POWER SUPPLY
Demag’s DC-Wind hoist in a nacelle.
types of lifting gear. The generators of wind turbines are sited at the top of tall towers – hard to reach in onshore installations, harder still in offshore ones. Yet they need servicing, spare parts and occasionally replacing. The hoist installed at the top of the tower, which raises and lowers the equipment, has become a design specialty of its own. The requirements for such a wind hoist are that it should fit inside the confined space of the nacelle (as well as being compact it will need to be of low headroom); that, though used (and maintained) infrequently, it should be reliable and always available; and that it must have long lift heights. The requirement can be up to 180m for onshore towers while the latest generation of offshore towers are getting on for twice as tall. Lifting speeds must be correspondingly
high. Thus, the 1,000kg-capacity GP W electric chain hoist from Swiss manufacturers GIS is specifically designed for wind turbines and has a lift speed of up to 16m/minute, but its lift height is up to an impressive 200m. Raising a load from ground level to the nacelle at that speed, therefore, takes 12 and a half minutes. This raises another problem: a load approaching the nacelle trapdoor at that speed is highly likely to collide with it and cause a potentially extremely serious and dangerous accident. Yet, to expect the operator in the
nacelle to stand at that open trapdoor and concentrate solely on the approaching load for ten tedious minutes or more without losing concentration is asking a lot – especially if he has to do it several times over in the course of the work. The GP W, therefore, switches from high to low lifting speed; the switching is automatic, actuated by a geared limit switch that comes into operation as the load approaches the top or bottom of the lift. Liftket has been producing wind turbine hoists since the earliest days of the sector in the mid-1980s. Their ‘plug and play’ hoists are designed for voltage levels from 110–690V for 50–60Hz, which can be used worldwide. One of their standard products is designed for a lifting height of 200m with a load capacity of 800kg and a lifting speed of 20m/minute, but capacities of several tonnes are also available. Liftket also make hoists for the offshore
sector, where the environment is much more severe. Towers are higher, winds are stronger and more continuous and, critically, threatened by highly-corrosive salt spray. Specifications, therefore, need to be much higher. Special corrosion protection and paints are needed, as are specialised materials. Liftket products can also be equipped with stainless steel chain and hooks to avoid corrosion, with some components made of aluminium rather than the plastic of the onshore versions.
Demag have their DC-Wind chain hoist, with capacities of up to 1,500kg and lift heights to 180m. Kito’s single-phase ED electric wind hoist is lightweight and robust as well as weatherproof and corrosion resistant. Load capacities are from 60–480kg or higher on request; Kito claim to be the only manufacturer to offer ‘electroless’ nickel-plated load chains. Electroless refers to a process of depositing the nickel by a chemical process rather than by electrolysis. The layer deposited is known for its hardness and for its uniformity. The advantages here are higher corrosion resistance – there is, for example, reduced hydrogen embrittlement, which is a known hazard of metals in marine environments – and lower wear compared with traditional load chains. Solar power also need not long detain us – it may well contribute very useful amounts of energy, but its lifting needs are fairly minimal and can be served by conventional non- specialised equipment. However, solar, wind and tidal energy all suffer from a disadvantage – their output is intermittent. Calm, windless days produce no wind power, cloudy days produce little solar, and that’s not to mention nights, which occupy on average 12 hours out of every 24, produce none at all. Renewables, therefore, have brought into
prominence another need – energy storage. The power produced at peak times must be
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