So how do you filter out the harmonics?
Carl
KM1H
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <amps@contesting.com>
Sent: Friday, September 20, 2013 2:41 AM
Subject: Re: [Amps] Re Direct rectification of AC mains to derive the amp,
VDD, supply
On 9/19/2013 1:52 PM, Bill Turner wrote:
Just one question: What is the voltage relationship between neutral and
each
side of the 240 V lines?
In North America, single-phase 240V is fed by a center-tapped transformer,
where you get 240V end to end, and 120 V from either end to the neutral,
which is connected to the center tap. In a breaker panel that has 240V
single phase, half of the 120V breakers are fed from one end of the
transformer, and half from the other. Load that need 240V get only the two
phase lines (the two ends of the transformer).
As Peter Voelpel notes, much of EU, especially those countries whose
infrastructure was heavily destroyed in WWII, have settled on 3-phase to
many (most?) customers. That's harder in counties that have not suffered
that destruction -- there's so much legacy system there, and it's nearly
all single phase.
What DOES happen a lot in the US, both in mixed residential and light
industrial districts of cities and even out here in the Santa Cruz
Mountains, is a bastard system called "high leg Delta," where the basic
distribution is 240V Delta, but with one side of the Delta having a
center-tapped secondary. The center tapped side feeds the 240V
single-phase customers, all three phases feed those larger users who need
it. The MAJOR downside of high-leg is that all of the harmonic current
goes to ground via the neutral fed to single-phase customers, so we suffer
from a TON of buzz (triplen harmonics of 60 Hz -- 180 Hz, 360, 540, 720,
etc. I've measured an amp or more of this harmonic current in both here
in the mountains and in Chicago.
There's a discussion of this in the tutorial I referenced.
73, Jim K9YC
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