Topic 2-Indirect Drivetrain‐Gearbox Design

Question 1

What are the key mechanical components in the conventional drivetrain of a wind turbine?

Answer 1

The gearbox, main shaft, couplings and mechanical brakes.

Question 2

What are the most important considerations in designing a wind turbine gearbox?

Answer 2

: The speed up ratio between the rotor shaft and generation rotating shaft; number of gear
stages required; gearbox loads, dynamic characteristics, weight and cost.

Question 3

For a gearbox design using two planetary gear stages, determine the number of gear teeth if the overall ratio of the gearbox is approximately 35.8. In selecting the gears, a number of teeth between 21 and 115 may be used. The maximum ratio for each planetary gear stage is assumed to be 7:1. Gear diameters should meet the geometrical relation of a planetary gear stage.

Answer 3

For 1st stage: 111, 46, 19 give 1+111/19=6.842, the numbers of teeth satisfy NR=2xNP+NS.
For 2nd stage: 89, 34, 21 give 1+89/21=5.238, the numbers of teeth satisfy NR=2xNP+NS.
The overall ratio: 6.842x5.238=35.838.

Question 4

Using the gearbox designed in Example 2, if a generator of 4 poles is connected to an electrical grid of 50 Hz, what is the rated rotor speed when the generator rotates at its synchronous speed?

Answer 4

As the overall gearbox ratio=116.24; the generator has 4 poles, thus the synchronous
generator speed nsyn = 60x50/(4/2) = 1500 rpm.
The rated rotor speed =1500/116.24=12.9 rpm.

Question 5

: Using the gearbox designed in Example 1, if the rated rotor speed is 14.24 rpm, what is the synchronous speed of the generator?

Answer 5

The overall gearbox ratio=35.1; the synchronous generator speed=14.24x35.1=500 rpm.