Generating 50 HZ

How much you want ?

Or you want each generator to have variable output frequencies ?

By the way we have 0 Hz too

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Simply because they are agreed standards. They are in this area because they are convenient for the engine speeds for the internal combustion engines used for the pime mover of the generators.

50 and 60 Hz have become accepted. The benefits of standardization are obvious but it was not always so.

The mining town of Broken Hill, in Australia use 40Hz as recently as the 1970's. They have since been linked to the grid and now have standard 50Hz power.

I came across this because they needed a new dewatering pump, a 12 stage centrifugal.

Had they had 50Hz power the required pump would have been significantly smaller and cheaper, as would the required motor.

I have been told that Russia uses 60 Hz , 480V, getting the best of both worlds. Does anyone know if this is true?

There is no real difference in size and cost between 50/60Hz motors. Only few application will benefit from 20% more or less speed to save a gearbox but these special applications are evenly spread across the two frequencies.

Eg. A blower will give you higher pressure and lower flow on a 60Hz motor than on a 50Hz one. This might be useful or might not. If what you need is torque, the lower speed of a 50Hz motor will give you more for the same power and pole number. It all depends on what you need.

In general, the designs have been adapted to have the same level of performances in each continent. There isn't any superior frequency, only different trade off.

The higher the frequency, the less copper is required to convert the power in a transformer.Less losses also.Consider switch-mode power supplies, versus the old "brute force" transformer type.The switch mode type converts the line frequency(50 or 60 Hz) into DC.It uses this DC to charge a capacitor.The voltage of this capacitor is monitored and voltage is taken from the AC line when needed to keep it at a desired level. Power is taken from this regulated DC supply, and converted to a high-frequency(20 -50 Khz) which is applied to a very small transformer which provides various output voltages for rectification.The reason for the high frequency conversion is the reduced copper required for the same amount of power, and the higher efficiency of the system as a whole due to the higher frequency. As previously stated, a motor or transformer can be designed smaller for the same amount of power output,saving copper,weight, and heat,resistance and inductive losses by using higher frequency. Conversely,for transmitting very large currents over very long distances,DC is used.There are no inductive or self-heating losses, and frequency matching at each end is accomplished by inverters.This simplifies phase-matching between different systems of the power grid.

I do not know why 50 Hz is used. But I know that there is at least one advantage in using 60 Hz. In so many clocks and timers 60 Hz is used as the time base. In the middle of the night, generating companies run the generators faster or slower for a short period to compensate for the error.

That's an advantage of standardisation, not of 60Hz. Most of the rest of the world uses very similar clocks/timers designed for 50-Hz.

The choice of frequency was a trade-off - it would make little sense to changing it now.
For the record, 60Hz requires smaller motors and transformers than 50-Hz, and it also gave less visible flicker with direct-ballast fluorescent lamps. But the interaction with the human nerve system means that you are less likely to continue gripping the wire if you touch a 50-Hz "live", and 50-Hz can be run 20% further before resynchronisation is needed

I agree with # 7. My factory manufactures heaters in which we use a verity of step-down transformers, mainly 240 secondary, 350 VA. Currently we use 50/60 Hz transformers. My vendors suggest that if I agree to go with straight 60 Hz transformers, they can reduce the prize by a fair amount.

guest; i think its a metric thing! 20 milliseconds vs 16.666 milliseconds. perry

I'm not certain of the reason - I think it was purely parallel and independent developments by various private companies, and it just happened that 60-Hz won out in the US and 50-HZ in Europe. Perhaps it could just as easily have been 64-Hz...

(If metrication had been the reason, wouldn't the Brits have gone for 60-Hz?)

The use of 60 Hz for clocks is not unique. 50 Hz works equally well. Through my youth in the 50s & 60s the family mantle had an electric clock built by my Dad. It kept perfect time for the reason you have stated but it was a plain square box painted "wheelbarrow" green!

Modern clocks use a crystal, normally a 3.58 mhz one, because they are so cheap.They were once used in all US made tv sets for the chroma signal, so hundreds of millions of them have been made.The synchronization to line frequency is old technology, but it worked well for the time period, and true, it did not matter if it was 60 0r 50 hz, the clock was designed for that frequency.

