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Cooking Equipment (rec.food.equipment) Discussion of food-related equipment. Includes items used in food preparation and storage, including major and minor appliances, gadgets and utensils, infrastructure, and food- and recipe-related software. |
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in article , Adder at wrote
on 12/10/04 2:14 PM: > Multipole generators can do this, maybe they had not heard of more than 2? > poles back then I must admit that I do not know for sure, but multipole alternators probably came before the electrification of Niagra. Hydraulic turbines could not spin at synchronous speed. The trouble with multipole alternators is that they will be larger. Because they turn slowly, they require more torque for the ame amount of power and, therefore, must be built more ruggedly. Bill |
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"Repeating Rifle" > wrote in message ... | I must admit that I do not know for sure, but multipole alternators probably | came before the electrification of Niagra. Hydraulic turbines could not spin | at synchronous speed. | | The trouble with multipole alternators is that they will be larger. Because | they turn slowly, they require more torque for the ame amount of power and, | therefore, must be built more ruggedly. http://www.antiquewireless.org/otb/60cycles.htm N |
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"Repeating Rifle" > wrote in message ... | I must admit that I do not know for sure, but multipole alternators probably | came before the electrification of Niagra. Hydraulic turbines could not spin | at synchronous speed. | | The trouble with multipole alternators is that they will be larger. Because | they turn slowly, they require more torque for the ame amount of power and, | therefore, must be built more ruggedly. http://www.antiquewireless.org/otb/60cycles.htm N |
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"Andy Cuffe" > wrote in message ... > On 08 Dec 2004 19:23:31 -0500, Sam Goldwasser > > wrote: > > > >The sample I have drives both the magnetron high voltage and filament > >from the same transformer. I would think this is hard on the magnetron > >at moderate power where the filament isn't as hot as it should be but > >perhaps it's not a big issue. > > > > > The best microwave design I've seen is an Amana from the late 70. It > has a separate filament transformer, so it can modulate the HV at > something like 1 Hz while keeping the filament hot. This is fast > enough to stop things from exploding/boiling over while the magnetron > is on. It's the only microwave I've had where the low power levels > were actually useful. It also has to be easier on the magnetron. > Andy Cuffe > Those old Amanas were great, wouldn't mind having one now even, nice stainless cavity, metal control panel, really slick. |
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"Andy Cuffe" > wrote in message ... > On 08 Dec 2004 19:23:31 -0500, Sam Goldwasser > > wrote: > > > >The sample I have drives both the magnetron high voltage and filament > >from the same transformer. I would think this is hard on the magnetron > >at moderate power where the filament isn't as hot as it should be but > >perhaps it's not a big issue. > > > > > The best microwave design I've seen is an Amana from the late 70. It > has a separate filament transformer, so it can modulate the HV at > something like 1 Hz while keeping the filament hot. This is fast > enough to stop things from exploding/boiling over while the magnetron > is on. It's the only microwave I've had where the low power levels > were actually useful. It also has to be easier on the magnetron. > Andy Cuffe > Those old Amanas were great, wouldn't mind having one now even, nice stainless cavity, metal control panel, really slick. |
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In article <IUuud.17248$U47.1533@clgrps12>, "NSM" >
wrote: >http://www.antiquewireless.org/otb/60cycles.htm Typical US-centric--no mention of 50Hz. |
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In article <IUuud.17248$U47.1533@clgrps12>, "NSM" >
wrote: >http://www.antiquewireless.org/otb/60cycles.htm Typical US-centric--no mention of 50Hz. |
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"Lawrence DčOliveiro" > wrote in message ... > In article <IUuud.17248$U47.1533@clgrps12>, "NSM" > > wrote: > > >http://www.antiquewireless.org/otb/60cycles.htm > > Typical US-centric--no mention of 50Hz. Not just US, but all of North America, that's probably where it was written, hard to blame them. The story on 50Hz is pretty similar I'm sure. |
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"Lawrence DčOliveiro" > wrote in message ... > In article <IUuud.17248$U47.1533@clgrps12>, "NSM" > > wrote: > > >http://www.antiquewireless.org/otb/60cycles.htm > > Typical US-centric--no mention of 50Hz. Not just US, but all of North America, that's probably where it was written, hard to blame them. The story on 50Hz is pretty similar I'm sure. |
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Sure you have your facts right Bill?
