Transformers in Parallel

Discussion in 'Homework Help' started by Kayne, Mar 22, 2010.

  1. Kayne

    Thread Starter Active Member

    Mar 19, 2009
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    The question is, two 100kW transformers are connected in parallel and are supplying a common load of 180kW at a power factor of 0.9. The per unit impedance transformer A is (0.5+j8) and impedance of transformer B is (0.75+j4). Calculate the kW supplied by each transformer.

    I have done the question which can be seen on the attachments. I am wanting to know if I have done this correctly?

    Thanks for you help
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    I notice no one responded to this.

    My solution attached. I've assumed lagging power factor - which wasn't explicity stated in the question.
     
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    Last edited: Mar 25, 2010
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  3. Kayne

    Thread Starter Active Member

    Mar 19, 2009
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    Thanks for the replay, you have done it a different way to me so i will go back and have another look at your workings.

    Thanks again
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Looking at your posted solution it's clear where you went astray.

    You assumed that the load apparent power is absorbed by the combined equivalent series impedance of the two transformers - which cannot be the case. Your deduced voltage 697.13 @ 275.69° is therefore incorrect.

    This is not the correct approach to a solution. You don't have sufficient information in the question to deduce the actual voltage or current values. You only have the transformer per unit impedances to work with.

    As my posted method shows, you can find the power delivered by each transformer without the need to find either voltage or current as an intermediate step.
     
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  5. Kayne

    Thread Starter Active Member

    Mar 19, 2009
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    Thanks TNK, Yes I did assume that which was incorrect, I thought that by finding the voltage this would help in the solving of the problem. I found the formula that you used in a text book so I now in future will use this one.

    Thanks again
     
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