Synchronous Condenser and Power Factor Correction

Synchronous Condenser ( or ) Synchronous Capacitor :

     If Synchronous motor is on no-load and over excited ( Eb  >  V ) then the current drawn by it leads the voltage by nearly 90°. Phasor diagram of the motor at no-load is shown below. Therefore at this condition when an synchronous motor is over excited it is called as synchronous condenser. 

     The characteristics of a synchronous motor at this instant will equal an capacitor. Hence as the capacitor, an over excited synchronous motor can be used as an power factor correction device.

Synchronous Condenser and Power Factor Correction

Power Factor Correction :

     As we seen in industries most of the motor used are of induction motors and load such as lights, fans, heaters etc will draws lagging currents. This lagging currents will decreases the power factor of the whole unit due to large reactive component. Hence overall efficiency of the system may decreases.  

Synchronous Condenser and Power Factor Correction

     The power factor correction is possible by using synchronous motor ( Operating on no load with over excitation ) in parallel with induction motors or transformers, the leading reactive volt amperes supplied by the synchronous motor compensate for the lagging reactive volt amperes of other power apparatus. By this way, synchronous motor as a synchronous condenser is helpful in improving overall power factor of the system.

Synchronous Condenser and Power Factor Correction

     The figure above shows the phasor diagram of a arrangement for improving the overall power factor of the electrical system using of a synchronous system.

     The subscript ' 1 ' refers to the induction motor ( lagging ) load. the subscript ' 2 ' refers to synchronous motor and subscript ' T ' to the total load.


    kVA1kW1, and kVAR1  =  Apparent active and reactive powers of induction motor load, 

    kVA2, kW2, kVAR2 = Apparent, active and reactive power of synchronous motor,

    kVAT,  kVART,  kW =  Total apparent, active and reactive loads.

     It is seen that the addition of synchronous motor improves the power factor from Cos φ1, to Cos φT  

Sign Convention  :  Lagging kVAR is taken as ' -ve ' and leading kVAR is taken as ' +ve ' sign 

kW of the combined ( or ) total load,

kWT   =  kW of the load  +  kW of the synchronous motor

=   kW1  +  kW2

kVAR of the synchronous motor,

kVAR2  =  kVAR of the combined load  -  kVAR of the load

=  kVART  - kVAR1

kVA rating of the synchronous motor,

kVA2  =  (  kW2  )2 + ( kVAR2 )2

Power factor of the synchronous motor, 

Cos φ2  =  kW2 / kVA2

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