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  • Why always MVA rating in electric machines?

    vibhor_one

    vibhor_one

    @vibhor-one-zP13jP
    Updated: Nov 18, 2009
    Views: 1.7K
    Dear All CE's,

    Please tell me why major electrical devices such as transformer, motor and generators, and also other electrical machines are rated in MVA not in MW.

    Reply soon...

    Regards

    Vibhor Mittal
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Replies

  • chirag_kotadia

    Member • Dec 2, 2009

    Re: Why always MVA rating in elect. machines?

    VA rating is the one that is indicating the complex power which contains reactive power and active power. Watt rating neglects the power factor between current and voltage while VA rating account this. Hope u r clear.
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  • cranky

    Member • Dec 5, 2009

    chirag_kotadia
    VA rating is the one that is indicating the complex power which contains reactive power and active power. Watt rating neglects the power factor between current and voltage while VA rating account this. Hope u r clear.
    Like chirag mentioned VA refers to Volt amperes rating and W refers to watt.But I guess you mentioned it incorrectly.Watt takes into account of powerfactor.We have W=VA * (power factor)

    Since the load may vary and hence the power factor(if resistive,more power factor and inductive,the otherwise) it becomes difficult to rate since power becomes dependent on load which is not what we wan't to denote.Hence,VA is preferred.

    Also,The electricity boards insist on keeping power factor high.
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  • vishu445

    Member • Dec 10, 2009

    adding to cranky, VAR stands for volt ampere reactive which is the measure of the apparent power. This power just fluctuates between the conductors and has no effect on the load. Also it earns no revenue.
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  • vibhor_one

    Member • Dec 12, 2009

    can you tell me something more var?
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  • cranky

    Member • Dec 13, 2009

    Even i would like to know..Var is Apparent power..mathematically equal to VIsin@
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  • vishu445

    Member • Dec 13, 2009

    Apparent Power is measured in terms of VAR. It will more clearer to visualize VAR on Power Loci Transmission Line. For example, consider the power circle diagram of sending end. The two coordinate axes are of MW(real power) and MVAR(apparent power). From here we can can conclude all the transmission parameters vary in terms of both real and apparent power. Also remember the fact that effects of apparent power are confined to transmission and has no effect on load.
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