Hi Bob:
If there is no insulation failure, the
current increases linearly proportional
to the increase in the test voltage.
If there is an insulation failure, "...the
current... rapidly increases in an
uncontrolled manner."
In other words, if there is an insulation
failure, the increase in current is not
linearly proportionally to the increase in
applied voltage.
This means that the resistance of the
insulation is decreasing non-linearly with
applied voltage.
Failure of solid insulation usually results
in a carbon path through the insulation --
a resistor that increases or decreases in
value as a function of the duration of
applied voltage and as a function of the
value of the applied voltage.
Failure of solid insulation rarely results
in a short circuit, i.e., 0 ohms.
In some cases, if the test is sustained,
the power dissipated in the carbon path can
cause it to open, and the test may appear
to be passed.
Consequently, there is no specific current
that indicates an insulation failure.
Another possible insulation failure is that
of an insufficient clearance. In this case,
the air breaks down and an arc occurs. In
most cases, the tester will detect the arc
current and terminate the test.
Depending on the construction, the arc can
have various currents, from low to high.
A low-current arc can be of a sufficiently
low current that the tester will not trip.
The only way to detect a low-current arc
is to look and listen.
Some testers are specifically designed to
detect arcs for any value of test current.
Best regards,
Rich
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Robert
F.
Keller
Sent: Thursday, November 13, 2008 8:36 AM
To: [email protected]
Cc: Robert Keller
Subject: Current limit for Dielectric Test
Hello Group,
I have a question regarding the Electric Strength test in 60950-1
section
5.2. It says in that section that you have a failure or the insulation broke
down when the current which flows as a result of the application of the test
voltage rapidly increases in an uncontrolled manner. So, is there an exact
current limit at which it is considered to have "shorted"? And if so, is this
printed in any standard?
Any insight in this would be greatly appreciated.
Best Regards,
Rob Keller
Senior Engineer
Communication Certification Laboratory
Ph.: 801.972.6146 Ext.237
Fax: 801-972-8432
[email protected]
-
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at
http://www.ieeecommunities.org/emc-pstc
Graphics (in well-used formats), large files, etc. can be posted to that URL.
Website: http://www.ieee-pses.org/
Instructions: http://listserv.ieee.org/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas <[email protected]>
Mike Cantwell <[email protected]>
For policy questions, send mail to:
Jim Bacher <[email protected]>
David Heald <[email protected]>
