Why 50/60 Hz?

Yes, and that only serves to verify my original answer, of yes and no, the speed that the prime mover spins the alternator all depends on the type and construction of the alternator itself..

----- Actually it is the other way around- the prime mover's characteristics determine the alternator's construction.

For a hydro plant, for example, the head is a critical factor in determining the turbine type and speed. The alternator is designed for a synchronous speed as close to the optimal turbine speed as possible.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

On Thu, 15 Jan 2004 00:07:37 GMT, Chris Gave us:

Given your reason why 1000Hz isn't used, one cannot be too sure.

Given your ignorance and lack of understanding on how fast an alternator is driven at....

What is amazing to me is that nobody here is aware of the fact that 50 cycles WAS at one time popular in the US.

When the Hoover Dam was built it provided 50 Hz power to southern California, which explains why many old electrical appliances were rated for

50/60 cycles long before exports became an issue. I don't recall the date, but at a point Hoover was refitted for 60 Hz, and little by little the 50 Hz system vanished.

The first commercial AC system was 133 Hz, the first long-distance power transmission was 25 Hz. Southern Ontario, Canada, was exclusively 25 Hz until 1957, when there was a total and complete conversion. If you poke around in Toronto you will find 25 cycle color television sets, radios, clocks, etc. Across the river in Buffalo there is still a tiny 25 Hz utility system, but its discontinuance has been scheduled for 2007.

The existing 25 Hz generating capacity is all converted to 60 Hz with static or rotary frequency changers.

60 Hz is a good compromise, but no better or worse than 50

See Mark Kinsler, "The 1938 Los Angeles Clock Changeover Project," IEEE Power Engineering Review, June 1997

?s falke

One thing that I could never understand was why single phase at 16 2/3 Hz was mooted as being suitable for traction in electric trains?

To the uninitiated (I am not a power engineer) it would seem that for a significant time there would be insufficient voltage to ensure smooth rotation of a motor under load.

(ISTR that at a recent IEE weekend, the history of the Bath scheme was given, where distribution to individual houses was at some kV at 400 Hz, each house having its own transformer)

Oh, that's easy.

In the pre-electronic era, a predominant means of converting AC to DC and vice versa was a device called a synchronous converter. This is a device that has only one rotating winding, but this winding simultaneously appears to be both the armature of an AC machine through one set of brushes, and appears to be a DC machine through another set of brushes. What is great about converters is that a significant amount of power goes straight through the winding without any mechanical intermediary. for example, a converter that is converting 100kW may be transmitting only 40 kW mechanically. This makes converters smaller and lighter than MG sets. Railroad practice was to use AC on the catenary, and use an on-board synchronous converter to generate DC for the motors. The low frequencies are preferred because they simplify some of the commutation problems associated with synchronous converters. That was also a primary consideration in the choice of 25 Hz for early industrial power transmission. The development of thyratrons and solid-state devices changes the picture, but the established standards remain.

On Sun, 18 Jan 2004 16:41:28 GMT, Chris Gave us:

Are you telling us that the majority of them are not 3600 RPM?

That is aside from the fact that higher frequencies can be obtained with slower spindle speeds. It's all about construction and drive source capacity.

DimBulb, read the thread. You've been outed as a know-nothing (again).

Indeed, read the thread Dimmie!

On Sun, 18 Jan 2004 20:01:58 -0500, Keith R. Williams Gave us:

Fuck off, KeithTard.

--------- For 3 phase motors, there will be no torque fluctuations at any frequency. However, rotary converters were once used and presently solid state electronics are used to convert to DC (16 2/3 is alive and well) The choice was a mix of economic and engineering factors.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

SO: when did 60 Hz start to take over?

EMWTK

My, my. Such eloquence from the DimBulb.

Traction motors run on DC - not AC (except really new trains now in use in Europe, they are AC/DC/AC VFD driven). Power generated for electric trains is generated and transmitted as AC for distribution efficiency (transformers). Substations are located along the rail system that convert the AC to DC for 3rd rail systems. In the NYC area, these substations used to use rotary converters to convert the AC to DC. It was these machines that benefited from the use of low frequency A/C source. These machines have been replaced 1st by mercury rectifiers and then by solid state equipment. Traction motors, however, are DC because of the ease of speed control and their torque curves. Nowadays, AC traction motors are being used in the newer trains. The DC rail power is converted to variable frequency AC by solid state VFD inverters on board the train. Some Cantenary systems deliver AC to the trains and the DC conversion takes place on board. These days much of the old electric railway power stations and transmission facilities have been converted to 60Hz now that rotary converters are no longer used.

From what I found while googling, there is still quite a bit of power generated on the Canadian side at 25 Hz. (total maybe 400-500 MW). The 25 Hz power on the US side is apparently imported from Canada (the US

25 Hz plants all either closed or collapsed into the river). I found some article on upgrading a 25 Hz 69kV feed. (who uses it and why?) Was there a massive 25-60 Hz upgrade in the Buffalo area similar to the 1957 Ontario upgrade? (Was that upgrade done area by area, and were there two sets of power lines on every street at the time of the switchover?)

The 25 Hz system in the Buffalo area was never systematically upgraded. 60 Hz was introduced very early, and the two simply coexisted through most of the 20th century. What kept 25 Hz going in the area for many years was the huge industrial base that made it and used it. Bethlehem Steel, Republic Steel, International Paper, Allied Chemical and many, many others were originally connected to 25 Hz, generated their own 25 Hz and never had a reason to change. There were movie theatres and hotels that had 25 Hz. With the decline of the area in the 1960s the big customers (and their revenue) disappeared. The 25 cycle customer base simply evaporated. There was never very much residential 25 Hz in the area, but there were a few patches in the Fillmore district. Downtown Buffalo was serviced primarily by 25 Hz and DC, until 1938 when the DC was discontinued. Most of the DC customers converted to 60 rather than 25, although 25 was available as a new service until, IIRC, 1968!

I have lost track of the system, but the last I knew there were a few c>

Modern computer power supplies aren't as good as older computer power supplies. My 10 yr old computer doesn't miss a beat when the mains power flickers. My 6 month old computer reboots, losing whatever I'm working on. Power supply designers seem to cut costs by putting in smaller capacitors in the power supplies.

Sig: You know, a lot of things, in this world, they make no sense. But now Im here, everthing make no sense.

A "universal" motor is a commutator machine that will run on either AC or DC. 16 2/3 Hz is a low enough frequency that quite large commutator machines can be made, and excited with ac, with acceptable efficiency and good commutation. Traction motors for trains were commutatot-type motors and so benefitted from the low frequency.

I don't think there was ever a 25 Hz colour TV - we didn't get colour broadcasting till the middle 1960's. My Mum recalls living in Sudbury Ontario and having all the clocks and record players swapped out for 60 Hz appliances. I do recall seeing old tube table radios marked for dc and 25-60Hz.

However, I have *operated* a colour TV on frequecies as low as 16 Hz - for a particular project I was using a small variable-frequency drive to run a TV recieveer in a dc-powered overhead crane cab. Of course when I had everything hooked up on the bench I had to find out "how low can you go" - the TV was working reasonably well even at very low voltage and frequency.

Bill

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