Examining the Windformer -- ABB innovations

Nine months ago power giant ABB announced it was entering the wind business with major new innovative technology. Getting to the bottom of exactly what innovation ABB is offering in combining its Windformer concept with its High Voltage Direct Current (HVDC) Light cable technology has had the wind industry speculating ever since. Detailed information is scarce and the company's claims of reduced losses and cheaper power, achieved through a 50% cut in O&M costs and a 20% increase in energy production, are difficult to substantiate without hard facts.

In brief the Windformer, an adaptation of ABB's "powerformer" technology, combines several features to enable delivery of high quality power to the grid, with reduced system losses, by a wind turbine with fewer components than normal. It is perhaps the combination of several innovative or unusual features which makes Windformer different, rather than most of the features themselves. In addition, HVDC Light, by enabling the transmission of DC power at lower cost than standard HVDC cabling (Windpower Monthly, December 1988) is an essential element of the ABB concept if it is to be cost effective.

So what innovations does Windformer possess? First, the direct drive generator obviates the need for a gear box, as with the Enercon range. Second, the use for the first time at this megawatt size of a permanent magnet rotor for the generator does away with the need to use an electric current to induce the necessary magnetism. The efficiency advantage is small, but results in simpler construction.

Third, the stator -- the fixed outer assembly (the "collar" on the Enercon turbines) in which the power is generated -- is wound with round cables instead of the more square insulated copper conductors usually used. In this way losses in the windings, which typically make up 4% of all electric losses in a generator, can be reduced by 25%, bringing total losses down to 3%, a small but useful bonus to generator efficiency, though at the cost of special cabling. Fourth, the efficiency of the generator is further improved because the rotor, not carrying an electrical current, needs no cooling. The efficiency gain is probably another 1% to 1.5%.

Fifth, the Windformer's power electronics will condition variable speed turbine output to grid quality power and indirectly regulate the speed of the rotor so as to optimise energy production. Sixth, the output power will be gradually reduced as the wind speed rises above 18 m/s until it reaches 27 m/s. This avoids sudden losses of output when the cut-out wind speed is reached.

Seventh, the output voltage from the generator discussed to date by ABB will be around 25 kV DC, a level suitable for marshalling the power in a wind farm. Most wind turbines today generate at 400-750 V AC, with their voltage being raised to 11-36 kV by transformers in or near the tower base. The need for these is eliminated with the ABB system, though an inverter.

ABB claims the system is ideal for offshore wind farms. There is an ongoing debate about the economic merits of using DC transmission at significant distances from the shore. If DC is used with "conventional" wind turbines, rectifiers are needed at the wind farm, but turbines with the ABB system do not need these. The system would therefore come into its own with wind farms tens of kilometres from the shore. Perhaps more importantly, the company claims its combination of innovations means the unit as a whole will need less maintenance and have a higher reliability.

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