Transmission Expansion Planning in Deregulated Power ... - tuprints

4 Market Based Criteria 32
4.2 Market Based Criteria
Fig. 4.1 – Line No. i of a network
In this section two probabilistic criteria, average congestion cost and standard deviation of
mean of LMP, are proposed to measure how much a specific plan facilitates competition
among customers. Average congestion cost shows how intensive transmission constraints are
and consequently shows how competitive electric market is. Standard deviation of mean of
LMP shows how mean of LMP spreads throughout the network. Therefore, it shows how
discriminative and consequently how competitive electric market is.
4.2.1 Transmission Congestion
A line is congested if its power has reached to its limit. Transmitting more power through this
line is not allowed. In other words, a line is congested if its associated constraint in (3.3) is
active. Under transmission congestion next MW of some loads can not be supplied by the
cheapest undispatched generation. The next MW of these loads, depending on their places in
the network, is supplied by other more expensive generations. Hence, under congestion buses
have different LMPs.
Congestion cost of a line is defined as the opportunity cost of transmitting power through it.
Consider figure 4.1, line i of a network is depicted in this figure. The end buses of this line
numerated with i1 and i2.
Pl MW electric power transmits from bus i1 to bus i2 through this
i i
1 2
line. LMPs of buses i1 and i2 are
lmp i and
1
lmp i in $/MWhr. Buying 1 MW electric power
2
from bus i1 costs lmp i $/hr and buying 1 MW power from bus i2 costs 1
i2
lmp $/hr. Therefore,
the opportunity cost of transmitting 1 MW electric power from bus i1 to bus i2 is equal to
( i2
i1
lmp − lmp ) $/hr. Thus, congestion cost of line i or the opportunity cost of transmitting
Pl MW electric power from bus i1 to bus i2 through line i is equal to:
i i
1 2
lmp i
lmp
1
i2
i1
Pl i i
1 2
Line No. i
i2