Hi Ged:
> "In transformers with REINFORCED INSULATION or DOUBLE INSULATION the
> insulation between 1ary and 2ary windings shalll consist of -
> - 1 insulation layer having thickness at least 1mm, or
> - at least 2 insulation layers with total thickness not less than 0.3mm, or
> - 3 layers provided each combination of 2 layers can withstand the
> dielectric strenght test for REINFORCED INSULATION"
>
> Can anyone explain ther rationale behind these requirements ?
Thin insulation is presumed to be subject to
pin-holes.
If 1 layer of insulation, then the insulation
must be "thick" rather than "thin," hence 1 mm
thickness. We presume no pin-holes in "thick"
insulation, and the insulation comprises
reinforced insulation.
If 2 layers of thin insulation, then presume
a pin-hole in one layer, and that the pin-hole
will not overlay a pin-hole in the other layer.
If that pin-hole is 0.15 mm, then we know that
the air in that pin-hole will at least withstand
the mains voltage. Therefore, the construction
still has two insulations in series, one being
the 0.15 mm air of the pin-hole, the other being
the 0.15 mm thick solid insulation. The 2
insulations in series comprise double insulation.
If 3 layers of thin insulation, then presume
a pin-hole in one layer, and that the pin-hole
will not ovelay a pin-hole in the adjacent
layer. The remaining 2 layers comprise double
insulation.
(In IEC 60960, the requirement for 1 layer in
a 2-layer system is 0.4 mm thickness.)
Best regards,
Rich
ps: I'm not certain of my explanation for 2
layers. This rationale came from 60950,
and I have applied it to 60601.
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