Page 208 - Fluid Power Engineering

180 Chapter Nine

FIGURE 9-9 Double
roller taper bearing.
1. Double rollers.
2. Taper. (With
permission from
SKF.)

turbine bearings (see Fig. 9-9) are a double row of tapered roller bear-
3
ings, with an outer diameter as large as 2.4 m. The trend is toward
replacing two bearings with a single large radius bearing and replac-
ing the bearing housing with a design that integrates the bearing into
nacelle frame.

Lifting/Lowering Mechanism
Vergnet’s 1-MW turbines have a unique mechanism to lower and raise
the upwind part of nacelle, including rotor blades and hub. The intent
is to: (a) reduce the cost of heavy cranes during erection and mainte-
nance, and (b) improve safety and reduce damage during a cyclone.
The Vergnet turbine has a split nacelle, a downwind part with the
auxiliary crane and generator, and an upwind part with the blades,
rotor hub, and gearbox. The tower components and downwind part
of nacelle are raised using a self-erecting system called VeriLift. After
the auxiliary crane is in place, it lifts the upwind part of the nacelle.
The lifting mechanism is shown in Fig. 9-10. More details are found
in Table 9-6.

Towers
Towers are tubular tapered steel structures. Steel plates of thickness
1
1
1 / 2 to / 2 in. thick are rolled into cylinders and seam is then longitudi-
nally welded. At the ends of the tower sections, flanges are welded to
the inside of the cylinders for onsite bolting during erection. Normally,
three tower sections are constructed and shipped to the site. There is
a logistical reason that limits the diameter of a tower. In the United
1
States, the minimum height of an overpass is 16 / 2 to 17 ft. This limits
the diameter of the bottom section of tower that can be transported
by truck to be less than 4.3 m. Rail transit has even more stringent