Environmental Engineering Reference
In-Depth Information
turbine operating conditions, the main shaft must transfer the rotor plane bend-
ing moments into the tower supporting structure and ultimately into the founda-
tion (see Fig. 11). In addition, it must sustain transient and highly dynamic loads
caused by grid failure, over speed events, breaking, and emergency stops, as well
as loads due to extreme wind, gusting and environmental conditions.
The 10-turbine analysis group mass results for the main shaft and nominal bear-
ing arrangement are shown in Fig. 24. The main bearing trend is an average for a
single main bearing and a double main bearing type design. A single-bearing
design (e.g. GE1.5) uses one large bearing at the front of the shaft with the gearbox
and torque arms used to support the aft end of the shaft. A double-bearing design
(e.g. GE2.5) has a second independent bearing located at the aft end of the main
shaft and the main shaft supports the “fl oating” gearbox.
Figure 24 suggests a 10 MW main shaft to have a mass of nearly 55 tonnes and a
main shaft bearing or bearings of about half that amount or approximately 25 tonnes.
Using similar reasoning for technology advancement on the way to a 10 MW size
machine, it appears possible to achieve 37 and 18 tonnes for the main shaft and
bearings, respectively.
Based on the industry study set, the amount of steady-state torque being carried by
the main shaft to a generator or a combined gearbox
generator is shown in Fig. 25.
The effect of overall mechanical and electrical losses of 9 and 13% is included to
illustrate the effect on the steady-state main shaft torque. Assuming that the losses
for advancing technology while designing for a 10 MW machine are in the 8
−
9%
range, about 10,000 kNm of torque capability is needed at the rating point. This is
equivalent to about 16.2 Abrams M1A2 tank-meters of torque. Due to grid and
−
Figure 24: Main shaft and bearing mass from the 10-turbine analysis group.
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