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Q: AC Power Supply: 50 Hz or 60 Hz? ( Answered 5 out of 5 stars,   7 Comments )
Question  
Subject: AC Power Supply: 50 Hz or 60 Hz?
Category: Science
Asked by: probonopublico-ga
List Price: $5.00
Posted: 19 Nov 2002 12:14 PST
Expires: 19 Dec 2002 12:14 PST
Question ID: 110766
I believe that it was Tesla who decided that 60 Hz was the right
frequency for AC power distribution in the US and that, later, some
British guru decided that it should be 50 Hz.

We are, of course, still having to live with this difference but what
are the advantages of one frequency over the other? Or doesn't it
really matter?

Request for Question Clarification by shivreddy-ga on 19 Nov 2002 14:25 PST
Hi,

I would be most happy to answer this question for you. Before I
officially answer your question, I would like to know if the following
explanation would suffice. Please indicate accordingly and I will post
it as a final answer.

The supply of electric power to our houses from generating stations is
mainly in the form of alternating current(a.c.). However the losses
experienced along the path of travel from the central power grid
station to the sub-stations and then on to the distributors are
phenomenal. This loss is dependent on the frequency of the a.c.
supply. Along the path there are transformers, transmission cables and
cores. The loss of energy in these parts depend directly on the
frequency irrespective of whether the voltage is being stepped down or
up.

Note: Static hysteresis loss is proportional to frequency. An equation
called Steinmetz equation can be employed to arrive at the fact that
60 Hz supply causes more dissipation of heat and energy than 50 Hz
systems. Hence it is not preferred by many countries. The losses being
proportional to the square of the frequency, is hence very high for 60
Hz systems.

Now to understand the geographical areas of usage consider this
extract,
"North American 110-120 volt electricity is generated at 60 Hz.
(Cycles) Alternating Current. Most foreign 220-240 volt electricity is
generated at 50 Hz. (Cycles) Alternating Current...tape and CD
players, VCR/DVD players, etc. will not be affected by the difference
in cycles. IMPORTANT: Voltage converters and heavy duty transformers
do not convert cycles."
Modifying Foreign Electricity: "What You Should Know About Traveling
Overseas With Electrical Appliances" Copyright  2001 Hybrinetics,
Inc.
http://www.voltagevalet.com/foreign.html

To answer your question specifically, there are no clear advantages of
60 Hz over 50 Hz except in a few cases like the one on video graphics
I have considered below. Similarly 50 Hz supply which is used in India
also is not of much advantage. The two systems are now standards and a
transformer is requried to step up or step down from 220 to 110V or
vice versa. Sometimes the difference between the two frequencies are
not significant.In general, the three phase motor at 50 Hz can run
also at 60 Hz, increasing the voltage of 15%, the motor at 60Hz can
run also at 50 Hz decreasing the voltage of 15%, but without the
tolerance  10% expected in the version at 50 Hz.

An article with reference to effects of frequency on video display can
be found here,
http://members.ams.chello.nl/d.wolthers/60.html


Additional Links:

If you are mathematically inclined, you can see how the results in the
first part of the answer were reached here:
http://thayer.dartmouth.edu/other/inductor/gse.pdf

A good paper which considers the effect of frequency differences on
transformers can be found here,
http://www.mag-inc.com/pdf/TWC-500p16-17.pdf

Another paper on low frequency (30-80 Hz) trnsformers can be found
here
http://www.semiconductors.philips.com/acrobat/applicationnotes/ECO7703.pdf

regards,
Shiv Reddy
Answer  
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
Answered By: shivreddy-ga on 19 Nov 2002 21:34 PST
Rated:5 out of 5 stars
 
Hi,

After further researching your question, I have come to realise that
barring a detailed look at the effects on motors, I have covered
almost all aspects of the subject. I am therefore posting it as the
'official' answer(a section is appended on motors). If you need a
clarification regarding any part of the answer, I will be happy to
oblige.
 
The supply of electric power to our houses from generating stations is
mainly in the form of alternating current(a.c.). However the losses
experienced along the path of travel from the central power grid
station to the sub-stations and then on to the distributors are
phenomenal. This loss is dependent on the frequency of the a.c.
supply. Along the path there are transformers, transmission cables and
cores. The loss of energy in these parts depend directly on the
frequency irrespective of whether the voltage is being stepped down or
up.
 
