Once considered a symbol of environmental fanatics, wind turbines are becoming a common sight through industrialized countries. Most consist of a tower with a generator mounted on top and driven by a single, multi-bladed turbine.

A big advantage to the Optiwind generator is that it can be assembled on the ground, then simply tilted upward, eliminating the need for cranes and expensive installation. Erection is accomplished using a pair of hydraulic cylinders powered and controlled by a HPU designed and built by Advance Motion Control.

Optiwind, of Torrington, Conn. has a different idea. They place a large cylinder shape atop a tower to divert and accelerate wind through a series of repositionable turbines, which capture energy from the wind and transmit it to a generator. The cylinder is said to produce a venturi effect to capture more wind energy than a conventional design of equivalent size does.

The tower of the Optiwind design consists of a central lattice structure reinforced by a triangular mounting. One advantage to this design is simplicity of erection. Instead of having to use tall cranes to erect the unit upright in place, it is erected in one piece from horizontal to vertical using two of its triangular points as pivots. This is where hydraulics comes in.

A tall order for hydraulics

The tower is pivoted upright by a pair of double-acting hydraulic cylinders, each with a 13-in. bore, 195-in. stroke, and 9-in. diameter rod. They are supplied by a hydraulic power unit (HPU) designed and built by Advance Motion Control, a Div. of Devine Hydraulics, Oakdale, Conn. The cap ends of the cylinders are secured to a separate foundation, and they produce a total of 440 tons of force to swing the tower upright.

Craig Goodsell, applications manager for AMC, saw the greatest challenge as maintaining consistent speed of piston rod motion during all stages of raising and lowering the tower, despite changing loads. For example, maximum force is needed at the beginning of the lift, when the tower is nearly horizontal. As the tower is pivoted upward to a steeper angle, load decreases, and actually becomes an over-running load once the tower is pivoted beyond an angle of about 84° to 85° At this point, pressure must be greater in the rod end of the cylinder than in the cap end to keep the tower from tipping forward.

Power and control
Hydraulic power and control are accommodated using a load-sensing axial-piston pump and proportional directional control valve from Sauer Danfoss. This combination maintains consistent speed control despite the changing load. The pump is driven by a 39-hp diesel engine, but Goodsell says the HPU uses only about half of that. To suit this application, the proportional valves feature pulse-width modulation (PWM) and ratiometric control. PWM takes the valve straight open, and the ratiometric feature divides the 12-Vdc supply signal in half — 6- to12-V to control one direction, and 1- to 6-V to control the other.

Diesel-driven hydraulic power unit uses proportional directional valve and flow divider to control and synchronize a pair of hydraulic cylinders to erect Optiwind’s generator.

To ensure that motion of both cylinders is synchronized, Goodsell also specified a cartridge-style flow divider from Sun Hydraulics. The pressure-compensated flow divider ensures that equal flow is routed to both cylinders. The HPU delivers a maximum flow of 7 gpm at pressures to 3650 psi during extension (240 tons/cylinder), and 4350 psi (150 tons/cylinder) during retraction.

An integrated radio transmitter and receiver control unit allows the operator to stand in the most advantageous position during tower erection. A transmission handset incorporates a progressive trigger that is programmed to vary the speed of the cylinders’ piston rods from1 to 7 in./min.

The HPU also has an emergency power feature. If the diesel engine should stall or fail, a hand pump can be used to position the tower to a stable position. If the tower angle has not yet reached roughly the 84.5° position, pressure from the hand pump can control counterbalance valves to allow controlled lowering of the tower back to the ground. If the tower angle exceeds about 84.5°, the counterbalance valves can be used to delicately allow gravity to pull the tower to a full upright position.

For more information, call Advance Motion Control at (800) 922-4154 or visit www.dhict.com. To view a video of the Optiwind energy converter, visit www.optiwind.com/video.html.