Comparing the Dielectric Strength of
different materials.
The two major considerations when comparing the
published dielectric strength of different materials are:
a)
the thickness of the test specimen
b)
the test temperature.
The test results can be drastically different if
these two conditions are not identical for the products being compared.
Normally
the standard test calls for a specimen thickness of 1/8" (125 mils) tested at
room temperature (220C) and the result is expressed in volts/mil.
Occasionally it is necessary to generate application specific test results at
some other temperature and these are the results shown on technical data sheets.
The following rules of thumb are applicable to Epoxy and Polyurethane compounds:
-
Unfilled materials (materials that do not contain any fillers such as silica)
almost always are higher in dielectric strength than those containing fillers.
-
A
thinner test specimen will yield higher results and visa versa.
-
The
higher the test temperature the lower the volts/mil.
-
Rigid
materials yield higher volts/mil than softer products.
There are
certain cases, such as with very low viscosity impregnating compounds or coating
materials where standard the test method because it is impossible to cast 125
mil test specimens with good integrity. In these cases copper specimens are
coated to a 1mill thickness for the test.
As
another rule of thumb, the average dielectric strength for epoxies and
polyurethanes are as follows:
-
Flexible materials typically fall between 350 - 400 volts/mil.
-
Rigid
materials are usually between 450 - 500 volts/mil.
There is
a method to estimate the dielectric strength for any thickness of the same
material provided that an accurate dielectric strength is known along with
specimen thickness that was used to obtain it. This can be done using the
formula developed by Carl J. Tautscher as follows;
VxPm = Vpm √ t
√tx
Where
Vpm = Dielectric strength at thickness t in mils.
Vxpm = Dielectric strength at thickness tx in mils.
t = The thickness of the known test specimen.
tx = The thickness in mils of the insulation for which the strength is to be
calculated.
In
general, it is imperative that both the sample thickness and the test
temperature is known for each product in order to compare the dielectric
strengths in a meaningful way.
Disclaimer: The above information is general in nature and is based solely on experiences by Crosslink Technology Inc. The recommendations provided herein may not be applicable in all situations. They are provided to the recipient as part of our customer service and the user must determine the relevance of the information to his/her application, considering any limitations that may be applicable thereto. Crosslink technology Inc. does not accept any liability for direct or consequential damages resulting from the implementations of these recommendations or the use of this information.
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