Note: Static hysteresis loss is proportional to frequency. An equation
called Steinmetz equation can be employed to arrive at the fact that
60 Hz supply causes more dissipation of heat and energy than 50 Hz
systems. Hence it is not preferred by many countries. The losses being
proportional to the square of the frequency, is hence very high for 60
Hz systems.
 
Now to understand the geographical areas of usage consider this
extract,
"North American 110-120 volt electricity is generated at 60 Hz.
(Cycles) Alternating Current. Most foreign 220-240 volt electricity is
generated at 50 Hz. (Cycles) Alternating Current...tape and CD
players, VCR/DVD players, etc. will not be affected by the difference
in cycles. IMPORTANT: Voltage converters and heavy duty transformers
do not convert cycles."
Modifying Foreign Electricity: "What You Should Know About Traveling
Overseas With Electrical Appliances" Copyright  2001 Hybrinetics,
Inc.
http://www.voltagevalet.com/foreign.html 

To answer your question specifically, there are no clear advantages of
60 Hz over 50 Hz except in a few cases like the one on video graphics
I have considered below. Similarly 50 Hz supply which is used in India
also is not of much advantage. The two systems are now standards and a
transformer is requried to step up or step down from 220 to 110V or
vice versa. Sometimes the difference between the two frequencies are
not significant.In general, the three phase motor at 50 Hz can run
also at 60 Hz, increasing the voltage of 15%, the motor at 60Hz can
run also at 50 Hz decreasing the voltage of 15%, but without the
tolerance  10% expected in the version at 50 Hz.

In a motor, Eddy current losses can be examined as follows,
Pe~f**2, i.e. they will increase by 44% from 50 to 60Hz.
               note: ~ indicates 'proportionality'

For Hysteresis losses (C.P. Steinmetz Equation/Law):
Ph~f**1.6, i.e. they will increase by 33.9% from 50 to 60Hz. The
exponent varies from 1.4 to 1.8; however, it is generally accepted as
1.6.


These losses described above produce heat that has to be removed.
Accordingly one might be forced to conclude that 60 Hz systems are
more lossy. However if you consider the output power and efficiency,
50 Hz systems are at a very slight disadvantage.

More on this can be found here, an extract:
"Pm(50) is the mech power required at 50Hz.
Pm(50)=T*wm(50) where T is the torque and wm(50) is the angular speed
at 50Hz.
At 60Hz, wm(60)= (60/50)*wm(50) = 1.2*wm(50) so the motor runs 1.2
times more than at 50Hz....If the efficiency is constant, then A(60)=
(1.2/0.9) A(50)=1.33 A(50)the apparent power increases of 33%..."
Eng-tips Forums: "50 and/or 60 hz motor running suitability." Initial
post by dubairay. Post by Alex68 on Sept 12, 2002.
http://www.eng-tips.com/gviewthread.cfm/lev2/11/lev3/47/pid/237/qid/31684

 
An article with reference to effects of frequency on video display can
be found here,
http://members.ams.chello.nl/d.wolthers/60.html 
 
 
Additional Links: 
 
If you are mathematically inclined, you can see how the results in the
first part of the answer were reached here:
http://thayer.dartmouth.edu/other/inductor/gse.pdf 
 
A good paper which considers the effect of frequency differences on
transformers can be found here,
http://www.mag-inc.com/pdf/TWC-500p16-17.pdf 
 
Another paper on low frequency (30-80 Hz) trnsformers can be found
here
http://www.semiconductors.philips.com/acrobat/applicationnotes/ECO7703.pdf


Search Strategy:

50 Hz 60 Hz difference
50 Hz 60 Hz advantage(s)


I hope the above answer is satisfactory. 

Thank you.
 
Regards, 
Shiv Reddy
probonopublico-ga rated this answer:5 out of 5 stars
Hi, Shiv & Neil

My thanks to you both for your answer & comment: I was unaware of the
matters that you have raised.

With reference to India, I recall one visit to Bombay when the city
had no electricity. I was told that they used a coal-fired generator
but that they had run out of coal. Unfortunately, they couldn't get
coal to the power station for a time because it was usually brought in
by rail, along an electrified line.

