IGBT Modules - Technologies, Driver and Application (Second Edition) - page 120

durable, reliable insulation for both domains and appropriate coordination of insulation.
This is achieved firstly by using highly insulating ceramic substrates (DCB) and
secondly by allowing sufficiently large clearance and creepage distances to insulate the
potential-carrying auxiliary andpower terminals from the baseplate.
The relevant standards definedifferent types of insulation:
Functional insulation
Functional insulation represents insulation between conductive parts and is
required simply to ensure that the systemoperates properly.
Basic insulation
Insulation between conductiveparts, which is required for protectionagainst
electric shock.
Supplementary insulation
This is inaddition tobasic insulation. It serves toprotect against electric shock
if thebasic insulation fails.
Double insulation
This termdescribes insulation comprisingbasic and supplementary insulation.
Reinforced insulation
A single insulation systemwhich, by determining relevant standards, offers
protection against electric shock equivalent to that offered by double insulation.
Reinforced insulation does not necessarily consist of a single layer butmay
comprise several layers, although these cannot be tested individually.
Safe isolation
This refers to separation of conductive parts that consists of either double
insulationor reinforced insulation.
The proposed system or sub-systemwill dictatewhich type of insulation should be used.
For example, IGBT drivers often require safe isolation in order to separate the high-
voltage circuit (on the IGBT side) from the low-voltage circuit (on the microcontroller
side). Conversely, functional insulation is sufficient for separating the output phases of
2.8.1 Clearance andcreepagedistances
Clearance describes the shortest distance through the air between two conductive
parts. Accordingly, creepage distance describes the shortest appropriate distance
between two conductive parts along the surface of the insulation between the parts.
This is depicted in
shows an example inwhich another conductive
part has been inserted between the two conductive parts. However, it has not been
connected electrically. The clearance and creepage distances in this case have been
reduced by the distance usedby the part.
Relevant standards for determining the necessaryminimum distances for clearance and
creepagedistances applicable for IGBTmodules andentire systems include:
EN 50124-1
, "Railway applications – Insulation coordination, Part 1: Basic
requirements – Clearances and creepage distances for all electrical and
electronic equipment" and their annexesEN 50124-1/A1 andEN50124-1/A2.
EN 50178
, "Electronic equipment for use inpower installations".
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