Answered Questions

  • Why is the transformer rated in KVA?

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    Editorial / Best Answer

    Answered by: NagaseshaReddy.M

    • Sep 10th, 2007


    kVA is the unit for apparent power. Apparent power consists of active and reactive power. Active power is the share of the apparent power which transmits energy from the source (generator) to the user. Reactive power is the share of the apparent power which represents a useless oscillation of energy from the source to the user and back again.

    It occurs when on account of some »inertia« in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only, regardless of whether it aligns with the voltage or not.

    Therefore the heat is always proportional to the square of the current amplitude, irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.

    Raghu

    • Feb 9th, 2018

    In transformer there is two losses
    1. Iron loss
    2. Copper loss
    The iron loss is depands on Voltage
    And the Copper loss is depands on current.

    Umar Naik

    • Nov 26th, 2017

    There are cu losses and iron losses which are not dependent on power factor thats why we rated it in KVA.