Material group IIIb
CTI < 175
The usual values for IGBT modules are either material group IIIa or, less commonly,
group II. High-voltage modules often have CTI values within group I and usually fall
within group II as aminimum.
Once the degree of contamination, the relevant voltage and the material group have
been determined, the standards can be used to determine the minimum creepage
distance. For example, for a degree of contamination of 2, a voltage of 400V and
material group IIIb, the creepage distancewill be at least 4mmwith functional insulation
according to standard IEC 60664-1. There is no dependence like that required for the
clearance from the altitudeof use.
Datasheets for IGBT modules usually include information about the clearance and
creepage distances between the individual connections and between them and the
baseplate. Some examples are shown i
formodulesmanufactured by Infineon
Technologies. The values shown here and in other datasheets usually exceed the
minimum distances prescribed in the standards, as clearly shown by the example of the
1.7kVmodule FF650R17IE4, which is designed for 1.7kV, but meets distances similar
to those required for a3.3kVmodule.
Module voltage class
Clearance and creepage distances of selectedmodules
The IGBT module clearance and creepage distances given in the datasheet
always relate to the module when it is unmounted. Mounting the module on a heatsink
can reduce these distances, depending on the design and shape of the mounting bolts
used. Connecting the DC-link bus bars and the load terminals may also reduce the
2.8.2 Insulation voltage
IGBTmodule datasheets normally include information about the insulation voltage U
This voltage value is applied between all short circuited external connections of the
module (including both the auxiliary and the power connections) and the baseplate as
inwhich adual IGBTmodule is usedas an example. If themodule is
a variant which does not have a baseplate, the measurement is taken opposite the
metal exterior coating of theDCB.