Doug, You are correct in that the issues we are dealing with are a part of
the Low Voltage installation (up to 600Vac and 1000Vdc in North America, higher
in Europe) wherein all of the common equipment resides.
Having been a part of the US/TAG to IEC SC28A and now IEC 109
technical committees I am quite familiar with Insulation Coordination in Low
Voltage equipment.
The issues are exacerbated with voltage. Medium voltage
distribution (about 12kV to 75kV or so) has its own issues and Hi Voltage
transmission (above 75kV to 1MV here in the US) even more issues. The IEEE
transactions on Dielectrics have continuously dealt with these issues over the
years. Hopefully you have tried to keep up.
Dr Klaus Stemper, as chairman, brought technical discipline to
the work resulting in substantial improvement in the IEC 60664 series (it was
one volume when I started). It also brought a lot of complexity which the
follow-on teams have tried to again simplify for ease of use.
Thanx for the chance to reminisce.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
IEEE Life Fellow
<mailto:[email protected]> [email protected]
From: Doug Powell <[email protected]>
Sent: Wednesday, August 15, 2018 1:40 PM
To: Pete Perkins <[email protected]>; EMC-PSTC <[email protected]>
Subject: Re: [PSES] hipot test
Pete,
Your statements may be true for many product types certified to 60950-1,
61010-1, etc. However when dealing with power conversion products that have
secondary voltages well above mains voltages, this is no longer true. In the
region of 5,000 V and above, corona is a common occurrence in inhomogeneous
fields and this has the effect of causing surface damage (carbonization) on
insulation with any organic content. Inorganic insulators such as ceramics and
glass seem to be much less affected.
Such phenomena is mentioned in Klaus Stimper's book, The Physical Fundamentals
of Low-Voltage Insulation Co-ordination.
All the best, Doug
On Wed, Aug 15, 2018 at 10:04 AM Pete Perkins
<[email protected]
<mailto:[email protected]> > wrote:
All, This discussion goes around year after year.
The test results reported – especially Nute – show that it takes
dozens, maybe hundreds of hipot tests to damage adequate insulation.
In the UK, so I hear, the gov’t safety folks expect each piece
of equipment to be hipot retested annually to demonstrate adequate insulation.
We don’t hear a large hue and cry about failing equipment in that arena.
So from the experience and the data it is clear that both the
engineering type hipot testing and the factory routine testing should not pose
any problem to properly designed and manufactured products.
For line connected products it is foolishness to remove
components for hipot testing. If that is being done the product is not robust
enough in the first place. This includes DC line powered equipment since so
much DC power is being installed and used in places where it is subject to the
same lighting and starting impulses traditionally seen on AC line operated
equipment.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
IEEE Life Fellow
<mailto:[email protected]> [email protected]
From: Jim Hulbert <[email protected] <mailto:[email protected]> >
Sent: Wednesday, August 15, 2018 5:25 AM
To: [email protected] <mailto:[email protected]>
Subject: Re: [PSES] hipot test
I disagree with your NRTL. If the hipot test can degrade the insulation (we’re
talking about a single test on the production line), then the insulation system
is not up to par.
Jim
From: Nyffenegger, Dave [mailto:[email protected]]
Sent: Wednesday, August 15, 2018 12:18 AM
To: [email protected] <mailto:[email protected]>
Subject: Re: [PSES] hipot test
The NRTL I typically use always runs the hipot test for 60 seconds for type
testing during product certification. The listing reports always specify a 1
second hipot for production line testing 100% of all units. Their claim is
that the hipot can degrade some insulation and should be kept to a minimum.
-Dave
From: Richard Nute [mailto:[email protected]]
Sent: Tuesday, August 14, 2018 5:34 PM
To: [email protected] <mailto:[email protected]>
Subject: [PSES] hipot test
Hi Doug:
I've always viewed the purpose of hipot testing as verification only. During
engineering type testing, it is design verification.
I disagree. The hi-pot test determines the minimum electric strength of the
insulation system. Design is an indirect measure of electric strength by
selecting the distances through solid and air (clearance) insulations.
However, design rarely includes the shape of the electric field, which is a
parameter that determines electric strength.
Since hipot is so stressful to insulation…
Again, I disagree. If the design is “good” (adequate electric strength), then
the hi-pot test does not stress the insulation system. See Agilent
Technologies Optocoupler Input-Output Endurance Voltage Application Note 1074.
Best regards,
Rich
From: Doug Powell <[email protected] <mailto:[email protected]> >
Sent: Tuesday, August 14, 2018 1:50 PM
To: [email protected] <mailto:[email protected]>
Subject: Re: [PSES] X & Y Cap rating due to hipot test
I've always viewed the purpose of hipot testing as verification only. During
engineering type testing, it is design verification. During routine testing
for manufacturing, it is workmanship and build verification.
During type testing many safety standards will ask for hipot verification at
various stages, after thermal/humidity tests, after abnormal operations, etc.
Since hipot is so stressful to insulation, it is possible to introduce latent
failures in the test sample after performing multiple hipot tests, combining
many hipots into one is allowable by many inspectors.
During routine testing, a brief hipot is added at the end of the manufacturing
cycle to ensure wire routing is correct (spacings are maintained), integrity of
insulation is maintained, in cases where vibration testing is involved a test
for chafing of wire insulation and so on. Most safety standards have provision
for "allowable disconnects" during the hipot such as surge suppressors and the
like. Also, hipot of sub-assemblies in lieu of the finished assembly if it can
be shown that the test is representative.
Best to all, Doug
--
Douglas E Powell
[email protected] <mailto:[email protected]>
http://www.linkedin.com/in/dougp01
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Attachments are not permitted but the IEEE PSES Online Communities site at
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http://www.linkedin.com/in/dougp01
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