I agree, this is off topic now and will read your reference .
Thanks,
Gary
> On Aug 27, 2016, at 1:54 PM, Jim Brown <k9yc@audiosystemsgroup.com> wrote:
>
> 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 <http://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> <mailto: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.
>>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|