50Hz versus 60Hz and power generation needed question

# Thread: 50Hz versus 60Hz and power generation needed question

1. ## 50Hz versus 60Hz and power generation needed question

From another forum -

Hence, just like 50 Hz to 60 Hz motors, in spite of the huge cost savings of 50 Hz motors (for the non-technical, it means that power generators run 10% slower, which means 10% less fuel used. Roughly

First off, I would think 20% difference, not 10%... and I suspect there would be no generator fuel cost savings but how best to articulate why ?

2. Plastic
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The question is why there should be fuel savings? The only argument I can think of will be: lower rpm therefore less "cylinder cycles" per minute therefore less fuel used.
But since one cycle takes more time you need higher torque to produce the same power.
50Hz generator may be more efficient (for example due to hysteresis/eddy current loses) but with out more specific argument cited statement is "not even wrong"
( Not even wrong - Wikipedia )

Wysłane z mojego SM-N950F przy użyciu Tapatalka

3. The output of a motor is energy per unit time, also known as power. Power is the product of speed (in this case RPM) and torque.

If you power a machine with a 60 Hz motor attached to a 60 Hz power source or you power the same machine with a 50 Hz motor attached to a 50 Hz power source, the machine will use the same amount of electrical power if it is doing the same work per unit time. Typically the 50 Hz motor will be turning at 5/6 the speed of the 60 Hz motor. It will then be connected to the machine with pulley which is 6/5 = 1.2 times the diameter of the pulley used with the 60 Hz motor. Turning this larger pulley requires 6/5=1.2 times the torque.

So: the product of the motor RPM and torque is the same for both motors, because both do the same work per unit time, and both use the same power. In the example I have given, starting immediately downstream of the motor pulley, both the 50-Hz powered machine and the 60-Hz powered machine "see" the same thing, namely a belt moving at the same speed (feet per minute) transmitting the same amount of (mechanical) power per unit time.

=======================

Unrelated side notes:

The reason that Europe uses lower line frequency than the US is historical, not saving energy. It has to do with competition between the Edison conglomerate / General Electric in the USA and Siemens / AEG in Europe.

The European use of a higher voltage (typically 230V) for household wiring compared with 120V for the USA does save some money because thinner copper wiring can be used for power distribution in houses (downstream of distribution transformers). On the other hand the 50 Hz transformers are larger and require more metal inside than their 60 Hz brethren, just as for the motors. The most efficient thing to reduce the cost of materials would have been 230V at 60 Hz for household wiring.

Final comment: a 50 Hz motor which produces a certain output power will on the average be slightly larger and use more materials than a 60 Hz motor which produces the same output power, for the same reason that 50 Hz transformers are larger than 60 Hz ones.

4. Aluminum
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I doubt it's worth your time getting too deep into a discussion with somebody that thinks 50 is 10% less than 60 (for the non-technical 60 is 20% more than 50 but 50 is 16.67% less than 60).
Last edited by tonymor; 05-24-2019 at 08:49 AM. Reason: Addition

5. Wait -- there are other forums on the internet?

6. Originally Posted by tonymor
I doubt it's worth your time getting too deep into a discussion...
Normally I would ignore this kind of sniping remark. But Milacron is the founder/owner of this message board. He's a very smart guy, perfectly capable of understanding and appreciating my reply, and both he and the boards have contributed a huge amount of useful information over many years. In fact he is doing that here, because he has moved a question posted in another less appropriate forum to this forum where a competent reply will follow quickly.

So you ought to cut him some slack rather than drawing attention to a trivial algebra mistake .

7. ballen has given a good explanation.

There are some energy savings that are easily visible, from two sources. They are not large, but can be significant in a large system.

1) distribution losses, not because of 50 Hz, but because of higher voltage. The current is lower, and the power lost in the wiring will be lower, even using wire of half the "size" to go with the halving of current.

2) Windage losses in motors and generators, because of the lower rpm.

