WIND ENERGY SYSTEMS - Cd3wd

Chapter 9—Wind Power Plants 9–22
The list price is, from Eq. 8,
C 1 = 19800(20) 0.75 +1.55(350) 1.75 = $231, 150
C = 231, 150(1.3) + 3(10, 420 + 7750 + 4090) + 20000 = $387, 275
This price is then multiplied by a discount factor as quoted by the Westinghouse salesman. At the
time of this writing, this factor is 0.51, which makes the actual selling price 387,275(0.51) = $197,510.
The transformer T 2 must then be connected to the utility grid by an overhead high voltage
transmission line. This line may need to be several miles long to reach an existing line. The
cost of the transmission line will also vary with the type of terrain, the necessary current
capacity, and the local labor costs. In Kansas rough estimates for the total installed costs in
1991 dollars were as shown in Table 9.9.
Table 9.9. Overhead transmission line costs.
34.5 kV $27,000/mile
69 kV 46,000/mile
115 kV 76,000/mile
230 kV 153,000/mile
345 kV 250,000/mile
6 VOLTAGE DROP
The voltage drop in a conductor is simply IZ, whereI is the phasor current and Z is the
complex impedance. The current is known from the load requirements and the resistance is
easily calculated or looked up in a table, such as Appendix C. The reactance term, on the other
hand, is not as easy to obtain. The inductance of a wire increases as the distance to an adjacent
wire (the return path) increases. For overhead transmission lines and for multiconductor cable
(two or more conductors inside a plastic sheath) the distances to adjacent conductors are fixed,
so tables can be prepared for such cases. Windfarms, however, will have individual conductors
spaced at random in the bottom of trenches, so the exact value of reactance could only be
obtained by measurement after the trench is backfilled. This is obviously not an acceptable
solution to a design problem.
Rather than try to make an exact analysis, we will estimate the voltage drop for the
windfarm situation from the voltage drop table for conductors in conduit, as published in the
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001