just call it 2 phase

Salmon Egg wrote:


Yes -you have it right. The interpoles cancel the effect of the armature reaction only at the segments under commutation - eliminating the need to shift brushes. They also insure that the net induced voltage in the coil under commutation is 0. However they have no effect under the field poles as they act only in a narrow region on the the neutral axis. The distortion under the field poles really wouldn't matter except for saturation which causes the increase in flux on one side of the pole to be less than the decrease under the other side. The result is a weakening of flux under load. This can be partially countered by increasing the field current but,for high armature current or highly variable loads, this distortion has an effect on commutation- tending to increase arcing between segments of the commutator. Interpoles alone don't completely handle this problem. Hence the "compensating winding"- an attempt to cancel out armature reaction mmf. In most machines it is not needed but there are cases where it is very useful and worth the expense.
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True.
I don't recall the name of the winding and my machinery text is packed up somewhere.
The machine was the exciter of a 320MVA turbine generator installed in 1958. It was gear driven at about 900RPM, had a huge amount of brushes and was very hard to keep clean. I think it has been replaced by a pile of electronics.
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Generators are nothing.
In the earlier days of car radios, they used miniature vacuum tubes. Tubes didn't work so well with 6V on the plate, so the radios had things called "vibrators" (no not THAT kind), something that rapidly interrupted or reversed current flow to a step-up transformer, the output of which was rectified to a B+ voltage that tubes could use. Standard filtering of the leads allowed them to work.
I once had a police 2-way radio that used a bunch of 12AT7 class tubes.
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James Sweet wrote:

The DC had some ripple, but it wasn't pulsating. I have looked at the output of a generator on more that one pre '63 car with a scope. One of the first signs of a failing generator was noise in the radio.

BTDT, 40 years ago.
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Thjis is why in my previous post I mentioned that a modern generator would have various bells and whistles that may not haver been present in early Edison generators. A generator is likely to have a rotating brush assembly so that the brushes could be placed where the arcing is minimized. Interpoles will also help commutation. The brush material itself is somewhat resistive to damp out noise a bit.
Remember that in the days of six volt car batteries charged by a dc generator, radios worked just fine.
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Salmon Egg wrote:

If the brushes in Edison's DC generators didn't contact two segments at a time at the current they produced, the arching would destroy the commutator in a few minutes. Just like the similar design of a universal motor, it is the biggest problem with commutated brush type motors or generators.
To intentionally pulse the DC, the gaps between segments would have to be wider than the brush so they would operate in a break before make mode.

I worked on hundreds of them, in the '60s. Have you ever studied the vibrator supply design? There are buffer capacitors across the primary winding of the transformer to reduce the loss of contact material. The vibrators ran at 115 CPS (Hz) to reduce the hum. It was a tradeoff between the cost to filter the DC, the life of the vibrator, and the RF interference caused by the vibrator. The vibrators were in thick steel housings, with a thick molded foam insert to reduce the mechanical noise. The socket had a spring loaded clamp that held the vibrator case tightly to ground it to the chassis to reduce EMI/RFI noise. Even after all that, the life of a vibrator could be as little as a month, if the radio was in a taxi or someone who drove all day with the radio on. The foam deteriorated from the heat and contaminated the contacts, so the shelf life wasn't good, either.
The first solid state replacement vibrators came out in the '60s, built with Germanium power transistors in T)-3 cases, inside a standard vibrator can. If the buffer capacitor was bad, or failed, they blew immediately.
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Michael A. Terrell wrote:

By the time the "mains powered" radios came along, the supply was AC. In addition, while an arcing commutator produces hash, it produces more important problems in large DC machines and the design of the commutation system as well as proper maintainance of the commutator surface eliminates the arcing. Small motors such as used in drills do arc because a) nobody maintains the commutator until the arcing becomes a problem, and b) compensation for armature reaction is not provided.
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Don Kelly wrote:

Some areas still had DC power well into the '60s and even early '70s. A friend of mine in the Army told me what his dad had to go through to get AC for the new elevator in his building near Chicago, around 1970. The elevator company refused to repair the old DC model, and only installed new AC powered elevators. People in those areas used the transformerless radios on the DC power lines, and wouldn't notice the switch to AC, as long as the usual two electrolytics following the rectifier were still good.

Add to that, the crappy speed controls in variable speed power tools, and you get even more noise, because they are too cheap to add a small inductor to filter the noise before it enters the power line and is radiated to nearby electronics.
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Michael A. Terrell wrote:

I read somewhere recently that the last DC service to a building in New York I believe it was, was shut off sometime in the 1990s. I had no idea it lasted so long.
Somewhere there is a website with pictures of some of the gigantic rotary converters used to convert 25Hz AC to DC to drive subway trains. Some of these were still operational at least up to a few years ago. I've seen relatively recent pictures of polyphase mercury arc rectifiers still in operation doing the same job.
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Your date is a little off. The last plug was pulled November 14, 2007. ;-)
http://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/?apage=2
(Geez, Google is worse than even I thought!)
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James Sweet wrote:

There were photos of some multiphase mecrury vapor recitifers from a subway line on alt.binaries.pictures.radio a few years ago.
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Michael A. Terrell wrote:

