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Properties of Insulating Materials
9.6 Properties of Insulating Materials
An insulating material typically has the following properties.
• Resistance varies by temperature
Resistance decreases as temperature increases. In order to diagnose deterioration
due to the change in insulation resistance over time, resistance measured at the
same temperature or resistance for which temperature has been compensated
must be used.
• Resistance varies by measurement voltage
Resistance decreases the higher the applied voltage for measurement. Because
of this property, you must measure the object with a voltage that is greater than or
equal to the voltage used by the object.
• Resistance decreases with absorption of moisture
Resistance decreases by a large degree under high humidity conditions. For this
reason, resistance may be exceptionally low in rainy conditions. In addition, if
condensation has formed on the insulating material, insulation resistance cannot
be measured because a large current will leak on the surface of the insulating
material.
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