ivol
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I'm working on upcoming project where I need to delivery 3200 Amps / 8 VAC from Scott T transformer to my filament. What size of wire I should use?
Thanks
Thanks
Wire size for 3200 Amp
- Thread starter ivol
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How long are the wires going to be? At 8VAC the voltage drops can rapidly reach a high percentage, so code minimum wire size for the amps required may not be good enough.
It looks like you will have to use parallel wire sets.
Is this field wiring or part of a product assembly?
And just from curiosity, why a Scott-T? I would not think that filaments would require two phase.
Or are there two filament windings to be fed in quadrature for even heating across each cycle?
mobile
It looks like you will have to use parallel wire sets.
Is this field wiring or part of a product assembly?
And just from curiosity, why a Scott-T? I would not think that filaments would require two phase.
Or are there two filament windings to be fed in quadrature for even heating across each cycle?
mobile
Julius Right
Senior Member
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- Electrical Engineer Power Station Physical Design Retired
As GoldDigger already said :
it depends-usually- on some factors:
length of the cables or busbars
distance between parallel cables
material[copper or aluminum]
allowable voltage drop
allowable conductor temperature
ambient [air usually 40oC, Earth 20]
cable raceway[free air, exposed to sun, wind velocity, cable tray, buried and so on]
frequency[ 50, 60, 400 or else Hz]
For instance for 20 ft length 4% drop , copper busbar H/W=1.5 Tc=60oC one width clearance
in free air, Ta=40oC, no sun 2ft/sec wind a 1400 mm^2 [ 2800 MCM] cross section area is required.
it depends-usually- on some factors:
length of the cables or busbars
distance between parallel cables
material[copper or aluminum]
allowable voltage drop
allowable conductor temperature
ambient [air usually 40oC, Earth 20]
cable raceway[free air, exposed to sun, wind velocity, cable tray, buried and so on]
frequency[ 50, 60, 400 or else Hz]
For instance for 20 ft length 4% drop , copper busbar H/W=1.5 Tc=60oC one width clearance
in free air, Ta=40oC, no sun 2ft/sec wind a 1400 mm^2 [ 2800 MCM] cross section area is required.
kwired
Electron manager
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What kind of application uses such a high amperage but at very low volts - still leaving you with a fairly moderate overall KVA that could be handled much more economically at say 240 volts?
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The OP said it was for one or more filaments (heaters) possibly in klystrons or other high power vacuum tube devices.
That sort of application is best served by keeping the entire filament as close as possible to a uniform, constant, applied voltage. That means heavy wire at low voltage.
I once made filaments for the vaporized metal source for a vacuum pump for a space simulation chamber. I pounded titanium washers onto a ten inch long tungsten rod to carry about 1000A. The whole thing glowed red to white hot.
mobile
That sort of application is best served by keeping the entire filament as close as possible to a uniform, constant, applied voltage. That means heavy wire at low voltage.
I once made filaments for the vaporized metal source for a vacuum pump for a space simulation chamber. I pounded titanium washers onto a ten inch long tungsten rod to carry about 1000A. The whole thing glowed red to white hot.
mobile
3200 amps at 8 volts? Are you sure that's correct?
I don't know anything about scott transfomers, or whatever your application is, but say you start with 16 volts, you can have a maximum resistance of .0025 ohms to still have 8 volts left at your filament.
I don't know anything about scott transfomers, or whatever your application is, but say you start with 16 volts, you can have a maximum resistance of .0025 ohms to still have 8 volts left at your filament.
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The transformers are essentially wound with busbar to get that level of current.
The winding has to be large to safely carry the current regardless of the voltage, of course. But the voltage drop is indeed more of an issue when the nominal voltage is so low.
mobile
At that current I'd keep the distances short and use copper busbars.
kwired
Electron manager
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- NE Nebraska
Seems like the source impedance would cause problems at that current/voltage level before you even start to think about the conductors leaving it.
JFletcher
Senior Member
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- Williamsburg, VA
Scott T transformers are for supplying 2 phase power... what on Earth are you working on that would require 3200A @ 8VAC of 2 phase power? Looks like a vacuum tube heater, and something isnt right with your numbers. Regardless, I doubt this is an NEC question or installation.... 2016 code cycle.... yeah....
kwired
Electron manager
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- NE Nebraska
It is in the caculations/engineering forum and not the NEC forum. Still seems pretty strange to run such a low voltage at such a high current.
3200 amp @ 8 volts = 25.6 kVA. If it is two phase probably need double that to 51.2 kVA.
Put 51.2kVA on 480 volt three phase and you only draw 61.5 amps and spend a lot less on conductors. Has to be a very special reason to need to run at 8 volts.
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For the same reason you do not generally get 480V incandescent bulbs. There are mechanical constraints on heated filaments that make particular voltages more suitable for a given power level.
Also, if the filament forms a directly heated cathode you simply cannot have the two ends at widely different voltages compared to the "plate" voltage.
mobile
Also, if the filament forms a directly heated cathode you simply cannot have the two ends at widely different voltages compared to the "plate" voltage.
mobile
I did a few welding rectifiers. They were nominally 7V, 7,000A.
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As mentioned earlier, FWIW, two equal heaters in quadrature on two phase or a corner fed square on two phase produces a uniform total heat input over time. Three phase would take three heaters to achieve the same result.
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