Kindest regards

Bryan

Comments  
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: neilzero-ga on 19 Nov 2002 17:07 PST
 
A very few people are adversely affected by floresent tubes powered by
60 hz. The number may double at 50 hz, but I am speculating. Almost
everyone is adversly affected by a single floresent tube powered by 25
hz or lower frequency as it perceived as a stobe light. Two or more
phase shifted floresent tubes reduces this problem. The construction
of the world's most powerful alternator would be more difficult and
costly at 60 hz than at 50 hz, but the cost is essentialy the same for
alternators almost that powerful. On the average, motors and
transformers for 50 hz are slightly heavier and slightly more
efficient than the same rating for 60 hz and the motors typically run
at 5/6 the speed of 60 hertz moters. This can be either a minor
advantage or minor disadvantage. The pain of electric shock increaces
as the frequecy is lowered, possibly the probability of death. Hum is
more dificult to reduce, but the sensitivety of the human ear to hum
decreases with frequency, so that is about a tradeoff.   Neil
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: roval-ga on 27 Nov 2002 10:52 PST
 
Do you want a clear answer: “Yes, this frequency is better than the
other one!”?
There is no such answer!
You can go in details (in different areas of electrical activity) and
find advantages and disadvantages.
shivreddy-ga explains how the loss of power increases for 60Hz systems
comparing with 50Hz systems. We can say that is better at 50Hz. But
talking about fluorescent tubes it is preferred to have 60Hz (harder
to see the flickering). And, considering the explanation you received
about the motor designed for 50Hz and running at 60Hz, I can tell you
that is pure speculation. Nobody (that considers himself a
professional) will ever do something like that. You CAN mix them up
but it is NOT RECOMMENDED to do it!
So which one is better? Overall talking they are about the same.
But, if they have no clear advantages over the other one, why do we
have two of them? I don’t know exactly, but it is very possible to
have “historical” reasons!
It is very possible to have political reasons: somebody decided to
have a different value to prove he is different comparing with
somebody else (ex: USA – England, 200 years ago). And being different
can be interpreted as independent.
It is possible to have “economic” reasons: somebody decided long time
ago to interdict certain products coming from a country they didn’t
like (to "protect" the market). Having a different standard was an
easy way to justify such a "protective" measure.
But all these are politics. Let’s come back to technical stuff.
You asked about frequency differences. What about voltages? Here there
is a clear answer: 220-240V is better than 110-120V. There are
different reasons. Major one is power loss. When running 120V you have
4 TIMES more power loss in the distribution grid comparing with
running same equipments on 240V. Plus you need thicker wires
everywhere, better switches to connect / disconnect equipments, etc.
As (almost) everybody knows: Power = Voltage x Current. For the same
power: the lower the voltage – the higher the current. And, higher the
current, more problems you have.
Conclusion: There is no clear difference between 50Hz and 60Hz from a
technical point of view.
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: shivreddy-ga on 27 Nov 2002 12:01 PST
 
Hi,

roval-ga, yes I totally agree with you. There isnt ANY clear
difference between 60Hz and 50Hz.  In India where I  live it is 50Hz
220V - 240V and this system has its own advantages.... In the US it is
110V and 60Hz why? I dont know perhaps you could tell me?

Regards,
Shiv Reddy
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: probonopublico-ga on 27 Nov 2002 23:15 PST
 
Hi, Roval

Many thanks for your helpful comments.

There are always 'good' commercial reasons that need to be considered.

kindest regards

Bryan
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: vinods-ga on 04 Dec 2002 11:43 PST
 
Hi probonopublico, 

<There are always 'good' commercial reasons that need to be considered.>

Would you please explain what you mean by this?

warm regards
vinods-ga
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: lookfwd-ga on 14 Dec 2002 17:34 PST
 
There is something we should always have in mind. There may be no
important difference between 50Hz and 60Hz but it is more than
important to be standardized and stable.

There are a lot of devices that are optimised and in fact working in
either one of these frequencies. One of the most important is video,
which sometimes retrieve their clock frequency from AC voltage and
some clocks that do the same. I live in Greece and the voltage level
is 240 V although typically it should be 220V and the frequency is not
so stable as well. This causes a lot of trouble. Some PC power supply
units get burned, some clocks don’t work and of course a video player
that came (with the appropriate TV set) from Canada, couldn’t work
although we have provided it the 220V to 110V transformer. As you can
see its very important to hold the voltages and frequencies between
the typical levels.

* You may think that 240 V is typical but we shouldn’t forget the 5%
error rate. This means that once having 240 V AC you could also have
20 seconds with 245 V. This is something that many producers forget
for their money’s sake.
Subject: Re: AC Power Supply: 50 Hz or 60 Hz?
From: probonopublico-ga on 14 Dec 2002 20:48 PST
 
Hi, Lookfwd

An interesting point!

Many thanks for your contribution.

Kindest regards

Bryan

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