. Humidity adds leakage paths
onto the surface of the complete measuring system, (i.e. the insulator under test, the test
leads, the measuring instrument etc). The influence of humidity reduces accuracy
especially when testing very high resistances (i.e. Tera ohms). The worst conditions
arise in environments containing high condensation, which can also reduce safety. In the
case of high humidity, it is recommended to ventilate the test areas before and during
the measurements. In the case of condensed humidity the measuring system must dry
and it can take several hours or even few days to recover.
