Information Technology Reference
In-Depth Information
2.1 Role of Capacitors
In distribution system, the fundamental function of the capacitors is to control the
fl
flow of reactive power. This can be achieved by connecting the capacitor either, in
1. Series Connections, or
2. Shunt Connections.
In series connection, the capacitors balance the inductive reactance of the circuit,
whereas, in shunt connection it supplies the reactive power or current to counteract
the out-of-phase component of current as required by an inductive load. They
modify the characteristics of the inductive load by supplying a leading current; this
counteracts the lagging currents of the loads. In series connection, the change in
inductance of the distribution lines leads to phenomena, such as, ferro-resonance in
transformer, sub-synchronous resonance during motor starting, shunting of motors
during normal operation, etc. (Gonen
1986
; Kresting
2002
). Hence, much appli-
cation of series capacitors is not observed in distribution system, yet, shunt con-
nection is extensively used. Table
1
shows the connection of the power capacitor
and the phasor diagram for both the capacitor connections. It is important to note
that the compensation provided to regulate the voltage and reactive power
fl
ow by
the capacitor is only applicable at the point of installation.
Table 1 Series connections and shunt connections of the power capacitors (Kresting
2002
)
Series Connection
Shunt Connection
Z=R+jX
l
Z=R+jX
l
I
I'
I
V
S
+
-
+
-
+
+
I
c
X
c
V
S
V
R
V
R
-
-
I
C
ʴ
ʴ
V
R
V
R
I'
I
C
I
V
c
I
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