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How frequency effects voltage

Discussion in 'Electronic Basics' started by [email protected], Dec 27, 2005.

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  1. Guest

    I mean why we use 50/60 Hertz in houses why we dont use 400Hertz. i
    know as we increase frequency losses increase but what is formula or
    equation for that.
     
  2. Tom Biasi

    Tom Biasi Guest

    Unfortunately not every problem is solved by plugging numbers into a
    formula.
    Your question is a good one but you need to do some studying on the way
    higher frequency AC behaves in transmission lines and in every day inductors
    like drills, mixers, etc.
    You may find some interest in Edison's proposal to feed the world power with
    DC and what some rebuttals to this entailed.
    Good question, take a fun journey.
    Regards,
    Tom
     
  3. There are quite a few different factors to consider when deciding on
    the "best" power distribution frequency. In general, the transformer
    core size goes up proportional to the inverse of the frequency. So
    400 Hz transformers are about 60/400=15% the size of those for 60 Hz.
    This is an economic advantage for the higher frequency. But the
    core loss goes up as the frequency does, in two ways. There are eddy
    current losses (current that circulates in the core as if it were a
    short circuited transformer secondary) that can be reduced by making
    the laminations of higher resistivity material (most commonly, by
    alloying silicon with iron) and by making it of stacks of insulated
    laminations that are proportionately thinner.

    There are also per cycle losses related to the energy lost each time
    you reverse the direction of magnetization in iron, called hysteresis
    losses. There is nothing you can do about those, as long as you use
    iron for the core material. The exotic core materials with much lower
    hysteresis losses are a lot more expensive than the silicon iron alloy
    used for 60 Hz transformers.

    There is also the problem of phase shifts over distance that gets
    worse in proportion to the frequency. A wavelength at 60 Hz is
    something like 3100 miles. At 400 Hz, that drops to about 470 miles.
    You get into huge problems trying to connect a vast network of
    generators and consumers with transmission lines when there are waves
    of many phases propagating around all possible loops of the system,
    some places aiding and some places canceling (called standing waves).
    This makes it almost impossible to build a system with multiple
    redundant energy paths, to handle all sorts of load shifts and
    equipment failures. In effect, each state or city would have to have
    its own independent 400 Hz grid.

    I think those are the biggest factors in favor of lower frequency
    transmission of power. There are quite a few more second and third
    order factors, some of which may have applied more at the origin of
    the grid than they might, now, with advances in technology.
     
  4. pebe

    pebe Guest

    Tom Biasiwrote
    formula
    Your question is a good one but you need to do some studying on th
    way
    higher frequency AC behaves in transmission lines and in every da
    inductors
    like drills, mixers, etc
    You may find some interest in Edison's proposal to feed the worl
    power with
    DC and what some rebuttals to this entailed
    Good question, take a fun journey
    Regards
    Tom[/quote:dafa126be6
    Just a passing thought about Edison's world power feeds. There ar
    instances now where high voltage is being carried as DC on the grid
    It is used where countries with different frequency standards consum
    each other's electricity, and because it is now becoming cos
    effective because for a given maximum voltage, DC can carry about 40
    more power than AC of the same peak voltage
     
  5. John Larkin

    John Larkin Guest

    Motors. A 24,000 RPM induction motor would be hard to handle.

    John
     
  6. Sjouke Burry

    Sjouke Burry Guest

    Have worked in a place with 400Hz(military complex), wel you
    wont like it . The facility was drenched in audible harmonics,
    1200 Hz (3rd harmonic) being particulary audible.
    People working there for 10+ years had permanent damage in
    their hearing curve, and did not hear that frequency anymore.
    So no, dont do it.
     
  7. Bill Gray

    Bill Gray Guest


    Why does the military use 400Hz?

    Bill,
    Phoenix
     
  8. Ralph Mowery

    Ralph Mowery Guest

    To save weight , especially in the aircraft.
    Sometimes on the stuff that has to be carried on the backs of the ground
    forces.
     
  9. Sjouke Burry

    Sjouke Burry Guest

    Airforce facility, airforce equipment, and a bit of stupidity
    perhaps?? They had a huge flywheel/moto/dynamo/diesel running
    for conversion and emergency power.
     
  10. Pooh Bear

    Pooh Bear Guest

    Generators too !

    Graham
     
  11. But also very useful for some applications.
    You can make them run slower at the cost of more poles.
     
  12. John  Larkin

    John Larkin Guest

    But all the transformers up on the poles would go

    hhhhmmmmmmmmmmmmmmmmmmmm...

    John
     
  13. They do that now. At 400 Hz they go WHEEEEEEEEEEEEEEEE.
     
  14. That would be hard to take, having the distribution trannys "Whee"ing all
    over folks !!
     
  15. Rich Grise

    Rich Grise Guest

    Airplanes.

    The transformers are smaller, and the engine usually revs so high
    that generating 400Hz is trivial.

    I _have_ always wondered, though, if they really have that box of
    dirt in the tail section for "ground". ;-P

    Cheers!
    Rich
     
  16. Guest


    There is no as such the equation for frequency effect on domestic
    distribution system. But yes, if we are going to use the devices which
    differ form power frequency ( 50 Hz) at rated voltages ( 230 / 240
    Volts), then this will unnecessarily heat up the core of electric
    machines ( viz Motors, compressors of refrigerators, COres of
    transformers used in that circle etc).As far as usage of electronic
    devices is concerend since they are of relatively low power level, the
    effect would not be significant.

    Hope it is clear.


    M.S.Chaitanya.
     
  17. krishna

    krishna Guest

    Hi list,
    I think the electronics part of ur reply is not valid MR.
    Chaitanya.Actually the components of any ckt(electrical/electronic)
    have a tolerance limit.The rate at which they can react to application
    of voltages or rate of change of current across them.Hence almost all
    the components that are currently designed for 50/60hz would choke down
    and hence most of the ckts simply won't react so fast.Resulting in very
    fast friction at molecular level,and hence huge amt of heat
    dessipation.Hence we need to redesign our ckts.Hope the answer was
    clear.

    Open to comments.

    -kk
     
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