08/10/2020

Series Compensation

 

  • The power transfer capability of the Extra high voltage ( EHV ) transmission line is improved by series compensation. 
  • The series capacitors are connected in series with the line at any suitable location and compensate partly or totally effect of inductance reactance of the line. 
  • The power transfer capability of the transmission line is given by

              P = VSVR Sin δ / XL……. ( 1 )

Where VS = Sending end voltage

           VR = Receiving end voltage

            δ = Angle between sending end voltage and

                  receiving end voltage

           XL = Total reactance of the transmission line

Series Compensation by Capacitor Bank

  • When a capacitor of reactance XC is inserted in series with the transmission line, net reactance becomes equal to XL – XC. Therefore the total power transfer capability is equal to

         P’ = VSVR Sin δ / ( XL – XC )………… ( 2 )  

From equation ( 1 ) and ( 2 )

         P’ / P = [ VSVR Sin δ / ( XL – XC ) ] / [ VSVR Sin δ / XL ]

         P’ / P = XL / ( XL – XC )

Now numerator and denominator is divided by XL

         P’ / P = [ XL / XL ] / ( XL / XL  – XC /  XL )

         P’ / P = 1 / ( 1 – XC /  XL )

         P’ / P = 1 / ( 1 – K )

Where K = Degree of compensation

               = XC /  XL

Therefore the power transfer with series compensation is given by

          P’ = [ 1 / ( 1 – K ) ] P

Where P’ = Power transfer with series compensation

            P = Power transfer without series compensation

Let the line is compensated by 30% i.e. K = 0.3, the power transfer capability increases by 42%

                             P’ = P / ( 1 – K )

                             P’ = P / ( 1 – 0.3 )

                             P’ = 1.42P

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