Cable Ratings

Try some of these: cable sizing voltage drop derating factor PDF Download

Also, 67model gives a good explaination here:"Re: 400 HZ Aerospace Appllications" by 67model

thnks Lynlynch a very helpfull guide that was

SAK

Refer the standards IEC 60228,class 5 and VDE 0295. 400Hz cable construction is different than normal 50Hz or 60Hz cable. The cable manufactured with the consideration of skin effect. Please see some 400Hz cable data.

cable selection depends on Rated voltage, Dc conductor resistance,inductance,voltage drop,current rating, conductor temperature ,ambient temperature and maximumshort circuit current.

Advice:- Please contact any manyfacturer before starting your design.

Seconding the advice of the third reply; contact your wire/cable supplier. Most wire/cable companies have software models in their cable design which will calculate the parameters of interest and are very happy to aid in design.

Best regards,

Stef

1. Derating factor for a single isolated cylindrical conductor at 400 Hz can be judged from a 5% increase of resistance over DC resistance for an 0.8 cm diameter conductor. It will be less for smaller diameters.But it would be best to consult a cable manufacturer for tested ratings.
   
2. Inductance of a 2 wire circuit depends mostly on the spacing D between conductors as a ratio to conductor radius r (i.e. D/r). Inductance is 0.063 + 0.46 x log (D/r) microHenries per metre. For D/r = 4, it is about 0.33 microHenry/m. The "constant" 0.063 is actually for a 7 strand conductor and falls to 0.05 for 37 strands.
3. The inductive reactance for D/r = 4 comes out as about 1.8 mV/Amp/metre at 400 Hz. This means that for about 20 sqmm, the inductive reactance X is about twice the resistance R. At this ratio, the impedance is about 2.3 times the reactance - for bigger cables the resistance will hardly matter for volt drop, noting Z² = R² + X².
4. For 100 amp cable rating, 1.8 mV/A/m is 180 mV/m. 3.6V drop over 20m run - about 3% of 115V.
5. Hence over long runs, volts drop may be more important than rating reduction.
   
6. Considering 4. - on a long run, multiple cable pairs in parallel may be the only way to reduce volt drop. Ring circuits may be more effective than spurs for all.
7. I would check-up on the effect of wires in steel conduit and trunking. Even at 50 Hz wires in conduit see significant increase of S/C impedance compared to wires in non-metallic trays.
   

Thanx 67 for the reply will guide me appropriatly

Pardon me, SAK, but I goofed on item 3 of post#5. My ancient brain pulled out the volt drop per sq. mm for 1 metre length of copper - not the loop resistance. The other bits I got from text or tables. Reactance becomes twice resistance for 50 sq.mm, so the bit about 100 Amp cable was OK. One more thing - with so much inductance drop, you can get unbalance between phases unless you use the symmetrical trefoil arrangement for 3 ph single core cables.