8. Originally Posted by JST
There are some energy savings that are easily visible, from two sources. They are not large, but can be significant in a large system.

1) distribution losses, not because of 50 Hz, but because of higher voltage. The current is lower, and the power lost in the wiring will be lower, even using wire of half the "size" to go with the halving of current.

2) Windage losses in motors and generators, because of the lower rpm.
Regarding point (1): in practice a shop in the USA running at 60 Hz and one in Europe running at 50 Hz will have similar distribution losses, because the USA shop will have heavier gauge copper distribution wiring and thus lower resistance. So the I^2 R resistive losses will be similar. Note that this requires wire with twice the cross-sectional area in the US, so a diameter that is larger by a factor of the square root of two, roughly 1.4 .

Regarding point (2): at least for modern motors I think the main losses in motors are not in the wiring but in the eddy currents and hysteresis losses in the magnetic core materials. Thanks to modern material and better design tools, these days those losses can be quite small. From what I can tell, modern 50 Hz 3-phase motors have similar efficiency to a modern 60 Hz 3-phase motors. Because energy efficiency is important nowadays, motor nameplates often list this efficiency explicitly, so it's easy to compare.

Note that my experience is with small HP 3-phase motors but I think it's probably also true for 2-phase ones and for much larger ones.

9. Hot Rolled
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Frequency, voltage, current, power factor all come into play on the electrical side.
And then you can also start looking at the number of poles in a motor/generator when looking at speed/frequency.
For the larger engine-generator sets, 60Hz will be 720 rpm, 50 Hz will be 750 rpm from the same engine. Or 514rpm for 60Hz and 500rpm for 50Hz. For each case the speeds are just a few percent different, power and efficiency are basically the same from one speed to the other. Torque and speed balance to keep the power the same mechanically. Electrically you just need current and voltage for power - frequency doesn't come into play, theoretically. In the real world, you do need the frequency/speed to be something usable, and motor/generator losses are mainly driven by current.

10. Cast Iron
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I can only imagine the energy that could be saved were we to convert to 1hz or 0.5hz

11. Diamond
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Originally Posted by Milacron
From another forum -

Hence, just like 50 Hz to 60 Hz motors, in spite of the huge cost savings of 50 Hz motors (for the non-technical, it means that power generators run 10% slower, which means 10% less fuel used. Roughly

First off, I would think 20% difference, not 10%... and I suspect there would be no generator fuel cost savings but how best to articulate why ?

Electrical losses in any reasonable power transmission system will be a percent or so at most.

This means around 99 percent of the fuel used is to deliver real power to the loads on the system. This
cannot be changed because physics is a harsh mistress. Any purported fuel savings based on 50 vs 60
cycle systems (which WAS the original question) will be realized inside of that one or two percent of
electrical losses.

TLDR: the assertion is nonsense.

12. TLDR: Agree on the nonsensical nature of the original assertion.

Energy = work across time.
At 5/6 motor speed, less total revolutions means less work is performed in the same amount of time.
So to perform the same amount of work, the motor must run longer.
The only possible change in net energy consumed might be that the fixed losses in the motor may actually INCREASE at a slower speed because the motor must operate 17% longer to do the same amount of work.

13. Aluminum
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So whether a 50 or 60 hertz motor is more efficient really depends on the design. For sake of discussion, we should assume that the motors will have the same efficiency.

The generator running at 3000 rpm (50 hz) versus running 3600 rpm (60 hertz) should be just a little bit more efficient because of lower mechanical friction losses. This is not a large number.

The power output of the generator is based on how much fuel is used (fuel intake is based on actual power output minus engine and generator losses). The generator is a torque matching device. As more power is required by the load, the generator will start slowing down and by closed loop control (governor), the governor will add more fuel to the generator until the speed is again satisfied. So basically the same amount of fuel is used for the same load regardless if its running 50 or 60 hertz. There will be a little difference one way or another, but not much.

