Power Frequency

Personal preference that became a standard. One is not better than the other and both are well suited to their purpose.

history reason？

History is rarely reasonable.

It's based on a reasonable rotation speed for a large generator when the early ones were built. Once they were in use it became a standard.

Like most standards it is to a great extent arbitrary and based on simple convenience... look at the yard or meter... basically a stride.

Nature is no respecter of standards, it does it's own thing and we make ours standards to suit!

Del

only np/60? 50 and 60，which is better?

Neither is better, they're just different. Are apples better than oranges?

Well, yeah...

there is no "better" it's just arbitrary....

But obviously for equipment built to operate on 50hz... the 50 is "better"

Do try and pay attention

Del

This Wikipedia entry <click here> will throw some more light on the subject.

A helicopter mechanic might say that 400Hz is better.

The helicopter engineer will like 400Hz. The mechanic, probably won't. Have you ever been zapped by 400Hz AC? It feels like a wasp sting! The only good part is that it doesn't swell and leave you with a welt.

Not! if potential is aT 440Vac, 400HZ, taste even better

It's the designer who'll appreciate it most (maybe that's the kind of engineer you meant).

Smaller (and therefore lighter) motors and generators.

What will happen to your transformer if frequency is lower than 50Hz, say 5Hz?

The inefficient parasitic losses will change. Some will get better and some will get worse. For the most part these loss changes will compensate each other. The difference between 50 and 60 HZ is only a 20% change. The major power loss differences will actually happen in the downstream motors that will often spin at a different speed. In a transformer the saturation point in the core will be the major change. Since most transformers rarely operate near saturation (except during a turn ON surge or a fault condition) this is not a big problem. In contrast many motors are designed to work close to or in core saturation.

Or 16-2/3%; it depends upon where you start!

It was explained in USN AE school that increasing the frequency drops the dielectric constant allowing less creepage distance at higher altitudes.

It also prevents use of aircraft parts on 60Hz.

Correct me if I'm wrong. What I understand about Hertz is the faster the generator rotates the higher the Hz. Aircraft use 400 Hz because their on board generators spin at a high RPM being connected to the jet engine. Household electricity runs at 50 or 60 Hz as you know. For the generators to be large enough to power a city and spin at Aircraft RPM / Hz is deadly! Now back to the 50 / 60 debate. Which is better? What is the application? For every situation, there can be multiple solutions? Which is better?

My answer:

What performance are you looking for?

Higher torque?

Less noise?

What electrical supply do you have where you live? 50 Hz or 60 Hz?

The one my electrical company supplies is the better of the two in my opinion!

Well at this modern age, a 120Hz is easy to generate if intended.

Just a simple correction here. You are forgetting about the number of poles a generator has. A 60 Hz generator does not have to spin at 3600 RPM. This will change only in integer multiples. Deviations around the desired frequency will be due to changes in dynamo spin rate.

Seeing as the OP had difficulty expressing his question, I over simplified my answer.

Thank you for the clarification.

One of the reasons I participate in this forum is that as I read and reply, I learn more and more about the subjects that interest me.

Nope. 400 Hz equipment on board A/C came along way before jet engines were in use at all (as in the beginning of WWII), so it really has to do with the weight conservation of electrical equipment needed in flight.

Dear sir:

Thank you all!

It seems that my son understand!

My son and I both learn a lot from this!

but, if we can choose or determined the power frequency today,which will we choose,50，60，70，or100?

Ooops!!! it all depends to whats the frequency of your local power provider.

Do not attempt to buy 50Hz gadgets and use it at 60Hz supply, its economic life will be shortened a bit.

Using 60Hz gadget and use it on a 50Hz supply might work.

For assurance, choose gadget which has mark on the adaptor 50/60Hz will be best no matter where you go, you can plug it with no problem.

Not so kulas, many items rated for 60Hz get very warm when run at 50Hz as the reactance is lower and they draw more current, especially true of transformers

Imagine yourself back at the start of electrical generation. You don't really have all the information/technology that we have today, so,, you will just pick one, of course using what you know and have learned, and go from there. Like a lot of things, trial and error. Learn from your mistakes.

One advantage that 50Hz has over 60 Hz is in lower transmission losses.

A long AC transmission line has very large capacitances which build up, collapse and change direction in concert with the rise and fall of the sine wave voltage (100 polarity changes per second for 50Hz and 120 per second for 60Hz supplies). These capacitances (conductor to conductor and conductor to ground) cause line losses due to capacitive reactance, apply irrespective of the loading on the line and become greater with underground cables due to their closer proximity to each other, and also with larger cable bundles. 50Hz has roughly 17% less changes per second than does 60Hz and so results in lower capacitive/dielectric losses.

Another power line loss is called skin effect where the AC frequency causes an inductive reactance that limits current flow essentially to the outer annulus of the conductor (and the reason that many high voltage AC transmission lines having either a hollow or steel core have essentially similar impedance characteristics to full Al cables). This skin effect is greater (thinner skin depth for same CSA cable) with a higher frequency transmission, resulting in roughly 9% higher power losses for the 60Hz frequency transmission.

Taken together, these reactive impedances can be three times the actual line resistance and can cause very large line losses and are one of the main reasons that many new large power transmission systems are now using high voltage direct current.