# 3phase induction motor and transformer are working on the same principle of em induction only , in motor alone why rmf is produced why not in transformer?

both 3phase induction motor and transformer are working on the same principle of em induction only , in motor alone why rmf is produced
why not in transformer?
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| both 3phase induction motor and transformer are working on the same | principle of em induction only , in motor alone why rmf is produced | why not in transformer?
The transformer is rigid with respect to both windings. When there is no current in the secondary, the magnetic field produced by the primary is limited by the primary inductance (and some slight resistance). When current flows in the secondary as a result of the voltage induced on it by the field in the transformer core, that current effectively reduces the field (since current in that direction on the secondary produces its own field of the opposite polarity). Now that the field is reduced, more current can flow in the primary. This will level out at whatever current is needed to supply power to the load attached to the secondary.
A motor will have current flowing in a winding that is nearby to a magnet or magnetic field oriented so it will attract or repel. This creates the mechanical force that can result in motion. The windings of a transformer are wound close together and are concentric with each other (even if on opposing sides of the core). There is some residual mechanical force on a transformer, but it is very small. The hum of a transformer is not from that force, but rather, it is from the constrictive effects the alternating field has on the core itself.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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First of all "rmf" is ???. I am not familiar with the term but one reference indicates that it is "rotating magnetic field". If so, then the reason is that , in the induction motor the physical design is such that a rotating field is deliberately produced- done by spatial separation of the phases around the stator. This is not done in a polyphase transformer (while the flux distribution shifts periodically it doesn't "rotate") -an exception being a polyphase induction motor at standstill.
Secondly there is more to d/dt(Li) than simply Ldi/dt which is a "transformer voltage" There is also a term (i)(dL/dt)w where w is the angular velocity- this is a "speed voltage" which is generally larger than the transformer voltage- in any motor, AC or DC, and is the voltage of concern in considering power transfer and is often called the back emf.
Does this help?
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Don Kelly snipped-for-privacy@shawcross.ca
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| |> both 3phase induction motor and transformer are working on the same |> principle of em induction only , in motor alone why rmf is produced |> why not in transformer? | | First of all "rmf" is ???. I am not familiar with the term but one
It's a term often spelled out by people that need to hunt and peck on the keyboard, but glance up while trying to type the "e" and hit the key to its right when they do.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On Mar 27, 6:38 pm, snipped-for-privacy@ipal.net wrote:

.net |

its rotating magnetic field only...
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its rotating magnetic field only... ----------------------- I realise that but as "rmf" isn't used in any of the technical texts on machines that I have or have read, I like Phil's answer better.:)
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Don Kelly snipped-for-privacy@shawcross.ca
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| On Mar 27, 6:38?pm, snipped-for-privacy@ipal.net wrote:
|> |> | | |> |------------------------------------/-------------------------------------?| | | its rotating magnetic field only...
Oh, you mean "rotating EMF" ?
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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No- rotating MMF.