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Why in electric machines we don't care of electric field but magnetic!

  1. Feb 12, 2013 #1
    why in electrical machines we says that magnetic field transfer energy in air gap
    but isn't there electric field also in air gap !!!!
     
  2. jcsd
  3. Feb 12, 2013 #2
    Re: why in electric machines we don't care of electric field but magne

    no, electric field is generated when a magnetic field moves across an inductor.

    for example, two sides of a transformer are separated by a gap, there is magnetic induced, but there is no electrons being transferred.
     
  4. Feb 12, 2013 #3

    NascentOxygen

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    Re: why in electric machines we don't care of electric field but magne

    If you look at the geometry of a motor, you'll see that the air gap exists between the steel poles of the stator and the steel of the rotor. These steel faces are at ground potential; there is not much potential difference across that gap.
     
  5. Feb 13, 2013 #4

    gerbi

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    Re: why in electric machines we don't care of electric field but magne

    (Thread title) We take care about electric field in electric machines. It's alayzed to provide sufficent degree of protection - by the means of electrical insulation. Insulation system is one of the most important ones - it limits machine design a lot.

    Why magnetic and not electric field in the air gap ? First of all, it's electromagnetic field (combination of both electric and magnetic).
    What is the puroouse of this whole magnetic core in machine design? Why magnetic core is so much connected to the power of machine (generally, bigger machine=bigger core)? Power is transfered between stator and rotor coils by magnetic flux. Air gap is just one of the elements in this 3D magnetic circuit. Magnetic coupling of coils (or magnets etc.) combined with rotation makes this all a working mechanism.
     
  6. Feb 13, 2013 #5
    Re: why in electric machines we don't care of electric field but magne

    does u mean there is no elctric field at gap !!!!!
    if yes! isn't electric field at conductor =0 then electric field exist outside conductors then it's electric field at gap !


    how it's ???
    why and how the surfaces grounded??


    I didn't understand u
    I'am asking about why the electric field doesn't play a role in machines not the insulation
    why magnetic flux not electric field
     
  7. Feb 13, 2013 #6

    NascentOxygen

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    Re: why in electric machines we don't care of electric field but magne

    In a motor, it is arranged that the magnetic field can follow a closed path of steel (except for the air gap) to maximize efficiency. For convenience, and for safety, all of that steel is at ground potential. There is no reason for it not to be. The electric conductors are all insulated from the steel, for safety. As a consequence, there exists zero or very slight electric field between areas of steel.
     
  8. Feb 13, 2013 #7

    sophiecentaur

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    Re: why in electric machines we don't care of electric field but magne

    In a normal electric motor, what "gap' is the electric field supposed to develop across and where is there a charge to experience a force due to this field? Any electric fields that might occur inside a magnetic motor will be zero or negligible. What does count, however is the Potential Difference across the terminals of the commutator which defines the Power obtained per Amp of current flowing in it. The actual 'volts per metre' over the length of the armature winding is very low and, in any case, because the windings are in a coil, the net effect of any field will be zero.
    It would be difficult to imagine a suitable design for a rotating motor which is based on electric fields. That's the beauty of a Magnetic motor: the force is at right angles to the conductor and the field so it instantly gives you a tangential force to turn your motor. Plus, you can have a very small gap over which to develop a nice high magnetic field.
    An electric-field driven motor would need to be reciprocating and with a very small 'throw' if you wanted to have a high field.
     
  9. Feb 13, 2013 #8

    sophiecentaur

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    Re: why in electric machines we don't care of electric field but magne

    They are both connected to the case of the motor and to each other by the bearings. No significant PD can develop across the gap.
     
  10. Feb 14, 2013 #9

    gerbi

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    Re: why in electric machines we don't care of electric field but magne


    Stator and rotor coils are connected magnetically via flux ("electric" refers only to source of energy powering the machine). This is your answer.
    Why like this ? Because someone smart invented this and made it working.
    //And please, formulate topic names more fortunately.
     
    Last edited: Feb 14, 2013
  11. Apr 6, 2013 #10
    so, electric field doesn't contribute in energy transfer or what??

    that I'm asking about
     
  12. Apr 6, 2013 #11

    sophiecentaur

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    No, is the answer. Any electric forces would not contribute to any significant extent (either to enhance or reduce the magnetic forces). Why would you want it to? You must have a reason, presumably, or is it just because of the word "electromagnetism"?
     
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