Date: Mon, 30 Sep 2013 15:38:37 -0700
From: Tomm V Aldridge <taldridge@gmail.com>
To: Bill Turner <dezrat1242@yahoo.com>
Cc: Amps <amps@contesting.com>
Subject: Re: [Amps] ?Direct rectification of AC mains to drive the
Message-ID:
I think there is confusion between PF and crest factor here. A C input
filter will draw all of its current in pulses around the rectified peaks of
the AC sine wave. The crest factor will be much higher than the 1.414 of a
resistive load and harmonic content is high.
For us at home the implications are some flat topping of the voltage
waveform and the inability to draw full rated power from any particular
outlet. In large buildings with 3 phase distribution, expected neutral
current cancellation is not even close to achievable and fires may result
if CF is not controlled.
KD7QAE
## no confusion at all. You can see that effect at a glance using Duncans
PSUD software.
Its also very easy to measure the pulses using a scope or peak reading dvm
across a miniscule
resistance in series with either the pri or sec of the xfmr.
## Psud software will factor in the xfmr input Z, pri resistance, sec
resistance, how much C used,
Z of wiring between main 200A panel and HC supply, contactor resistance, etc,
etc. Typ pulse current
at the crest of the peak is 3-7 times the average value you measure with a
simple clamp on AC Ammeter.
Now that extreme high pulsed current every 8.3 msecs will depend on a LOT of
stuff. Ditto with the
duration of each pulse. Again that is easy to measure with a scope. The
problem with 3 phase
distribution in large buildings is when 120 vac loads are used.....with lousy
PF. IE: hundreds of PCs
etc, all running on 120 vac..... on a typ 208-120 vac 3 phase setup. If
you instead ran the PCs on 208
single phase, even with each PC having lousy PF, you would not have sky
high neutral current. There would be
no neutral current at all.
### 208 vac between phases 1+2..... 2+3..... 1+3.
120 vac between 1+ N...... 2+N...... 3+N.
## In a typ condo or apartment building etc, to divide the load up, each
floor gets a different pair of phases..+ N.
IE: 1st floor gets Phases 1+2 +N. 2nd floor gets Phases 2+3+N. 3rd
floor gets phases 1+3+N. Then repeat
the sequence for floors 4-99. In a condo, there is NO 240 vac...only 208
available. The base board heaters use
208 v versions....OR they use 240v versions.... which wont get as hot. The
240V stove oven element, when run on 208 will
not get as hot. The 240 vac clothes dryer will not get as hot, etc.
## for systems that are critical, and must see clean power.... and not dirty
distorted power from the street, a harmonic neutralized
SOLA constant V xfmr will transform dirty power into clean power..and also
provide near perfect AC V regulation.
Jim VE7RF
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