Grid Integration and Power Quality - Wind Energy Systems for Electric Power Generation - page 149

a)

b)

Fig. 7.7 Required active power capability of WES supplying a high-voltage grid

7.3.3 Reactive Power and Voltage

Utility guidelines also establish regulations regarding WES capability to supply
reactive power and influence the power factor. Figure 7.8, taken from [VDN04],
extends the requirement up to 31% of the installed apparent system power. The
generator unit GU is required to serve in over-excited and under-excited condition;
the Figure indicates the dependence on voltage in form of a statics line, allowing a
hysteresis band. It is seen that the WES has to act as reactive power consumer at
over-voltage, and has to deliver reactive power at under-voltage condition by acting
as a capacitance.
Another description of the reactive power requirement in high-voltage grid, as
taken from [VDN04, Tra07], is shown in Fig. 7.9. In the Figure, called variant 2, the
voltage is connected with the power factor cos

inaclosedcurve.
Variant 1 (not shown here) covers an area of cos

ϕ

between 0,975 inductive and
0,9 capacitive (instead of 0,95 and 0,925, respectively).

ϕ