Hi Gary,
I've written extensively about this in tutorials written for hams, and
also for audio/video installation contractors. They're on my website.
IMO, an extensive discussion is WAY off topic of this reflector.
k9yc.com/publish.htm
The simple fact is that the power drawn by appliances with motors is a
small fraction of the total power for most retail customers. While the
same is true in large buildings, they have enough motor loads to justify
the cost of 3-phase power (mostly for HVAC, but also for elevators,
etc.). Many buildings also use the higher voltages provided by 3-phase
distribution for fluorescent lighting, but wiring to those fixtures is
single phase, and the load current drawn has the same issues with
harmonics as other electronic loads.
As to delta connections -- virtually any transformer or large motor has
stray capacitance between its windings and its enclosure, and that
enclosure is usually bonded to structure, which is grounded. Also, the
power company nearly always uses a system called "high leg Delta" in
neighborhoods where most customers are residential but a few need
3-phase power. 3-phase customers get 240V delta, everyone else get's a
transformer fed by one leg with a center tapped secondary, and the
neutral of that feed carries some of the harmonic current from the loads
of those 3-phase customers.
High-leg Delta is quite common in cities and suburbs, and it's also
feeding me and my neighbors out in the country in the Santa Cruz
Mountains. I've measured as much as 1A on the conductor that grounds my
neutral, and I've measured more than that in recording studios where
there were more industrial users on the same power system. This was a
BIG problem for the recording studio, because the magnetic field from
that current coupled strongly into single-coil guitar pickups and
dynamic mics that lacked hum-bucking coils. Which is why I was there. :)
73, Jim K9YC
73, Jim K9YC
On Sat,8/27/2016 11:20 AM, Gary J FollettDukes HiFi wrote:
3-phase power is not the universal blessing that you believe it to be.
Well, I don’t really think I said it was the universal blessing. I
just said that there is a reason why 3 phase power is used in heavy
power consumption settings with efficiency in mind. There is no room
for argument that a 3 phase RF power generator, operating without
transformers, without filter capacitors is more efficient and less
costly than its single phase counterpart. In addition, the elimination
of filter capacitors reduces heat loss and eliminates the single most
failure prone component in power supplies, the electrolytic capacitors.
The overwhelming bulk of the power delivered to today's homes is to
electronic loads, which draw highly distorted current, resulting in
very high harmonic content. That, in turn, results in high neutral
currents that consist of "triplen" harmonics of the fundamental rate
(50 or 60 Hz). Triplen harmonics are those whose order is a multiple
of 3, and they add in the neutral rather than cancel, even with loads
that are perfectly balanced. Those harmonics also add in the "green
wire," producing the characteristic "ground buzz" (180 Hz, 360 Hz, 540
Hz, 720 Hz, . . . ), as opposed to hum (50/60 Hz).
Neutral currents in 3-phase systems can easily exceed the current in a
phase conductor. Neutral current is what started the very real
"Towering Inferno" and burning insulation running up cable risers
carried the flames.
Does this apply to Delta 3 phase systems that have no neutral?
I am not trying to be confrontational here. As we all should be doing,
I am just trying to learn more as we discuss radio related topics. I
am not right about everything, which is why I am always trying to
learn more.
For example, I am still trying to understand how the power companies
pulled off that scheme of promoting “money saving efficient
appliances”, a multi-year pitch followed by the whining plea to the
PUC for higher per KWh rate to make up for lost sales caused by
massive implementation of more efficient (and often less reliable)
appliances.
This is relevant to radio hobbits because the expenditure of
some capital to make three phase available more widely available would
reduce cost of linear amplifiers and other power equipment.
Gary
On Aug 27, 2016, at 12:30 PM, Jim Brown <k9yc@audiosystemsgroup.com
<mailto:k9yc@audiosystemsgroup.com>> wrote:
3-phase power is not the universal blessing that you believe it to
be. The overwhelming bulk of the power delivered to today's homes is
to electronic loads, which draw highly distorted current, resulting
in very high harmonic content. That, in turn, results in high neutral
currents that consist of "triplen" harmonics of the fundamental rate
(50 or 60 Hz). Triplen harmonics are those whose order is a multiple
of 3, and they add in the neutral rather than cancel, even with loads
that are perfectly balanced. Those harmonics also add in the "green
wire," producing the characteristic "ground buzz" (180 Hz, 360 Hz,
540 Hz, 720 Hz, . . . ), as opposed to hum (50/60 Hz).
Neutral currents in 3-phase systems can easily exceed the current in
a phase conductor. Neutral current is what started the very real
"Towering Inferno" and burning insulation running up cable risers
carried the flames.
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