Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 99

WTG

A

Distribution
network

WTG

. . .

0.69/33 kV

WTG

Wind
farm

Figure 4.2 Wind farm connected to a large system through a distribution line

that the line is connected to a node at 33 kV, backed by a source or sink of zero
internal impedance and fixed frequency. This system model is known as an 'infinite
busbar'.
The main points of interest will be wind farm terminal voltage (point A in
Figure 4.2) and transmission efficiency, and the effect of power factor on both.
The relevant data for each WTG are as follows.

Rating 747 kVA

Power rating 660 kW

Voltage (line) rating 690 V

We will assume that the WTGs are connected to the 33 kV line by a 16 MVA,
690 V/33 kV transformer. The 33 kV line is 20 km long and has the parameters
given in Table 2.1. The system will be studied under full power conditions, which
give rise to the most severe voltage rise problem. Two wind farm power factors will
be considered:

unity, corresponding to the midpoint between A and B in Figure 4.1 ●

0.950 leading (consuming reactive power), corresponding to point A in Figure 4.1 ●

It is convenient to use the equivalent single phase and per unit approaches
introduced in Section 2.4. We will use the following bases:

MVA b ¼ 100
kV b ¼ 33

The line per-unit series resistance and reactance are then

R ¼ 20 0 : 30 MVA b = kV b ¼ 0 : 551
X ¼ 20 0 : 31 MVA b = kV b ¼ 0 : 569