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@naveee • 07 Dec, 2012 • 1 like

Can someone tell me why is transformer efficiency is higher than motor and generator? Transformer efficiency is generally greater than 95%, while that of the motors its ~70%. Both are electrical machines, so why's such a difference between the efficiencies?

PS: Edited By Admin. Added more description to make the question clearer to understand.

@Abhishek Rawal • 07 Dec, 2012 • 1 like Transformers has copper & core loss.
Motor or Generator has Mechanical loss (Friction loss & Windage), Core loss (Stator core & Rotor core) & Copper loss (Stator Cu & Rotor Cu).
Hence Generator/Motor has less efficiency than transformers.

I will suggest you Electrical Machines by B.L.Theraja .It's like Bible for me for EM.However I don't have any problem in answering the question 😀
@pinank • 09 Dec, 2012 • 1 like generally the copper loss are negligible in AC machines as the reluctance is much more than the resistance.. so taking this into consideration the transformers have core loss bt motors and generators have frictional in mechanical the efficiency of transformers is higher!
@zaveri • 09 Dec, 2012 • 1 like Maybe i think ANISH PETER and pinank have a point

motors and generators have moving parts, and frictional losses as well as transmission losses at the bearings take place, which however do not take place in a transformer.
@Jeffrey Arulraj • 09 Dec, 2012 • 1 like All the same comes Harmonic generation in rotating parts loss in harmonics are also prevalent in these rotors reducing efficiency rapidly
@Henri • 10 Dec, 2012 • 2 likes generally,most of the energy losses in transformers are minimized effectively and again they are few,,,for instance eddy currents being minimized by use of soft iron core.....but motors and generators have so many energy losses especially due to moving parts,,remember transformers are kind of static with only flow of energy taking place whereas motors are dynamic and with lots of moving parts...considering friction and other factors makes them less efficient
@revathi.geeda • 15 Oct, 2015 efficiency of transformer is higher than that of motors why??
@sunil kumar singh • 16 Nov, 2015 • 1 like As the transformer is a static device so the windage and cupper losses are not present ,but motor or generator are not static device so windage and cuuper losses are present ,therefore the efficiency of motor or generator is less than the transformer,in transformer only cupper and core losses are present and its effinciecy is more than 95% and the effinciecy of motor or generator is approx. 70%...
@MANISH KUMAR • 13 Dec, 2018 • 1 like

The efficiancy of trasformer is high because there are no dynamic losss it is a static device

@Durgesh Srivastava • 31 Jan, 2020

The  transformer is more efficient because , there is no moving device to lose energy mechanically as in case of DC motorsand generators , there is no air gap between two coils transferring energy in a transformation and there is no loss of energy in making AC to DC and DC to AC by using convertor or commutators  and carbon brushes

@Kavya Burramolla • 02 Feb, 2020 • 2 likes

Adding one more point to the discussion, the main difference between the transformer and motor is that its structure and performance, transformer has primary and secondary winding used to set up or set down the supply voltage or current at the output. Whereas motor is made of stator and rotor which when excited with input electrical energy converts into mechanical energy. 

Coming to the efficiency due to the copper losses and frictional losses which is more in motor the efficiency of motor is less than that of transformer whose copper loss is less. 

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