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  • #10541
    ritesh giri

    What are the advantage and disadvantages of reactive power?

    How does it affect power transmission?









    Spir Georges GHALI

    Dear ;


    First, all equipments that contain a ” Reactance ” like ” Motors, Transformers, … ” and are working on ” AC power supply ” need absolutly the Reactive power, and this reactive power is depending on the specifications of these equipments. Exp. if there's 2 motors have the same value of the active power but for the 1st ” Cos φ = 0.80 ” and for the 2nd ” Cos φ = 0.85 “, the 1st motor needs as reactive power more than the 2nd motor. Noting that the Reactive power doesn't transfer to any kind of work, for exp. only the active power of a motor will be transferred to a mechanical work.


    The most disadvatages of a big reactive power are :

         – The invoice of the consumed reactive energy will be important.

         – A big Jule's losses.

         – The Voltage Drop will be also big specially in the transmission lines as their distances are important.

         – For a source ” P² = S² – Q² “, so, as the Reactive power increase, the available active power decrease.


    For these reasons, and as we can't do any thing for the consumed reactive power of equipments, we try to improve always the value of ” Cos φ ” for the networks, when doing, the advantages are :

         – Decrease the amount of the invoices.

         – Decrease the Jule's losses.

         – Decrease the Voltage Drop specially on the Transmission lines.

         – More available of Active power for a source.


    The mechanical input of a generator is always constant therefore the real power output is constant. However, a large amout of reactive power will cause the apparent power to increase with the real power held constant. This means more amps and therefore higher copper losses in the transmission lines.

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