[TenTec] Slightly OT: Sunspots for propagation? Who needs 'em?

[Jim Brown]

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 at audiosystemsgroup.com 
>> <mailto:k9yc at 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.
>