This is the site I was thinking of http://www.nycsubway.org/tech/power/rotary.html
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On Thu, 26 Mar 2009 01:58:24 -0400 Michael A. Terrell
| Some areas still had DC power well into the '60s and even early | '70s. A friend of mine in the Army told me what his dad had to go | through to get AC for the new elevator in his building near Chicago, | around 1970. The elevator company refused to repair the old DC model, | and only installed new AC powered elevators. People in those areas used | the transformerless radios on the DC power lines, and wouldn't notice | the switch to AC, as long as the usual two electrolytics following the | rectifier were still good.
Some parts of West Virginia had 25 Hz into the late 1950's (my grandfather worked on those). It was there for powering coal mine equipment, but many businesses and homes were connected, as well.
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snipped-for-privacy@ipal.net wrote:

That has been beaten to death on this, and other newsgroups for years. The mine needs power, and builds the plant. The city grows around the mine, and uses the same system. Old news.
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On Wed, 25 Mar 2009 14:03:30 -0400 Michael A. Terrell
| The arcing commutator would generate so much hash that all you would | get would be a loud buzz. Any time the brush loses contact with the | armature, it arcs.
And a filter that can remove 60 Hz (or whatever slow rate was in use back in Edisn's day) could not clean up some modulated noise band at higher freqs?
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snipped-for-privacy@ipal.net wrote:

Did you even read what you posted? That is one of your most pathetic attempts at trolling, to date.
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On Fri, 27 Mar 2009 15:37:54 -0400 Michael A. Terrell
| | snipped-for-privacy@ipal.net wrote: |> |> On Wed, 25 Mar 2009 14:03:30 -0400 Michael A. Terrell
|> |> | The arcing commutator would generate so much hash that all you would |> | get would be a loud buzz. Any time the brush loses contact with the |> | armature, it arcs. |> |> And a filter that can remove 60 Hz (or whatever slow rate was in use back in |> Edisn's day) could not clean up some modulated noise band at higher freqs? | | | Did you even read what you posted? That is one of your most pathetic | attempts at trolling, to date.
Do you even understand filters at all?
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snipped-for-privacy@ipal.net wrote:

Sure, from line frequency up to 11 GHZ. Ever work with Sallen-Key? Butterworth? How about FIR filters, and using them with DSP? How about UHF diplexers that handle over 200 KW? A filter can only do so much with the input, or we would still be using TRF radios. IOW, you can't make a silk purse out of a sow's ear, no matter how much you whine, or how many hissy fits you throw.
The only 'filter' that would work with your ridiculous pulsing DC would be a battery bank or a band of huge electrolytics. The battery would be a better choice, because the electrolytics would heat up quite a bit from all the AC flowing through them.
Those arching brushes would fail every EMI/RFI standard. Do you understand that? Or to make it even simpler for you, it would wipe out all radio & TV OTA signals for quite a distance. If it was a large power plant, it could be a mile or more each side of the HV distribution lines.
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On Sun, 29 Mar 2009 04:09:40 -0400 Michael A. Terrell
| | snipped-for-privacy@ipal.net wrote: |> |> On Fri, 27 Mar 2009 15:37:54 -0400 Michael A. Terrell
|> |
|> |> |> |> On Wed, 25 Mar 2009 14:03:30 -0400 Michael A. Terrell
|> |> |> |> | The arcing commutator would generate so much hash that all you would |> |> | get would be a loud buzz. Any time the brush loses contact with the |> |> | armature, it arcs. |> |> |> |> And a filter that can remove 60 Hz (or whatever slow rate was in use back in |> |> Edisn's day) could not clean up some modulated noise band at higher freqs? |> | |> | |> | Did you even read what you posted? That is one of your most pathetic |> | attempts at trolling, to date. |> |> Do you even understand filters at all? | | | Sure, from line frequency up to 11 GHZ. Ever work with Sallen-Key? | Butterworth? How about FIR filters, and using them with DSP? How about | UHF diplexers that handle over 200 KW? A filter can only do so much | with the input, or we would still be using TRF radios. IOW, you can't | make a silk purse out of a sow's ear, no matter how much you whine, or | how many hissy fits you throw.
Very good. You must have done some Googling to find all those terms.
| The only 'filter' that would work with your ridiculous pulsing DC | would be a battery bank or a band of huge electrolytics. The battery | would be a better choice, because the electrolytics would heat up quite | a bit from all the AC flowing through them.
They do make filters for smoothing out the ripple that comes from converting AC to DC. Ever tried one of those? Most of them are low pass. Raise the frequency and the filtering is more effective.
| Those arching brushes would fail every EMI/RFI standard. Do you | understand that? Or to make it even simpler for you, it would wipe out | all radio & TV OTA signals for quite a distance. If it was a large | power plant, it could be a mile or more each side of the HV distribution | lines.
I never said that arcing brushes would pass EMI/RFI standards. The subject was on the power wiring. A low pass filter would block the higher frequencies on that path. What you do on the antenna connection is anothr matter.
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snipped-for-privacy@ipal.net wrote:

More substandard trolling?

More substandard trolling?

More substandard trolling?
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