# Why do jet generators produce a higher frequency power then household electricity? [duplicate]

I know in most homes your local transformer provides a 50Hz or 60Hz power source. So all your hairdryers, dishwashers etc. are built to consume 50Hz or 60Hz power at 110 volts or 220 volts, depending on where you live in the world. On the aircraft engine generators use a much higher frequency (400Hz). Why is this?

• See Adam Davis' answer - "A generator or transformer that can handle a given load is physically smaller and lighter at higher frequencies due to issues with core saturation at lower frequencies." – RedGrittyBrick May 11 '14 at 8:33
• The other question asks why AC instead of DC (as in cars). Here, the question is specifically about the frequency. – paul May 11 '14 at 8:44
• One answer contains the following: It's the same reason 400Hz is used rather than 50Hz or 60Hz - weight. A generator or transformer that can handle a given load is physically smaller and lighter at higher frequencies due to issues with core saturation at lower frequencies. A smaller, lighter core can be used for higher frequencies. That's a dupe – SSumner May 12 '14 at 15:02

This is a bit speculative, and if I am wrong, I will stand corrected.

Based on my little experience with power plant gas turbines, the frequency depends on the rpm of the turbine and the number of poles of the generator. A power plant turbine runs at 3000 rpm (for 50 Hz) or 3600 rpm (for 60 Hz), with two poles (this is the most reliable design, and works with turbines with rotors up to about 4 m diameter.

An aircraft APU is much smaller, and will run at higher for optimized power output. So, for the 400 Hz, you would have, for example, 12000 rpm and 4 poles (or 24000 rpm and 2 poles).

It already has been mentioned that transformers can be way smaller and lighter for higher frequencies, and it may also be that the higher freqencies of the harmonics cause less interference with other systems of the aircraft.

The speed of the generator is held constant, regardless of the engine's rpm, by the use of a Constant Speed Generator or Integrated Drive Generator.

• think your right and according to this site (400hertz.net/faqs.htm) 'This power limits the RPM of the fastest induction motor to a maximum of 3,600 RPM. The maximum speed of a 400HZ induction motor is 24,000 RPM, approximately seven times faster than is possible with a 60HZ motor. This higher speed and the use of higher quality wire and lamination steel make it possible to produce motors with 10 times the power for the same weight and same size as a 60HZ motor.' – esé May 12 '14 at 4:28
• This answer is plausible but wrong. The APU or engine generators could produce 50 Hz or 60 Hz quite easily if that were what was desired. There are good reasons why the higher frequency is what's desired, as referenced in the one answer to the (hardly a duplicate) question that's mentioned in the comments to the question, above. See also, this question. – Ralph J Mar 18 '17 at 18:10