# Relationship between frequency and power

I'm an electrical apprentice, just studying electrotechnology. I know this doesn't really have anything to do with my trade and that I don't need to understand, but I'm curious as to how a change in frequency will affect power, or if it affects power at all, or if I'm on the wrong track completely. What does a change in frequency do to current, etc.?

To keep it very simple, if you have a 1000 watt heater intended to operate on 120 V 60 Hz power, it will produce the same heat at 50 Hz or 400 Hz, provided the voltage remains at 120 V. When you get into motors, transformers, and other non-resistive loads, the power may vary with frequency.

It can certainly affect power. Reactive elements will take more or less (reactive) power with changes in frequency. Many lossy components will have losses that increase with frequency (hysteresis losses, skin and proximity effects). It really depends on the load, and the frequency range you are considering. If you have specific examples we can comment further.

• Okay, what you've told me so far makes sense. I first thought about it when considering America runs on 110 or 115v at 60hz but in Australia we are able to run on 240V at 50hz, do they both supply the same sort of output? Like would an appliance from Australia run on 110v at 60hz? @John D – Daniel Smith May 1 '14 at 4:04
• @user41167 The answer to your question is both yes and no. What generally happens in appliances is the following: They receive mains voltage, and then they convert mains voltage to the voltage+frequency that the appliance runs on. This final voltage+frequency is dependent on the appliance and can change (anything from 5V DC(0Hz) for a USB charger, up to some kV and MHz for a microwave oven). The difference between an appliance that would work in US vs Australia would be the converter circuit. With that said, some appliances have a circuit that can convert from various Mains power sources. – Miron V May 1 '14 at 4:39
• @EEIngenuity has it right. Many devices these days are designed for "universal input" meaning that they can operate from something like 85-264 VAC and 50-60Hz. (So they can be sold all over the world without changes.) There are still lots of exceptions that will only run on one nominal voltage. (Hair dryers, conventional light bulbs. lots of white goods appliances.) The issue is mostly the voltage, not the frequency. There's little difference between 50 and 60 Hz as far as typical loads are concerned. – John D May 1 '14 at 4:44
• @Eeingunuity Oh, that makes sense! So what could you expect to see if your mains frequency were to fluctuate significantly? – Daniel Smith May 1 '14 at 4:49
• In the "old days" you could not interchange much. You could use an Australian electric heater in the US and get half the heat. A US heater would burn up on Australian power (P=IV and I=V/R. R of the heater doesn't change). Many US wall clocks will run slow in Australia. They are synced to the very accurate 60Hz of the power system. Today nearly all electronics use "switching" power supplies and take a very wide input. They have become very efficient and small. Most things with large motors or lots of power will still be specialized. – C. Towne Springer May 1 '14 at 4:51

In terms of power frequency, the core excitation current reduces for increasing f so turns are adjusted to yield capacity whatever core steel is chosen, typically 1.5T to 2T. Slightly less core mass in kW/kg with rising f for power transmission.

In terms of eddy current losses , they increase with f for same power density slightly.

Partial Discharge seems to be more affected by dv/dt excitation which is derived from V and f and insulation quality and contamination from voids or particles in solids and liquids.

For long haul DC is best.

There is no advantage to use 50 or 60Hz power systems in general but specific components may have preference.

But Aircraft prefer much higher f, for lower mass generators.

• Oh wow, thanks! I'm not too sure about what my question was, im amazed at how much detail everyone has gone into! I'll take some time to have a look and try to understand what everyone is saying and see if it helps my understanding, thanks everyone! – Daniel Smith May 1 '14 at 6:25
• "There is no advantage to use 50 or 60Hz power systems ..." 60 Hz will also require less mass as in your aircraft example and so they have to be de-rated for 50 Hz operation. 50 Hz has less losses in transmission (because it's closer to DC as in your answer). Overall, the benefits and disadvantages of 50 - 60 Hz relative to each other probably do balance out. – Transistor Jul 28 '18 at 8:24