Efficiency of transformer

Replies

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  sau

  hii Rahul. I think that there will not be any significant change in the efficiency of transformer.As the load will change from inductive to capacitive, the output terminal voltage will increase. This may result in some increase in the iron losses and thereby decrease in the the efficiency very slightly.The regulation, however, will definitely change.There would be negative regulation for a capacitive load.
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  shubhankar

  yeah i agree with saurabh. and i would like to add a little to the discussion. when the load becomes more and more capacitive, it actually starts supplying reactive power to the supply. thus the sending end voltage in less than the voltage on the load side. weired but true. this type of load is also called as a reactive power or VAR compensator. the regulation is positive on inductive load. it goes on decreasing as the load becomes less inductive and after a point of time it becomes negative.
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  narayana murthy

  hope this may help you much
  Transformer - Wikipedia
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  rahul nehra

  but efficiency=output/input and in case of capacitive load output voltage is more than input hence efficiency should be different, this seems to be the cause of concern for me
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  baja

  I have read this question in some entrance exam books. Answer is "same".
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  baja

  @ Rahul: Efficiency of Transformer is purely bases in losses. Though Voltage and current varies There is no significant difference in losses. Hence its same.. like that i read.
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  narayana murthy

  @rahul: its impossible output never be greater than input in practical because energy neither be created nor destroyed
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  rahul nehra

  i have one more doubt as why inductive loads consume power when it has been taught that the average power consumed by an inductor in one full cycle is zero because voltage and current are out of phase by 90 degree then when inductor releases its energy then shouldnt the rotor of alternator accelerate because it is free of supplying that reactive power at this moment and input ie mechanical is greater than electrical output
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  shubhankar

  guys relax. firstly efficiency = output POWER/ input POWER. it not output voltage /input voltage.secondly,the efficiency is completely based on active power. i.e. the power which is consumed by the resistor. so even if the output voltage is greater than input, the current decreases on the output side which makes their product V X I constant. and V XI is active power. now about the inductor. though it is said that inductor consumes 0 power, but practically, the wire of which inductor is made has some resistance. that is why it consumes power. motion of the rotor is based on the supply of active power. not reactive. inductor has reactive power so no effect on the rotor speed.
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  shubhankar

  i would like to correct Mr. baja a bit. iron losses are voltage dependent and copper losses are current dependent. so it does affects the efficiency if voltage and current vary. that is why a specific current density is fixed for the windings of the transformer.
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  rahul nehra

  alternator has to supply for total power ie apparent power and not the active one and reactive power has got demagnetising effect due to which terminal voltage reduces hence the reactive power aspect should also be considered and generator has to supply for both ie active and reactive and furthermore except lightening and heating loads all other loads are inductive
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  shubhankar

  not all the reactive loads are demagnetising in nature. capacitive loads are magnetising and some loads are even cross magnetising. thus when the loads are magnetising, the alternator is called as over excited and it supplies reactive power to the supply. all the inductive loads are bound to make some or the other power loss. actually can i know your doubt about the inductors specifically?
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  sau

  what shubhankar says is 100% correct!