Once upon a time, televisions used the 60 hz power line to synchronize the vertical scan of the set in the United States(NTSC standard).A vertical hold adjustment knob was provided to allow for local variations in frequency (difference between transmitting station and receiver).As counter and divider chips became cheaper, it was more beneficial to divide the horizontal scan rate (15750) by 525 to get the vertical scan frequency.The vertical adjustment knob was eliminated, and the picture never rolls because the horizontal scan frequency is part of the transmitted signal, always in sync. Now digital is making all of this technology obsolete as well. I feel like Fred Flintstone sometimes.

shoeshineboy; the crystal in watches & clocks are 32,xxx cycles, they are smaller then 3.58 xtals. Tulsa first project was water powered generators at Niagara falls, and ran at 25 cps or Hz for years, perry

A/C Technology used today was pioneered by Tesla, and he chose 60 cycles arbitrarily, because it was a common unit of measure for clocks,and degrees, minutes,seconds of latitude, longitude, etc. at the time. The higher the frequency, the smaller the transformer and motor required for the same amount of horsepower.This is one reason most airports use 400 Hz.Also, the Hz determines the maximum RPM for synchronous motors.The formula is: Hz.x120/ number of poles.For 60 Hz, this works out to 3600 RPM.For 400 Hz this works out to 24000 RPM. If all industry was standardized to 400 Hz, the transformer feeding your house would be very small.

but phase re-synchronisation would be required at about 1/7th of the present spacings - a complete nightmare.

Hi Shoeshine,

Why would airports use 400Hz? Their power generally comes from the main national grid and so surely will be 50 or 60Hz. Aeroplanes do use 400Hz, partly for the reason you stated of the lower weight but also because 24000 rpm is a convenient speed to run a turbine generator.

Chas

Ever work as electrician at an airport?Do you know of which you speak? Of course, other countries may be different than USA.

Hi Shoeshine,

I've only once done any electrical work in an airport and that was to service a standby generator. This was definitely 50Hz. But why should they want to go to 400Hz? The reasons to go to the higher freq have no advantages for the fixed installations of the airport. The ground support systems for the aircraft will be 400Hz which is the output from the mobile units supplying the planes on the apron. I don't know if the mobile walkways have a provision for 400Hz support.

regards

Chas

I will not be much bothered about synchronisation but think about the machine balancing required of the poor turbines and generators at the velocity corresp to 400Hz the balancing requirement may oughtweigh the weight advantages (esp when we go about making 500MW and above TG sets)

And add to that the inductive losses (power lines) as well as the the insulatore which will act significant capacitive at higher frequency.

More poles equals higher frequency for same rpm on alternators,inversely for motors.Not necessary to increase turbine speed to increase frequency.Higher frequency results in smaller conductors,less load on towers,lower cost of design, and open air conductors have no insulation around them.Current lead/lag can be easily compensated for by design.

we are talking of generating stations with air insulation at generating voltage of say 11KV for generators of 1000MW or more ?

guest; good answer more poles, alternators were use for radio transmissions years ago. i could show you a 400 Hz ballast the size of your finger, less iron smaller size. perry

"Current lead/lag can easily be compensated by design". Maybe (I'm not certain) this would be marginally easier at higher frequencies - but at high powers it is never "easy" and always costly.

But my real disagreement with this post is that I cannot see any reason why higher frequency would "result in smaller conductors, less load on towers". In fact, the reverse is almost certainly true when the current is large enough that conductor design has to take account of skin effect (as either litz-type conductor design or individual conductors with larger surface area would be needed, and either of these will result in increased wind resistance at best).

As similar constraints already apply in the windings of the generators, and given the relative costs of the different parts of the system, it would be unsurprising if this alone was sufficient cause to stay right where we are at the moment.

Power lines are designed as transmission lines - so there should be no inductive loss.

There is, however, an additional transmission reason for choosing a lower frequency - the skin effect would mean that the maximum strand diameter you could use would be 1/3 of present sizes - and I suspect that for this purpose some insulation (albeit very thin) would be needed between strands of the same phase .

If it were 0 Hz, you would have surely asked, why it is 70 Hz.

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CORRECTION:

If it were 70 Hz, you would have surely asked, why it is 70 Hz.

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its just that tesla 4 the first time experimented with 60 hz as frequency is like no. of times in a unit(like 60 sec in a minute)...so he adopted this metric system of units wen it came to europe and britain ..they did it at 50 hz acc. to their metric system of units. thats it