Some countries don't regulate the voltage and don't regulate the frequency of their electricity.

In part of North America the electricity frequency used to be only 25Hz. The transformers and motors in appliances were enormous.

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Uncle $crooge

 

This I realize, but how do the power companys in advanced countrys keep this so accurate? What happens when you have more then one power plant or generator on a grid? If the frequency isn't synched perfectly, won't you end up with a goofy harmonic?

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If everything on the grid is not in perfect sync then there will be plenty of smoke.

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Uncle $crooge

 

The generators have to be synchronised before connecting to the grid. Once connected, the generators are effectively locked together, so the whole grid runs at the same speed.

The generators are synchronous, so they run at the speed of the grid, whatever torque is applied to them.

 

I've no idea how it's done now, but YEARS ago in the UK they used to have two clocks in the power station, one was an accurate standard clock, the other fed from the generated mains - during the course of the day, as load varied, it would run slightly fast, or slightly slow - but at midnight they would speed up (or slow down) the generators to make it read the correct time again.

This meant mains powered clocks had (and still do have) excellent long term accuracy, but may vary a second or two over a 24 hour period.

I've always wondered (and been amazed) that they can keep all the grid syncronised to each other - presumably it's cleverly designed to make it fairly automatic?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

There is a type of induction motor that can be wired up as a transformer. At equal frequencies on primary and secondary, it appears as a transformer. If one is slightly off the induction motor will slowly spin and allows for two different frequencied grids to be connected together. I think it's used somewhere between the Canadian and American electrical grids.

 

Hi Lefty,

I think the skin effect does not influence a 400Hz line very much if at all. I also don't know why 50/60Hz is used by electric suppliers. The german railroad however uses 16 1/3Hz for the electrically driven trains.

In the beginning of supply of electric power to households just DC was used. Since DC tends to fry organisms like human bodies it was changed to AC later. Never touch a high tension DC power line. You'll not be able to separate from the cable and BBQ'ed right away!

Regards

Hans

 

"Never touch a high tension DC power line. You'll not be able to separate from the cable and BBQ'ed right away! "

Good advice, but I think I will apply that same rule to high tension AC power lines also

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Measurement changes behavior

 

And from wikipedia:

"Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency."

Lefty

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Measurement changes behavior

 

just with a slight difference: Touching a high tension AC power line you'll be dead instantaneously. Touching a high tension DC power line you'll be electrolytically shrunk and need a small box only for the funeral.

 

Capacitive and Inductive losses don't exist as they are 90° out of phase with each other. There maybe increased I²R losses due to the out of phase currents however this is the same whatever frequency. The impedances are higher/lower due to the higher frequency but can be corrected with smaller inductors/capacitors.

Mike.

 

Mike: I didn't speak about losses (I^2R) as they don't deppend on frecuency.

I was speaking about voltage drop and leakage currents (in both cases 90º out of phase, so they don't cause extra losses)

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E Cerfoglio
Buenos Aires
Argentina

 

For very long runs sometimes even DC is used for transmission voltages.
In New Zealand between the North and South Island a 620 kV DC link is in used between Benmore and Haywards (Wellington).

400 Hz is used in the airforce and navy, main reason is weight and efficieny.

I worked in the airforce in The Netherlands and we used diesel gensets running at 1500 RPM with 32 pole alternators to get the required frequency.

When on the 50 Hz mains rotary converters were used running on 3Ø 380Volts 50 Hz converting it in 3Ø 416 Volts 400 Hz.

The physical size of the alternators wasn't that much bigger than the 50 Hz ones i recall of memory.

The American 60 Hz system is more efficient than the 50 Hz system which was pushed by AEG and the European SI system which prefers numbers 1,2 and 5. The 6 didn't fir in that series hence they settled on 50 Hz.

Idealy 230 Volts 60 Hz would be the better option than 110 Volts 60 Hz and 230 Volts 50 Hz IMO.

In the 50's railways used 16 2/3 Hz and 25 Hz (USA) and some countries still do. Germany and Switzerland use 15 kV 1Ø at 16 2/3 Hz.

Mainly to reduce sparking at the brushes at the traction motors at low frequency and have the advantage of AC with autotransfomers along the line and thinner OH catenary as opposed to the 1500 V and 3 kV systems in The Netherlands and Belgium. with many rectifier stations and heavy OH wiring.

__________________
There are more ways to get to Rome.

Electricity, Electric clocks, Meters and Trains are great.

Please don't sent me private messages, I will not answer them.
The questions asked can be discussed in the open forums.
http://www.youtube.com/user/RODALCO2007 some interesting electrical stuff to watch.

 

Nigel, I didn't read the second page of this topic, hence this reply.

Electric master clocks as you probably aware from of my other posts, i collect them and know a bit about them too.

The power station masterclock had a differential mechanism in it which was driven via a mains operated clock and a pendulum precision clock,
( now these days the pendulum clock is a precision quartz clock which may even get corrected occasionaly via a satelite time signal when the drift is out more than 1 second or so. )

If the difference was say more than one or a couple of seconds slowly the governor is adjusted by a minute amount. This has to be done slow otherwise the risk exists that one or more power station alternators grab all the load and trips on overload. Reactors are fitted in the lines to the step up 11 kV / 220 kV transformers to dampen excess currents, also the transmission lines will absorb minor frequency differences in extra losses.
A thing you want to avoid in a grid is hunting of alternators which can cause instability and stations to trip out on over or underfrequency. Time delays are also applied to the controlgear to minimise it going back and forth.

Alternators, when synchronised will keep in synch with each other. If the prime mover loses power the alternator will run as a motor and will remain locked in untill taken off line by the protection settings.

__________________
There are more ways to get to Rome.

Electricity, Electric clocks, Meters and Trains are great.

Please don't sent me private messages, I will not answer them.
The questions asked can be discussed in the open forums.
http://www.youtube.com/user/RODALCO2007 some interesting electrical stuff to watch.

 

http://www.med.govt.nz/templates/Mul...e____4335.aspx

Link explains some of the terminology used in power systems.

Hope it works

Cheers, Raymond

__________________
There are more ways to get to Rome.

Electricity, Electric clocks, Meters and Trains are great.

Please don't sent me private messages, I will not answer them.
The questions asked can be discussed in the open forums.
http://www.youtube.com/user/RODALCO2007 some interesting electrical stuff to watch.