WIND ENERGY SYSTEMS - Cd3wd

Chapter 9—Wind Power Plants 9–17
to four turbines in one row and four in the adjacent row? We will try to answer this question
by example to illustrate the procedure for other configurations.
Figure 4 shows the trenches needed for the 8 turbines connected in one long row or two
short rows. The transformer T 1 is physically small compared with D cw , and so is the separation
between adjacent trenches. Such small corrections will be ignored in this analysis, but
allowance should be made for splices, connections, vertical runs of cable, and crooked trenches
when actually ordering the cable. The two turbines nearest to T 1 require a trench length of
only 0.5D cw in the 1 by 8 configuration, but the two most distant turbines require a trench
length of 3.5D cw . Separate trenches are required because of heating effects. The total trench
length for this configuration is then 16D cw .
✲
D cw
✛
✈
✈
✈
✈
✈
✈
✈
✈
T 1
(a) D T =(1+3+5+7)D cw =16D cw
✈ ✈ ✈ ✈
❅ ❇ ✂
❅ ❇
❅ ❇
❅ ❇
❅ ❇
❅❇
T 1 ❅❇
❇❅
❇ ❅
❇ ❅
✈ ✂✈ ✂✂✂✂✂✂✂✂✂✂✂ ❇ ❅
❇ ❅
❇✈ ❅✈
√
(b) D T =2
√D cw 2 + D2 dw +2 (3D cw ) 2 + Ddw
2
✻
D dw
❄
Figure 3: Trench lengths for low voltage wiring for 8 turbines in 1×8 and2×4 configurations.
When the turbines are connected in a 2 × 4 configuration, the nearest turbines require a
greater trench length while the most distant turbines require shorter trenches than the most
distant turbines of the 1 × 8 configuration. Simple square roots are used to find the trench
lengths, with the formula for this particular case shown in Fig. 3. No universal comparison can
be made without knowing both D cw and D dw , or at least their ratio. For the case where the
downwind spacing is 2.5 times the crosswind spacing, the trench length for this configuration
is 13.2D cw , an 18 percent reduction from the 16D cw of the 1 by 8 configuration. This reduces
both first cost and operating cost by reducing losses, so the 2 × 4 would be preferred over the
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001