Doug,
I wouldn't credit the TC 66 has having MOV component
knowledge, just perceptions.
Since my last message I have sent messages to the Chair
and Secretary of TC 66 wearing my IEC SC 37B chair hat.
I was restrained for a change, merely stating they were
breaking the laws of physics for MOVs rather than crazy! I
suggested that if the 0.9 factor was to work it should be
applied to the nominal voltage not the clamping voltage.
I'll keep you informed of developments if any.
Regards
Mick
On 10/05/2012 15:15, Doug Powell wrote:
Mick,
Sorry I didn't review this email before I just sent my
last. Clearly you see the same problem as I. I have to
wonder if the committee in reviewing this clause only
used data sheets and did not validate in the lab. Or is
it possibly the committee members just missed this?
I would like to suggest the Vclamp we should use this the
8 mS / 10 mS rating. That's mS, not uS.
--
Thanks, -doug
Douglas E Powell
doug...@gmail.com <mailto:doug...@gmail.com>
http://www.linkedin.com/in/dougp01
On Thu, May 10, 2012 at 6:58 AM, Mick Maytum
<m.j.may...@ieee.org <mailto:m.j.may...@ieee.org>> wrote:
Doug,
My previous message gave the IEC rulings - terms
clamping voltage and nominal varistor voltage - for
two specific points on the MOV clamping (clipping)
characteristic.
For completeness IEC 61010-1, ed. 3.0 (2010-06)
defines the following:
*working voltage *
highest r.m.s. value of the a.c. or d.c. voltage
across any particular insulation which can occur when
the equipment is supplied at rated voltage
NOTE 1 Transients and voltage fluctuations are not
considered to be part of the working voltage.
NOTE 2 Both open-circuit conditions and normal
operating conditions are taken into account.
I'm now giving an opinion.
Your (nominal) AC supply is 230V rms. The phase "not
less than twice the working voltage." means the hipot
test is done with an AC value of at least 460 V rms or
650 V pk.
The hipot test voltage of 0.9 times the clamping
voltage of the MOV is clearly crazy, as from your
figures of 710 V clamping voltage and 473 V nominal
varistor voltage, testing at 0.9x710 = 630 V would
cause substantial current in the MOV.
One could skate round this and say that the 1 mA
nominal varistor voltage is the clamping/threshold/
voltage - a new term - and use an MOV or combination
of MOVs to have a nominal voltage of 650/0.9 = 720 V.
Sounds like a letter to the Chair and Secretary of TC
66 is needed to resolve this matter.
Regards
Mick
-
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