Fig。 3 shows that the EENS increases rapidly as the load increases。 In order to maintain system reliability, conventional capacity is added into the system。 In this example, assume  the

L is the frequency of line related failure,

occurrence/year/mile, normally is given in per 100 miles;

L is the length of a line, mile;

rL is   the   mean   duration   of   line   related     failure, hour/occurrence;

T is    the    frequency    of    terminal   related failure,

occurrence/year;

rT is  the  mean  duration  of  terminal  related     failure, hour/occurrence;

T is the hours of a cycle, e。g。 8760 hours of a year。

D。Benefit/cost assessment of de-rated transmission upgrade

The benefit of using de-rated transmission mainly is the saving on transmission investment。 From the standpoint of system reliability however, the de-rated transmission upgrade may reduce the contribution of wind generation to system reliability improvement。 A benefit/cost assessment therefore is needed to determine the optimal capacity of the transmission upgrade for wind generation interconnection。 The cost may include additional conventional capacity that is needed to maintain system reliability, and the additional wind  capacity to meet the mandatory RPS target。 Additional transmission upgrade for the higher capacity may also be needed。 The reliability approach proposed in this paper can be used to identify the cost of de-rated transmission upgrade, which will be discussed in detail in the following section。

III。Reliability Assessment of a Wind Resource

E。Reliability cost of wind integration

The   IEEE-RTS   [13]   system   is   used   in   this   paper    to

capacity of the additional units is 25 MW and the FOR is 6。3%。 The addition of wind generation and conventional capacity that are needed to meet the 6% RPS target and to maintain the system reliability are shown in Fig。 4。 It can be seen in this example that the addition of conventional capacity increases rapidly and will be more than the new wind generation when the peak load exceeds certain level。 This implies that the wind penetration is limited for a particular system depending on the peak load, which is shown in Fig。 5。

TABLE I。 WIND ENERGY AVAILABILITY AND THE PROBABILITY

% of Capacity Probability

0 0。0933332

8 0。0162963

20 0。0192593

30 0。0222222

42 0。0251852

56 0。0059259

70 0。0118519

84 0。0029630

  100 0。8029630

BASE CASE PEAK LOAD