Environmental Engineering Reference
In-Depth Information
the generator loses magnets, or a mounting bolt has come loose. The difficulty,
of course, is that the continually varying blade frequency prevents simple analysis
of the data. The same is true for gearbox monitoring: for a constant speed gearbox,
spectral examination of the vibration levels can often determine which bearing is
reaching the end of its life. Advanced analytical techniques are being developed
for variable-speed monitoring that will be applied to small turbines in the near
future. On the other hand, generator temperature is easy to measure.
Condition monitoring is particularly important for remote turbines, where the
maintenance costs can be very high. In conjunction with telemetry-based web-
interfaced broadcasting it is possible to acquire and analyse data to schedule
specific maintenance for many remote sites. For grid-connected turbines, it is
likely that on-line condition and performance monitoring will become very
important, especially in those grids that have a high penetration of small-scale
renewable generators. The lifetime of many readers of this topic could well see
general web-based sharing of performance and condition information from small
wind turbines and PV installations, combined with resource forecasting, instan-
taneous demand management, and the like.
11.7 Electrical Wiring
The thickness of any wire used in the electrical system is determined by the heat
produced, the need to keep the voltage drop to less than 5%, and the need to
maintain adequate system efficiency. These problems are greatest at low voltages,
which for small wind turbines, usually occur when battery charging. Table
11.4
gives details of typical low voltage wiring losses and current capacity.
Table 11.4 Copper cable characteristics for typical battery voltages from Appendix C of AS
4509.2 for stand-alone power systems
Current carrying capacity (single phase AC or DC) using HRC fuses or circuit breaker protection
Conductor
size mm
2
Completely
surrounded in
thermal
insulation
Partially
surrounded
in thermal
insulation
Enclosed
in air
Unenclosed
in air
Buried direct in
ground or
underground
enclosures
Voltage
drop in
mV/
(Am)
1
7
10
12
16
20
44
1.5
10
16
16
20
25
29
2.5
12
20
20
25
32
18
4
16
25
25
62
40
11
6
20
32
32
40
50
7.5
10
25
40
50
50
63
4.5
16
40
63
63
80
100
2.8
25
50
80
80
100
125
1.6
35
57
92
105
115
145
1.3
50
68
110
125
115
170
0.96
70
85
140
155
170
210
0.67
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