- 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_{S}V_{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_{S}V_{R} Sin δ / ( X_{L} – X_{C} )………… ( 2 )

From equation ( 1 ) and ( 2 )

P’ / P = [ V_{S}V_{R}
Sin δ / ( X_{L} – X_{C} ) ] / [ V_{S}V_{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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