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From: "Peter Gottlieb"
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Subject: Re: (Avionics) How can this circuit produce an "inductive surge"?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Thu, 03 Oct 2002 04:01:24 GMT
NNTP-Posting-Date: Thu, 03 Oct 2002 00:01:24 EDT
"Richard VanHouten" wrote in message
> > Well, that makes some sense. But running a frequency converting MG set
> > a UPS is not an optimal solution - why not just make the UPS run at the
> > target frequency? The magnetics at 400 Hz are much lighter and
> > than those required for 60 Hz, and the higher frequency makes other
> > practical (eg, resonant).
> The original product was the MG set (an import from Anton Piller Gmbh in
> Germany), the front end inverter was our own design. IBM was
> recommending the Piller MG sets for powering their then-current design
> mainframes, so designing a stand-alone 400 Hz UPS would probably have
> hurt business. The front-end inverter was a stand-by UPS; the MG set
> ran directly off of mains during normal operation. Also, the inverter
> had no magnetics to speak of; the MG set provided the power
I forget that sometimes the business aspects take precedence over the
engineering aspects. That always struck me as being somehow wrong even
though with my business background I understand it.
Yes, I've seen some larger systems with minimal magnetics, which can be done
relatively easily when the bus voltages are high enough. I suppose if you
are relying on the MG magnetics to be closely coupled to the inverter it
would be an "interesting" problem dealing with the direct and reflected
dynamics of the thing.
One of the inverter designs I worked with was a hybrid known as "line
interactive" in that it was neither standby nor on-line but acted
differently under different circumstances. This allowed a simpler and more
reliable system but didn't run the batteries down during a brownout and kept
the unit cool during normal operation. The system was modular so it was
possible to do a quick module replacement while the system was operational.
This and the voltage changing (ie, 480 to 208 etc) meant some significant
One night we had a bet with one of the techs that the small 5 KVA unit could
run all the lighting for the company engineering offices. That transformer
buzzed like one of those old ferroresonant transformers but it did the job.
The voltage waveform looked absolutely horrible though and the unit current
limit had to be bypassed but it ran and it was very cool to hit the off
button and have the entire place go dark.
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