TOWERS: TYPES, FUNCTION, METERIAL REQUIREMENT, METERIAL JUSTIFICATION.

Tower are the supporting structure for wind mill which carry load generated from turbine. There are different types of wind mill towers, some are 1. Lattice tower 2. Tubular tower, 3.Hybrid towers. Pitchers are shown below.

1. Lattice tower 2. Tubular towers 3. Hybrid towers As the cost of the tower is a significant portion of the overall wind turbine systemCost, they are often optimized in order to minimize the cost of the tower.

1. Lattice towerThe lattice tower is made from trusses or frames that are bolted or welded together asShown in Figure.The initial cost to build a lattice tower is less thanThe tubular tower because it requires less material for similar stiffness.The assembly and maintenance Costs may be higher as each bolt needs to be torqued to a specification and checked periodically.

2. Tubular towersThe tubular tower is shown in Figure.It has a pipe cross-section. Many tubularTowers are either tapered (conical) or stepped which has increasing diameter towards the bottom. In addition, for stepped tubular towers, the thickness of the wall canBe varied along the height of the tower in order to save the material while satisfying the structural requirements.Although the initial material cost may be higher than theLattice tower, it does not rely on many bolted-connections which need to be torqued and checked periodically.

3. Hybrid towerThe hybrid tower combines different configurations of the wind turbine tower. The hybrid tower shown in Figure.It is called stayed design which combines steel tube, steel truss and guy-wire.The tubular type has a major section size limitation of about 4.3 m for larger turbines. This limit may result in site welding and fabrication which may compromise the quality of the tower.

PROPERTIES REQUIRED FOR TOWERS

The towers are required to be strong enough to support the weight of the blades and generator/nacelles.

They must also withstand fluctuating wind loading and loading resulting from turbine blade rotation.

This means that the towers must be stiff and strong. They do not need to be particularly light if positioned on-shore, although all foundations will be cheaper if the overall turbine weight is low.

Transport to location is an issue and it will help if the tower can be made from sections and assembled to ease transport issues. Again weight will be an issue but it is secondary to other considerations.

If a turbine is placed off-shore, then the weight becomes of greater importance in terms of the costs of foundations and the cranes necessary to install the turbine.

Corrosion is an issue particularly off-shore.

Materials for Wind Turbine Tower

The two most common materials used for wind turbine towers are structural steel and reinforced concrete. It is more standard to use steel. Steel is also galvanized or painted to protect it from environmental damage such as corrosion.

Composition and cut view of tower is as shown in figure for an small height wind mills.