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#176693 - 04/09/08 03:12 PM High fequency power and electrical conductors  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,327
Alaska
I am just a magnet for oddities in the trade. I was just handed a project that will carry 240 volts at 3500 Hertz. Has any one had any experience with HF power? Is there special wiring that is needed? and additional matters to contend with as far as voltage drop? Interference from other circuitry like 60 hz? I am kind of tide of at the moment to research it. Any input would sure help. Thanx up front.


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#176699 - 04/09/08 05:30 PM Re: High fequency power and electrical conductors [Re: sparkyinak]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
How much current and how far? What is the load? Is it mostly resistive or is it reactive? My initial guess is regular THHN would be fine unless there is strict requirements as far as losses are concern. My only significant concern would be the insulation voltage rating if the load was reactive and the VSWR (Voltage Standing Wave Ratio)due to mismatched impedances was excessive.

Obviously circuit breakers and transformers are going to be outside their approval rating operating conditions.

Larry C


#176701 - 04/09/08 06:02 PM Re: High fequency power and electrical conductors [Re: LarryC]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,327
Alaska
240 Volts 5 amps 3500 feet 1500 Hz. Micro Hydro powering a charge controller. no info in the charge controller or micro hydro yet. That Is why I posted the question and for future reference.

Last edited by sparkyinak; 04/09/08 06:03 PM.

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#176724 - 04/10/08 12:20 AM Re: High fequency power and electrical conductors [Re: sparkyinak]  
winnie  Offline
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Joined: Sep 2003
Posts: 649
boston, ma
1) 'Skin Effect'. When AC current flows in a conductor, it tends to concentrate at the surface of the conductor. The amount of concentration depends upon frequency, and can be described in terms of the 'skin depth'. Skin depth is shallower at higher frequency, and for 3500 Hz, the skin depth is about 1mm. Wire resistance will be higher than you expect. You may need to parallel conductors to avoid excessive skin effect.

2) Transmission line effects. All cables have capacitance. All cables have inductance. The effects of capacitance and inductance become more noticeable at higher frequencies and longer lengths. I don't know if this is a significant issue for your application.

3) Ignoring the above, at 5A and 240V and 3500 feet, you will need 4ga copper in order to keep losses below 5%, by just 'ordinary' voltage drop calculations. $5K in wire to move 1KW; payback won't be quick. Can the alternator be wound for 480V?

-Jon


#176725 - 04/10/08 12:34 AM Re: High fequency power and electrical conductors [Re: winnie]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,327
Alaska
At the current time you know what I know. I will get a hold the guy tomorrow. His info didn't quite jive with me so I will find out what he is trying to do. Thanx


"Live Awesome!" - Kevin Carosa

#176730 - 04/10/08 07:06 AM Re: High fequency power and electrical conductors [Re: sparkyinak]  
SteveFehr  Offline
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Joined: Mar 2005
Posts: 1,209
Chesapeake, VA
I've worked somewhat with HF and other transmission lines, but never worked in the ULF range like you're in. You're probably going to need to use coaxial cable to transmit that unless high losses are acceptable- inductive losses with standard electrical cable are just going to kill you, even at a frequency this low. The coax shields you from EMI, too- shields everyone else from you, too. You can find tables from the manufacturers as to what the losses are for what cabling at what frequency range, and go from there.

You'll need to look at impedance-matching, too. The equipment should spec out an impedance and type of cable, and if it doesn't, the manufacturer will know.

This isn't 60Hz, so NEC won't necessarily apply.


#176850 - 04/14/08 05:45 PM Re: High fequency power and electrical conductors [Re: SteveFehr]  
Jonno  Offline
Member
Joined: May 2006
Posts: 20
This sounds like it will be feeding a rectifier-inverted setup to either connect to the grid or supply your loads. I would suggest pushing the engineers to install the rectifier at the generator terminals. Now you are dealing with 5 A DC, #14, would then be overkill.


#178683 - 06/09/08 08:49 AM Re: High fequency power and electrical conductors [Re: sparkyinak]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
What happened to the job? How did it turn out?

Larry C



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