Environmental Engineering Reference
In-Depth Information
The reactive power associated with end
B
of the line is given by Equation (4.9b); hence
V
X
404
03
B
(
)
=
(
)
=
Q
=
VV
−
cos
δ
404
−
387
cos
16 7
.
44874
VAR
B
BA
.
The
Q
absorbed by the shunt reactance
X
m
= 6
Ω
is given from
2
404
6
Q
m
=
=
27 202
The total
Q
per phase is = 44 874 + 27 202 = 72 076. Hence the power factor is
72 076
150 000
cos tan
−
1
=
=
09
.
4.4.5 Induction Generator Reactive Power
Worked example 4.3 shows that the induction generator is a source of active power but a
sink of reactive power. Even when the real power output from an induction generator is zero
it will still draw considerable reactive power through
X
m
to magnetize its iron core (3
×
27.2 kVAR in the worked example). As increasing torque is applied and more real power is
exported to the network, extra reactive power is absorbed due to the reactive power consumed
by the series reactance (3
44.87 kVAR in the example). A typical relationship between
active and reactive power for an induction generator is shown in Figure 4.18.
The induction generator power factor will vary from zero at A to around 0.9 at B.
In order to improve the power factor it is often necessary to fi t local power factor
correction (PFC) capacitors at the generator terminals (Appendix). These have the effect
of shifting the overall characteristic downwards to A
×
. The amount of reactive power
'compensation' required depends on a number of technical and economic factors.
′
B
′
Q
Import
(MVAR)
B
B´
Effect of
PFC
A
A´
0
P
export (MW)
Figure 4.18
Relationship between active and reactive power for an induction generator
