Rich,
As requested here are some comments on the 2nd Edition requirements
IEC 61051 is a generic document. Your ad hoc group studying AC overvoltage
protection might have been better served by the more recent and targeted
document ITU-T K.77: Characteristics of metal oxide varistors for the
protection of telecommunication installations.
Even the K.77 title targets the specific component used - the metal oxide
varistor. Did you know that if you look up the IEV definition of a varistor it
is IEV 151-13-23 varistor: resistor the resistance of which is strongly varying
with the applied voltage. This generic definition could also apply to silicon
avalanche diodes and many other types of voltage limiter. Best be specific in
these circumstances for an International document.
In G.8.3.3 you reference IEC 61643-11, yet in the NOTE you reference the prior
version IEC 61643-1. Is this a mistake? In fact, IEC 61643-1 should have been
IEC 61643-11 anyway, but for an IEC error - CENELEC got the numbering right.
In G.8.3.3 you reference IEC 61643-11 for the test method and compliance
criteria using IEC 61643-11 clauses 8.3.8.1 and 8.3.8.2. However when you
study these there is a time mismatch for the Line to Protective Earth condition
between IEC 62368-1 and IEC 61643-11. IEC 61643-11 Table B.1 – TOV test values
for systems complying with IEC 60364 series specifies 1200 + 1.1 x rated AC
voltage for 0.2 s and not 5 s as IEC 62368-1. Why is the IEC 62368-1 test 25
times longer?
For the Neutral to Protective Earth condition IEC 62368-1 and IEC 61643-11
agree with 1200 V ac for 200 ms, but IEC 61643-11 says "withstand or safe
failure mode acceptable" but IEC 62368-1 says "withstand" only. Why the lack of
harmonization? The source impedance specified in IEC 61643-11 can allow a lot
of current flow in mains rated MOVs.
It might have been beneficial if your ad hoc group liaised with IEC SC37B:
Specific components for surge arresters and surge protective devices for a
sanity check on this misunderstood subject.
Regards
Mick
Richard Nute [email protected], 13 May
Hi Mick:
The "problem" is the one originally described.
The 2nd Edition of IEC 62368-1 is the result of
an ad hoc group that studied the various varistor
components to arrive at a set of requirements that
would allow the varistor (and its derivations) to
perform the intended "clamping" yet not incur a
safety issue.
The big deal here is the issue of the energy the
varistor must dissipate, which can cause catastrophic
failure of the varistor, often resulting in a fire.
The ad hoc group concentrated on requirements that
would prevent device failure. IEC 62368-1 2nd
references IEC 61051 for most requirements.
I'm sure the varistor requirements will be again
reviewed at the upcoming TC108 meeting in June in
Northbrook, Illinois, U.S.A.
If you or anyone on this list would like to review
and comment on the 2nd Edition requirements, send
me an e-mail and I'll send you the draft 2nd Edition
along with a comment form, and who to send it to.
Best regards,
Rich
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