The Emerging Electrical Markets for Copper
Figure 52: The Increasing Size of Wind Turbines
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- Figure 53: Cables Employed in an Onshore Wind Power System
Figure 52: The Increasing Size of Wind Turbines
The design of the working components of wind towers has improved over time. Wind generators are required to produce electricity at wind speeds of 4 to 25 metres per second, shutting down above this speed for reasons of safety. Efficiency improvement has focussed on electricity generation at low wind speeds. Reliability, low noise and grid compatibility are essential design features of wind towers. Most existing wind turbines incorporate a gearbox between the rotor and generator. The gearbox can be considered the weakest link in wind turbine design. It is used to convert the relatively slow speed of the rotor to that required by the generator, and was necessary in early constant speed rotor systems. Using constant speed rotors is inefficient, but is necessary if there is a direct feed of power to the generator from the grid. Partial decoupling from the grid, allowing the speed of the rotor to vary, came in with the use of power electronics, thus reducing the strains on the gearbox. Full decoupling, achieved with modern direct drive synchronous systems, dispenses with the gearbox altogether. The developments in turbine technology have meant the creation of a large market for power electronics, and changes in generator design. The traditional design, used with constant speed rotors and a gearbox, incorporated a squirrel-cage induction generator. The direct drive systems now coming into fashion employ multi-pole generators, with either wire stator windings or permanent magnets. Other System Components: Apart from the generator and related power electronics, the main markets for copper are found in transformers or inverters to change voltage from the relatively low voltage coming from the generator to that required for transport, and at some point an inverter changing delivery from DC to AC. Exactly where these components are found depends on system configuration, location (offshore or onshore) and size (wind farm or isolated). Cabling is a major element of the system also. A wind tower system with the transformer next to the generator will have MV power cables running from the top to the bottom of the tower, then to a collection point for a number of wind towers and on to the grid substation, or direct to the substation. The tower assembly will incorporate wire harnesses and control / signal cables, while LV power cable are required to power the working parts throughout the system. Figure 53: Cables Employed in an Onshore Wind Power System 
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