As an aside, when you come to CDNs for DC systems, things can become
more complicated and interesting.
The AMD1 came about after the US National Committee commented "“The
method for testing DC products in the current revision of IEC61000-4-5
is causing many field related problems for test labs and manufacturers.
Many products will not power up through the power CDN in the standard
and in some cases may be damaged by the
inductance that is necessary to apply the surge."
It is easy to understand why. The large series inductance of the CDN
presents a high pulse impedance, which prevents rapid changes of
current, which is abnormal to the normal system configuration.
Electronic loads like converters and inverters expect a reasonably low
impedance supply to start and operate.
AMD1, in the body text, allows the use of a larger current-rated CDN
with ratings ≤125 A and in Annex I (informative), Issues relating to
powering EUT’s having DC-DC converters on their inputs, suggests a
damping circuit for reducing possible oscillations.
Example CDN component values can be found by searching for papers like
"Influence of Power-Line Coupling/Decoupling Network on Output
Characteristics of the Combination Wave Generator" and "Coupling and
decoupling network for surge immunity test on power lines"
In such a DC system using a CDN whose values force the majority of the
surge stress on the EUT can result in unrealistic surge conditions. The
ITU-T currently opts for a two way approach. Existing CDN arrangements
are grandfathered while giving the test option of using a CDN with
values that reflect the longest connecting cable thus implementing a
system surge test rather than an individual equipment surge test. The
ITU-T has devised an interesting test circuit that imposes a common-mode
surge on both supply polarities. Any system polarity earthing and the
presence of any voltage limiting functions condition the resultant surge
on the system to be common-mode, differential mode or a mixture of both.
Regards,
Mick Maytum
Safety and Telecom
Standards
mjmay...@gmail.com
https://ict-surge-protection-essays.co.uk/
------ Original Message ------
From: "David Schaefer" <david.schae...@element.com>
To: EMC-PSTC@listserv.ieee.org
Sent: 02/04/2019 20:40:24
Subject: Re: [PSES] IEC 61000-4-5:2014/AMD1:2017 - Using the correct CDN
for AC mains testing
A higher current rated CDN can be used, but only if it meets the lower
current CDN’s waveform requirements. From the quoted section:
“Any higher current rated CDN can be used if it meets the specification
requirements in Table 4 for the relevant lower current rating of the
EUT (for
example: a CDN rated 64 A can be used for testing an EUT rated at 5 A,
if it meets the specification requirements of a 16 A rated CDN).”
The reason for this is higher current CDNs are allowed to have pulse
widths significantly shorter than lower ratings. Check out Table 4 of
the 2014 edition. A 16 amp CDN differential mode pulse width is
required to be 50 us +/- 10 us. A 125 Amp CDN is 50 us +10 us/-30 us.
So yes, a 64 amp CDN can be used with a 5 amp product, if it meets the
50 us +/- 10 us requirement.
Thanks,
ELEMENT__15px.jpeg
David Schaefer
Department Manager, EMC
Element Materials Technology
9349 W Broadway Ave
Brooklyn Park, MN 55445, United States
O +1 612 638 5136 ext. 4003
david.schae...@element.com
www.element.com
LINKEDIN.jpeg
<https://www.linkedin.com/company/element-materials-technology/>
TWITTER.jpeg
<https://twitter.com/ElementTesting/>
<https://www.element.com/about-element/growth-acquisitions/exova-group-plc>
From: John Woodgate [mailto:j...@woodjohn.uk]
Sent: Tuesday, April 2, 2019 2:12 PM
To:EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] IEC 61000-4-5:2014/AMD1:2017 - Using the correct
CDN for AC mains testing
I think you did (answer your own question). The text you quote seems
surprisingly (and gratifyingly) lucid. Under 16 A use a 16 A CDN. Over
16 A up to 32 A, use a 32 A CDN.
Best wishes
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2019-04-02 19:14, Richard Georgerian wrote:
Greeting colleagues,
Hopefully, someone in the PSTC group can correct my rational below and
enlighten me on the finer points of CDNs.
The discussion within our applications group is, shall the EUT current
rating be correctly matched to the CDN current rating? For example,
don’t use a CDN rated for 32 A for a EUT that is rated for 2 A, to
ensure that the correct Surge waveform will be applied to the EUT. I
cannot think of a good rational why a CDN rated for 32 A cannot be
used for a EUT rated for 2 A. We do understand that for the different
current ratings of CDNs, 16 A, 32 A, 63A and 125 A, the internal
components must have different values to meet the Surge waveform, for
Open circuit and Short circuit. However, testing Open circuit and
Short circuit on a CDN is without applying any currrent through the
CDN, so in effect, the Surge waveform for a 16 A CDN and a Surge
waveform for a 32 A CDN should have the same effect on a EUT drawing
only 2 A of current.
Probably two questions would help in trying to explain what our
discussion is about.
Must we use a CDN rated for 32 A, for products with a current rating
between 16 A and 32 A, to be considered being compliant to IEC
61000-4-5, for AC mains surge testing?
Must we use a CDN rated for 16 A, for products with a current rating
less than or equal to 16 A, to be considered being compliant to IEC
61000-4-5, for AC mains surge testing?
In the IEC 61000-4-5:2014, Section 7.3 Test setup for surges applied
to EUT power ports –
“The selection of the CDN specification from Table 4 shall be made to
match the current rating of the EUT (for example: an EUT rated at 5 A
shall be tested using a CDN complying with the
specifications of a 16 A rated CDN). Any higher current rated CDN can
be used if it meets the specification requirements in Table 4 for the
relevant lower current rating of the EUT (for
example: a CDN rated 64 A can be used for testing an EUT rated at 5 A,
if it meets the specification requirements of a 16 A rated CDN).”
So maybe I answered my questions.
Thank-you,
Richard Georgerian
Applications Engineer
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