Copyright 20 13 Dorling Kindersley (India) Pvt. Ltd

I
quadrature drop
in-line drop
v
S
v
R
δ
Fig. 7.10-4 
Phasor diagram of a line delivering power to a lagging load (Not to scale)
Therefore, reducing the reactive component of current drawn by a lagging load results in 
(i) lower current magnitude in the line and source (ii) lower line power loss and improved 
transmission efficiency (iii) lower voltage drop in the line. This reduction is effected by 
making a local capacitor act as a source of lagging reactive power required by the load. 
The line is thereby relieved from the task of supplying this reactive power. This is called 
capacitive compensation of lagging loads
. Capacitive compensation is routinely employed 
in Power Systems and Industrial Electrical Systems.
example: 7.10-4
A 230 V rms source supplies two loads in parallel. The first one draws 10 kVA at 0.8 lag power factor. 
The second one draws 10 kW at 0.8 lead power factor. Find the source current rms value, complex 
power delivered by source and source power factor.
Solution
Complex power of first load 
=
10
×
0.8 
+ 
j 10
×
sin(cos
-
1
0.8) 
=
8
+ 
j6 kVA.
Complex power of second load 
=
10 – j (10/0.8) 
×
sin(cos
-
1
0.8) 
=
10
-
j7.5 kVA.
Complex power is a conserved quantity. Therefore, complex power delivered by source 
=
total 
complex power delivered to loads 
=
18
-
j1.5 kVA. Source voltage is 230
∠
0
°
V rms. Therefore, source 
current 
=
[(18 
- 
j1.5) 
× 
10
3
/230]
*
=
78.53
∠
4.76
°
A rms.
Therefore, source current rms value is 78.53 A and source power factor is cos4.76
°
=
0.997 lead.