I understand the iron losses increasing, but why does copper cable 'only use the outer quarter inch'? My understanding is that this phenomena kicks in at much higher frequencies - like above 50KHz. Another factor in choosing the frequencies may have been to do with audibility. I can imagine a (say) 800Hz transformer or motor making an intolerable racket compared to a 50Hz model. Regards Ron .. "Repeating Rifle" > wrote in message ... > in article , Lawrence DčOliveiro at > _zealand wrote on 12/10/04 12:24 PM: > > > I heard that Tesla wanted mains frequencies to be around 300-400Hz for > > this reason. I think the engineers who built the early power plants > > (Edison?) felt this was impractical because they couldn't build big AC > > generators that could spin that fast. > > > > Wonder how things would be different if the situation could be revisited > > today... > > Very briefly, the commercial power frequency selected is a tradeoff between > costs of equipment and size of equipent. Core losses, from the iron in > transformers, increase with frequency. For 60 Hz ac, only about the outer > quarter inch of copper in cables is used. As frequency is increased, less of > the copper conductor is used. In the end 60 Hz is used for most European > power while 60 Hz was selected for the USA. In aircraft, weight can be much > more of an economic factor then efficiency. Thus 400 Hz is popular in > aircraft. But realize that only about 0.1 inch thickness of copper is > useful. > > Bill > |
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Sure you have your facts right Bill?
I understand the iron losses increasing, but why does copper cable 'only use the outer quarter inch'? My understanding is that this phenomena kicks in at much higher frequencies - like above 50KHz. Another factor in choosing the frequencies may have been to do with audibility. I can imagine a (say) 800Hz transformer or motor making an intolerable racket compared to a 50Hz model. Regards Ron .. "Repeating Rifle" > wrote in message ... > in article , Lawrence DčOliveiro at > _zealand wrote on 12/10/04 12:24 PM: > > > I heard that Tesla wanted mains frequencies to be around 300-400Hz for > > this reason. I think the engineers who built the early power plants > > (Edison?) felt this was impractical because they couldn't build big AC > > generators that could spin that fast. > > > > Wonder how things would be different if the situation could be revisited > > today... > > Very briefly, the commercial power frequency selected is a tradeoff between > costs of equipment and size of equipent. Core losses, from the iron in > transformers, increase with frequency. For 60 Hz ac, only about the outer > quarter inch of copper in cables is used. As frequency is increased, less of > the copper conductor is used. In the end 60 Hz is used for most European > power while 60 Hz was selected for the USA. In aircraft, weight can be much > more of an economic factor then efficiency. Thus 400 Hz is popular in > aircraft. But realize that only about 0.1 inch thickness of copper is > useful. > > Bill > |
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On Sun, 12 Dec 2004 02:37:17 GMT Repeating Rifle
> wrote: >Most applications have wire smaller than 1/4" For example, #10 wire, by >eyeball, is about 1/10". And that is diameter. This skin effect is what >limits the effective size of the conductor. You're correct, at the consumer's end, but I believe the concern over losses was more for the power transmission lines. At 60 Hz, the skin depth is about 1 cm (~3/8") so this is already a factor with 4/0 cable. Inside your home it's irrelevant. I suspect that for long distance transmission lines the stranding is often a mix of plated steel on the inside for strength and copper on the outside for conductivity. The skin depth makes that a reasonable choice. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
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On Sun, 12 Dec 2004 02:37:17 GMT Repeating Rifle
> wrote: >Most applications have wire smaller than 1/4" For example, #10 wire, by >eyeball, is about 1/10". And that is diameter. This skin effect is what >limits the effective size of the conductor. You're correct, at the consumer's end, but I believe the concern over losses was more for the power transmission lines. At 60 Hz, the skin depth is about 1 cm (~3/8") so this is already a factor with 4/0 cable. Inside your home it's irrelevant. I suspect that for long distance transmission lines the stranding is often a mix of plated steel on the inside for strength and copper on the outside for conductivity. The skin depth makes that a reasonable choice. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
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On Sun, 12 Dec 2004 02:37:17 GMT Repeating Rifle
> wrote: >Most applications have wire smaller than 1/4" For example, #10 wire, by >eyeball, is about 1/10". And that is diameter. This skin effect is what >limits the effective size of the conductor. You're correct, at the consumer's end, but I believe the concern over losses was more for the power transmission lines. At 60 Hz, the skin depth is about 1 cm (~3/8") so this is already a factor with 4/0 cable. Inside your home it's irrelevant. I suspect that for long distance transmission lines the stranding is often a mix of plated steel on the inside for strength and copper on the outside for conductivity. The skin depth makes that a reasonable choice. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
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