Green Collar Careers - Wind
Turbine System Overview
|Nacelle is the
official wind industry term for the unit containing:
- Turbine Blade Hub & Bearings
- Gearbox (if equipped)
A gear reduction and direct drive (gearless)
units are shown to the right. Currently gear reduction
units are selling at lower cost although that will soon change as
the direct drive units cost less to produce. Direct
drive units usually include the inverter unit as an integral
component of the nacelle. Most wind turbines require a form
of braking or retarding when high wind conditions persist.
Some direct drive systems will use the inverter to retard the
turbine speed which is the most efficient way to control overspeed
Click picture to expand
Gearboxes are generally lubricated with grease to simplify sealing
and minimize leakage. Grease tends to thicken in lower
temperatures and adds a significant drag below about 20° F.
Where oil may be used in some gearboxes seals are crucial to maintain.
Grease will tend to last longer between changes where oil will need to
be changed periodically.
Direct drive has no gearbox and the only lubricated parts are the
sealed bearings. These will generally last 20 years.
systems are almost always a brush type generator. Brushes are a
wear component adding to service requirements.
AC output systems use
alternators and don't require brushes. Inductively coupled
alternators require a circuit that controls excitation voltage; this
circuit may be integrated into an inverter which will be mounted
inside the nacelle. Inductively coupled alternators will require
a gearbox with at least a 10:1 ratio.
Permanent Magnet alternators can operate at direct drive speeds.
Inverters with an integrated control circuit will be installed in the
|As the wind direction
changes the nacelle will need to rotate to point the turbine
blades into the wind. Directional changes are known as
"yaw". Most nacelles have a rotary yaw table on the bottom
side for mounting to the tower. Nacelle units equipped with
a tail fin position the unit so the wind strikes the blades and
the tower is downstream (leading), where units without a fin
position the blades downstream of the tower pole (trailing).
Both leading and trailing flows have their benefits.
Towers come in a variety of styles and heights.
- Monopole towers have the least maintenance
and highest price
- Guy Wire poles are the least expensive and
the highest maintenance
- Telescoping poles are the easiest to erect
and some allow easy nacelle access
Heights range from 20 - 100 feet.