here in South Africa,” he says. “The
imported components are typically
laid down and stored in the port until
the site is ready to receive these
components. Once the wind farm site
is ready, these components are loaded
onto abnormal load vehicles at the port
for road transport to site. Upon arrival
at site, the components are offloaded
on the individual WGT crane pads for
installation; this is done using the 750t
LG 1750 as the main crane.”
The weight of the tower sections
varies and could be up to 81t per
section. Two cranes are required to
lift the sections from a horizontal to a
vertical position. The main crane then
holds the section in place while it is
being bolted to the foundation or lower
section. The componentry for the power
generating function of the turbine also
comprise substantial weights.
“With the tower in place, the
lifting and placement of the nacelle
with generator, drive train and
gearbox installed – weighing up to
97t – follows. In some instances,
the generator, gearbox and drivetrain
are installed separately due to the
excessive heights at which these
components need to be installed,” he
says. “The rotor consisting of the hub
and blades completes the mechanical
installation. The hub itself could weigh
up to 30t while each of the three
blades could be as much as 15t.”
Grotius says two very different
concepts are being used when it
comes to the installation of the rotor
and Johnson Renew’s lifting expertise
covers both installation concepts.
Some OEMs require the hub and
blades to be assembled on the
ground and lifted as a unit which is
then attached at height to the nacelle.
Others require the installation of the
hub as a single unit with the blades
installed separately at height.
“Each option has its own
complexities,” says Grotius. “For
www.equipmentandhire.co.za
installing blades separately, for
instance, a special tool is required to
clamp the blade when lifting so it can
be aligned to the hub and secured.”
To lift and install an assembled
rotor, on the other hand, there is the
combined 75t weight to consider as
well as the length of the individual
blades that could be as much as 67
metres. This assembly needs to be
lifted from a horizontal position using
two cranes, and carefully manoeuvred
using guy-lines from the ground to
keep the blades clear of the boom
of the crane and the installed tower
sections and to align it for final
installation.
“Designed with large surface
areas relative to their weight, the
blades can be quite tricky to lift and
place, especially as there are usually
intermittent periods of sufficiently low
wind speeds during which these lifts
can be carried out,” he says. “Success
is all about the engineering and planning
of these lifts. We select cranes of
optimal capacity, and apply the highest
levels of experience and expertise, from
computer modellers through to crane
operators to ensure the safest possible
execution of these lifts.”
It is also vital to calculate in advance
the maximum wind speed that the lift
can accommodate, and then to monitor
the wind on site closely to ensure
that work is conducted within the
prescribed limits.
“The challenge is obviously the
pressure of keeping to the project
schedule, which usually requires
installing up to two turbines a week,”
says Grotius. “We therefore have to
be flexible with regard to the timing of
the lifts and the affect this has on our
working hours. If the wind speeds are
too high during the day, we may have
to work through the night when the
wind speed drops to acceptable levels
for safe lifting and by doing this we
keep the project on track.”
Renew
PRODUCT FOCUS
Installation underway at a wind farm
using a 1 200t hydraulic crawler crane in
combination with a 100t crane.
LIEBHERR LG 1750
Among Johnson Renew’s fleet of mobile
cranes – the largest in Africa – are three
specialised 750t Liebherr LG 1750 lattice
boom mobile cranes, ideal for wind farm
work. Mounted on a wheeled carrier, these
mobile cranes can move along a standard
road between wind turbines. This eliminates
the need to construct excessively wide and
expensive roads that are required for the
large crawler cranes. The LG 1750 can also
rapidly relocate between installation pads,
saving time and costs and adding value to
the project.
AUGUST 2019
21