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> 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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