WIND ENERGY SYSTEMS - Cd3wd

Chapter 9—Wind Power Plants 9–18
1 × 8forthisD dw /D cw ratio.
The 2 × 4 configuration also has the advantage of lowering the voltage drop from the
most distant turbines, and also making the low voltage drop more nearly equal among all
the turbines. The ampacity tables presented earlier deal only with heating effects and do
not answer the question as to the acceptability of the voltage drop. Voltage drops will be
considered in more detail in the next section.
The choice of low voltage configuration will also impact the distribution voltage circuit.
This is illustrated in Fig. 4 for the case of 32 turbines in 4 rows of 8 turbines each. Four unit
transformers T 1 are required in either case. The solid line shows the minimum trench length
for the 1×8 configuration. There will be parallel trenches, with the cable serving as the return
for the loop going through the transformer enclosure without physical connection. The dashed
lineshowsthetrenchlayoutforthe2× 4 configuration, with the arrows indicating a possible
location for the transformer T 2 . The bottom portion of the loop would actually be located
close to the bottom row of turbines, rather than where it is drawn in the figure. The trench
length for the 1 × 8 configuration is 6D dw ,and5D dw +8D cw for the 2 by 4 configuration.
Using the example of D dw =2.5D cw ,the2×4 requires20.5D cw while the 1×8 requires15D cw
of trench. Therefore the 1 × 8 is better in the distribution voltage trench and poorer in the
low voltage trench requirements. It appears necessary to check several possible designs before
concluding that one is superior to the others.
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Figure 4: Trench lengths for distribution voltage wiring for 32 turbines in 4 rows, for both
1 × 8and2× 4 low voltage configurations.
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001