Capacity factor Average capacity of study periodMaximum capacity
in power systems reliability evaluations。 Similar to [10], EENS is used in this paper as the reliability index。 It has been verified that the reliability assessment results using EENS in this paper are consistent with the results using hourly LOLE。
Only the results using EENS are presented。 According to [6],
In order to calculate the joint states of a wind farm, two capacity state tables need to be created first。 One is the state table of available wind。 It can be represented as a pair of
available wind capacity and its probability ( Cwnd , Pwnd ),
EENS can be calculated as。
(1)
for j = 1 to s; s is the number of wind capacity states。 The wind capacity availability and its probability can be obtained from the historical or field-measured wind profiles。 The other state table is for the capacity of available wind turbines and its probability。 The state table for the wind turbine capacity can be calculated using the forced outage rate (FOR) of wind
turbines。 The method is as same as used for conventional generator [10]。 Then the probability of a given wind farm
farm is connected to the system through two transmission lines。 The wind generation and its associated transmission
output Ck
can be obtained by:
upgrades can be modeled as a system in series connection
from the reliability assessment standpoint。
where, n is the number of states of wind turbine availability;
wtg
Pi is the probability of the wind turbine availability at
state i; U(•) is a step function。
From equation (3), it can be seen that the probability of wind capacity is the weight of the probability of wind turbine availability in calculating the probability of the joint capacity。 Then a large wind capacity factor implies that the wind turbine availability has large impact on the probability of the joint capacity, especially, under high wind conditions。 Therefore, it is necessary to evaluate and revise the wind profile by incorporating the wind turbine availability when wind
Fig。 1。 An example of wind farm interconnection
The series connection system is shown in Fig。 2。 The input and output of the series system are wind capacity and the delivered power to the main grid, respectively。 The capacity of the wind farm, transmission lines and the output of the composite system are denoted by x, y, and z, respectively。 In this series connection system, the output z is the minimum of x and y, i。e。
capacity factor is large。
C。Joint capacity of wind generation and transmission
z min(x, y)
Probabilities of x and y are denoted by Px
Interconnecting wind generation to the grid may need long distance lines since the wind resources are normally located at
respectively; hence the probability of the composite system output Pz can be obtained by
remote areas。 The transmission path between the wind
P (z) P (z) P (y) P (z)P (x)
generation and the main grid may consist of one or multiple transmission lines and reactive power support devices。