Power system fundamentals - Wind Power Integration: Connection and System Operational Aspects - page 50

I

V g

j X I

V

R I

Figure 2.28 Voltage regulation for active power

V

R I

V g

j X I

I

Figure 2.29 Voltage regulation for reactive power

Now consider reactive power generation. Positive reactive power consumption
for a load implies current lagging voltage by 90 . Adoption of the generator con-
vention reverses the current phasor. Positive reactive power generation reverses it
again. This is depicted in the phasor diagram of Figure 2.29.
It may be seen from Figure 2.29 that the voltage rise due to reactive power
generation is given approximately by

XV g I
V g ¼

XQ
V g

D V r XI ¼

The total voltage rise from generation is given by

RP þ XQ
V g

D V ¼ D V a þ D V r ð 2 : 24 Þ

Equation (2.24) can be used iteratively to estimate the generator voltage. For
example, we could:

1. set V g ¼ 1.0 pu
2. obtain D V
3. set V g ¼ 1.0 þD V
4. if V g is within a given tolerance of its previous value, exit; otherwise return to
step 2

This is a primitive example of a load flow problem.