Brian, et al,
Well, the elephant in the room is finally being noticed.
There is a good article in the latest 2015 IEEE EMC Magazine, Vol 2,
Qtr 1: 'Conducted Interference, Challenges and Interference Cases' by F
Leterink & T Nederland of the Netherlands. I commend it to all.
The conclusion: Conducted interference has become increasingly
problematic in the past few years, especially within the 2-150kHz band. The
high penetration of non-linear loads, combined with distributed generation,
will influence the voltage profile, i.e. the power quality. New
technologies will introduce new types of interference. Protection devices
like variators and filter in one equipment will also influence the impact on
neighboring equipment, shunting intentional signals or causing resonances,
resulting in high currents between equipment. Due to the lack of (and
interest in ) standards, the 2-150kHz [band] has become the garbage bin for
power electronics. Communication problems as well as interference problems
are occurring already and are delaying the introduction of systems.
Interference is not caused by some single types of equipment of electrical
such as power drives systems, but relate to a quite large spectrum of
electrical equipment, including intentional signals which also cause
interference challenges.
There are 4 types of mains switching systems which need to be
accounted for as part of the overall electrical system in this.
1) AC-AC switching systems, including e.g. 400 Hz to 50/60 Hz
systems,
2) AC-DC switching systems, e.g. the familiar SMPS for
electronics - including the simple walwarts,
3) DC-AC switching systems, e.g. solar panels feeding the grid,
4) DC-DC switching systems, e.g. internal distributed switchers
within SMPS.
The protections have to be coordinated across all of this equipment.
Having been involved in touch current measurement for years and
watched the growth of the non-linear generators (both in number available
and in higher pk-rms ratios - having seen touch currents with 4x myself and
had reported 6x), I have noted that the high crappiness level of the grid is
increasing.
Product committees need to understand these issues on both the
product safety and EMC side and include appropriate requirements In the
standards to mitigate the interference noted.
In talking to one manufacturer recently who complained that their
VFD motor operated product was tripping some GFCI's and causing use problems
for the equipment, I commented that the sending appliance and the receiving
control GFCI both needed robust filtering to ensure that not only would the
appliance work properly but that they would work together. There is more to
it than just meeting the requirements in place today (weak or none at all);
they seem inadequate. There seems to be enough blame to go around on all
sides.
Welcome to the 21st century and the Smart Grid/Smart Homes/Smart
Electronics.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
[email protected]
_ _ _ _ _
Standard Class A 115V~ GFCI (Ground-Fault Circuit Interrupters) are designed
to TRIP at currents around 6mA. I assume this current is accurately detected
between DC and some harmonic of 60hz. However, it is common knowledge that
GFCIs can false trip or nuisance trip when used with motor speed
controllers, lighting dimmer switches, frequency drives, etc. .
I'm not familiar with UL 943C. Does this standard call out specific immunity
levels, energy and frequency, that GFCI must properly operate at? Are there
published Trip Curves that shows current vs frequency?
Has anyone run across published data showing high frequency trip
characteristics of GFCIs?
We have been burned in the past with nuisance tripping GFCIs when products
with frequency drives ramp start a motor. We are trying to understand
exactly what is causing the GFCI to trip so we can design out the problem in
future products. Any insight, recommendations, or suggestions would be most
appreciated.
Best regards,
The Other Brian
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