400HZ Circuits

[faresos]

Hello Everyone:

I'm working on project (Avionics) that will involve to provide 120V, 20A, single & 3-Phase circuits @ 400HZ. My questions:
1. Can we use the same wire type that is used for 60HZ circuits or different type is needed?
2. My understanding the voltage drop will be an issue for higher frequencies, is there any derating factor can be used to determine the voltage drop for the 400HZ circuits?


Thanks,

 

[jumper]

I do not know anything about 400 Hz circuits, but I did find a few threads on the topic.

http://forums.mikeholt.com/showthread.php?t=153152

http://forums.mikeholt.com/showthread.php?t=91570

 

[Ingenieur]

one difference will be the Z of the conductor
Z = sqrt(X^2 + R^2)
R will be the same
X should increase by 400/60 (X = 2 Pi F H)
the wire should be the same since the voltage/insulation is the same

 

[winnie]

For small wires there is essentially no difference wiring 60Hz vs 400Hz. The 'skin effect' is more significant at 400Hz. Skin effect is seen in conductors carrying AC current where the current only flows in a 'shell' on the outside of the wire, reducing its effective cross section. The 'skin thickness' gets smaller as frequency goes up, which means that conductors at 400Hz have higher resistance than the same conductors at 60Hz.

Since skin depth is a fixed dimension for a given frequency and conductor material, with smaller conductors the effect is less.

For 12 AWG wire the difference in resistance is less than 1%. For 250 Kcmil wire the difference in resistance is some 25%. So for 20A circuits you don't really need to worry about skin effect.

You also need to consider inductive voltage drop, which increases as frequency increases. You should strongly consider using a non-magnetic wiring method, eg aluminum conduit.

You also need to consider that your circuit breaker ratings will change with frequency.

-Jon

 

[junkhound]

Hello Everyone:

I'm working on project (Avionics) that will involve to provide 120V, 20A, single & 3-Phase circuits @ 400HZ. My questions:
1. Can we use the same wire type that is used for 60HZ circuits or different type is needed?
2. My understanding the voltage drop will be an issue for higher frequencies, is there any derating factor can be used to determine the voltage drop for the 400HZ circuits?


Thanks,

Most aircraft 400Hz now have very stringent harmonic. PF, and other power quality specifications. NEC is not used. Newer aircraft also have variable frequency, such as 360 to 800 Hz, and also +/- 270 Vdc.
I have never seen THHN or similar on commercial aircraft, wire types are typically higher temperature.

If interested, search for typical aircraft wire specs, such as BMS13-60 or BMS13-78 which will give you a good idea of the wire types. There are various MS specification for aerospace wire also.
Totally different world than NEC.
PS: your avionics project (unless just DIY??) WILL have a specification sheet that defines the minimum temperature ratings (or even the required wire specification).

 

[junkhound]

PPS: OP used the word "avionics' which to me implies flight hardware (e.g something that goes ON an airplane)
If your use of the term 'avionics' just means a small ground test station or similar ground installation, then NEC would apply to portions of the setup.