14. "Windage" in english is not "winding"...... The "windage" losses means loss due to the energy used stirring up the air. That is related to square or cube of speed, (do not recall which). So a small reduction can mean a larger energy saving at lower RPM. But this is not a large loss for most equipment.

The savings in distribution at higher voltage and lower current are significant, but are nothing to do with frequency aside from 50 Hz being associated with 230 vs120 V utilization voltage for residences and offices...

But they do depend on wire size, which is an economic decision. Just doubling current (same power at half voltage) increases losses 4x. Therefore the wire resistance may be 4x larger at higher voltage with no change of losses. Choosing a larger wire size can reduce the losses, and still use a smaller mass of conductor.

15. Titanium
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Most generators are either 2 pole (high speed) or 4 pole (low speed). There are other alternator pole configurations of course, but these are usually reserved for high power commercial power uses. Low power portable generators are typically 2 pole. These run at 3000 RPM for 50 Hz and 3600 RPM for 60 Hz. Low speed generators run at 1500 RPM and 1800 RPM respectively. Fuel consumption is usually stated as pounds of fuel consumed per horsepower hour. It is important to note that engine efficiency is NOT the same across an engine's usable speed range. So, depending on the engine and its specific design, the actual engine efficiency can be significantly different at these engine speeds. One cannot say that an engine is more or less efficient at either the 50 Hz or 60 Hz engine speed. It really depends of the engine and the efficiency difference can be significant.........much more than any electrical losses.

16. Stainless
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From what I have read about Tesla and Westinghouse was that Westinghouse's Engineers were attempting to get transformers efficient. AC power was well known but not used. DC was still the common power source. The Westinghouse Engineers were using 100cps (later changed to Hz) it was Tesla that suggested 60cps, Westinghouse Engineers refused to use it but through Westinghouse Tesla managed to forced them to try 60cps. According to Tesla 60cps was the frequency of the Earth, changing to 60cps made the transformers efficient and the rest is history! From what I have also read that measured frequency of the Earth is 57Hz using modern measuring methods. Therefore 60Hz might have a slight advantage over 50Hz.

17. Diamond
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Originally Posted by Froneck
...The Westinghouse Engineers were using 100cps (later changed to Hz) .....
=) =)

Actually transformers increase in efficiency as the frequency goes up. Aircraft often use 400 Hz (aka CPS) for this reason.

18. Stainless
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Originally Posted by jim rozen
=) =)

Actually transformers increase in efficiency as the frequency goes up. Aircraft often use 400 Hz (aka CPS) for this reason.
I read what Tesla claimed. Something must have been correct since all power generation in all countries is 50 or 60Hz. I haven't heard of anyone planning or even arguing it should be increased. I know aircraft us 400 Hz, read sometime ago why but can't remember!

19. Originally Posted by Froneck
I read what Tesla claimed. Something must have been correct since all power generation in all countries is 50 or 60Hz. I haven't heard of anyone planning or even arguing it should be increased. I know aircraft us 400 Hz, read sometime ago why but can't remember!
Weight.

Tom

20. Originally Posted by JST
"Windage" in english is not "winding"...... The "windage" losses means loss due to the energy used stirring up the air. That is related to square or cube of speed, (do not recall which). Cube So a small reduction can mean a larger energy saving at lower RPM. But this is not a large loss for most equipment.

The savings in distribution at higher voltage and lower current are significant, but are nothing to do with frequency aside from 50 Hz being associated with 230 vs120 V utilization voltage for residences and offices...

But they do depend on wire size, which is an economic decision. Just doubling current (same power at half voltage) increases losses 4x. Therefore the wire resistance may be 4x larger at higher voltage with no change of losses. Choosing a larger wire size can reduce the losses, and still use a smaller mass of conductor.
The beauty of AC is that as the system demand increased, it was only necessary to increase the system voltage to increase the system capacity.

Tom

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