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 = V_SV_R Sin δ / X_L……. ( 1 )

Where V_S = Sending end voltage

           V_R = Receiving end voltage

            δ = Angle between sending end voltage and

                  receiving end voltage

           X_L = Total reactance of the transmission line

Series Compensation by Capacitor Bank

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

         P’ = V_SV_R Sin δ / ( X_L – X_C )………… ( 2 )  

From equation ( 1 ) and ( 2 )

         P’ / P = [ V_SV_R Sin δ / ( X_L – X_C ) ] / [ V_SV_R Sin δ / X_L ]

         P’ / P = X_L / ( X_L – X_C )

Now numerator and denominator is divided by X_L

         P’ / P = [ X_L / X_L ] / ( X_L / X_L  – X_C /  X_L )

         P’ / P = 1 / ( 1 – X_C /  X_L )

         P’ / P = 1 / ( 1 – K )

Where K = Degree of compensation

               = X_C /  X_L

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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