Sixteen bright orange-coloured Liebherr tower cranes soar in the sky above Dubai. They are all contributing to the completion of the Jumeirah Beach residence project. The four hotels and beach clubs will house 25,000 people in their 36 towers. Both cranes with the humble name "112 HC-L" are of particular interest. They have been custom-built for this job, and carry loads exclusively by raising and lowering their crane arm (jib) which soars high into the sky. They are luffing jib cranes and sit on self-built towers. In Dubai, they have a hook height which reaches up to 240 metres with a 12,000 kg maximum load.
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Weidmüller is on the scene when the cranes are operating – around the globe
The Litronic tower cranes are completely controlled by a PLC controller from ABB. This controller uses relays from Weidmüller's MICROSERIES. They are only 6.1mm in width and need very little space on the mounting rail. The MICROSERIES is perfect for use between controllers and actuators, for switching small to mid-sized loads. Level conversions and switching amplifiers can also be easily implemented.
The power supply for the crane can also be fitted with surge protection if the customer so desires. Weidmüller delivers turnkey die-cast aluminium housings completely assembled and ready for connection. The housings feature combi arresters for surge protection and also application-dependent NH back-up fuses. This enables the discharge of lightning currents up to 35kA and 10/350 μs for each conductor.
QUESTIONS for Bruno Ernle, Team Leader of Control Systems for top-slewing cranes at Liebherr
Why do cranes sometimes topple over?
Ernle: Properly erected and well-maintained cranes do not topple over. Such events are prevented by mechanical and electronic overload protection systems. If such an unfortunate incident does occur, then it is only because the safety settings have been manipulated.
How often are cranes struck by lightning?
Ernle: Less often than people imagine it happens because of their height. Our cranes are well grounded and can be ordered with lightning and overprotection modules for regions where lightning often strikes. Combination lightning arresters, such as those offered by Weidmüller, offer total protection against lightning strikes and overvoltage occurences. The combination can discharge lightning impulses with up to 35 kA and 10/350 μs per conductor.
Do you also have a crane that dismantles cranes?
Ernle: Yes – we call him Derrick. Derrick is the name given to a crane that is used to ramp up pylon constructions. We use it to dismantle our big jib cranes, for example those used in the construction of high-rise buildings and grow in height together with the building. The derrick itself can be dismantled with extremely small hoisting tackle and taken down the lift for transporting away from the site.
