Joe Randolph and I talked about “pulsed power” delivery at the 2019
ATIS-PEG conference last week and how it should be treated.
A good starting point is the IEC 60479 series of documents on “Effects
of current on human beings and livestock”. IEC 62368-1 mentions the time
locked IEC TS 60479-1:2005, but the current version is IEC 60479-1:2018.
The IEC TS 60479-2:2017 variant is particularly interesting as clause 9
covers “Effects of current pulse bursts and random complex irregular
waveforms”. For sequential pulses separated by > 300 ms there isn’t a
cumulative effect on the heart and each pulse can be treated as single,
non-repetitive pulse of current. For safety, I believe pulsed power
systems will insert this separation time when any non-load currents are
detected to delay any following power pulse.
Thus only the effects of a single power pulse need to be evaluated
provided the safety separation is >0.3 s. Primarily IEC TS 60479-2:2017
is seeking to establish a “no fibrillation” condition, which is higher
stress level than you’d want for a safety standard.
A 2018 ATIS-PEG conference paper on IEC TS 60479-2:2017 gave an example
evaluation using the quoted pulsed currents produced by a TASER® gun.
Safety tip - if anyone is pointing a TASER® gun at you, yell out you
have a pre-existing medical condition.
Regards,
Mick
Safety and Telecom
Standards
mjmay...@gmail.com
https://ict-surge-protection-essays.co.uk/
------ Original Message ------
From: "Joe Randolph" <j...@randolph-telecom.com>
To: EMC-PSTC@listserv.ieee.org
Sent: 12/03/2019 17:54:36
Subject: Re: [PSES] classification of the output
Hi Pete:
This discussion reminds me of some things I have been hearing about
“digital power” as a way to deliver large amounts of power while
keeping the circuit classification to ES1 or ES2. A company called
Voltserver has been promoting (and deploying) this technology.
I know few details about the scheme, and I’m not familiar with how IEC
62368-1 evaluates things such as touch current.
However, as I understand it, the “digital power” method uses a series
of short pulses with off periods during which the power sourcing device
attempts to detect a fault condition. The power is immediately cut off
if a fault condition is detected. I have heard that the pulse
frequency is in the range of 7 KHz, and the voltages can be up to 380
V. The key to making this scheme even plausible is that the system
must respond VERY quickly to a fault condition (such as a human
touching a live conductor).
I’m interested in hearing your thoughts (and hopefully Rich Nute’s
thoughts too) regarding how the touch current tests in IEC 62368-1
might apply to such a system. I don’t know whether such a system would
pass or fail the IEC 62368-1 tests.
Regardless of whether such a system would pass or fail the existing
tests in IEC-62368-1, I think the important thing is to go back to
first principles and evaluate whether the proposed “digital power” can
be made sufficiently safe to prevent harm to humans.
Thanks,
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com
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