In message <[email protected]>,
dated Tue, 13 May 2014, "ce-test, qualified testing bv - Gert Gremmen"
<[email protected]> writes:
The point is that creepage distances are
determined such as that within the limits of pollution degrees 1-3 , no
substantial leakage current(eventually leading to breakdown of the
insulation) develops. Yes the reaction starts immediately
(salt/electrodes) but the deterioration takes time.
Testing with carbon would lead to infinite creepage distances.
The document you cite admits the presence of conductive pollution
Pollution degree 3
Conductive pollution occurs or dry non-conductive pollution occurs which
becomes conductive due to condensation which is to be expected.
–
Pollution degree 4
Continuous conductivity occurs due to conductive dust, rain or other wet
conditions.
In the past, when commutator motors were widely used, carbon dust
pollution was very common. Infinite creepage distances were not
required.
Apparently the relation between voltage and insulation deterioration
was derived very experimentally .... read here:
In Table 2J, the transient voltages are specified as peak. In Table 1
(of a different standard), the 'rated' [sic] impulse voltages are not
specified as peak so, under IEC rules, are to be taken as RMS. This is
confusing.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
-
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