Compact frequency drives for four 250 tonne cranes

On the grounds of the Dutch Maasvlakte II port in Rotterdam, a new production facility has been built for the continuous production of seaworthy XXL foundations for offshore wind turbines and gas and oil platforms. These foundations, with diameters of nine meters or more, are hoisted aboard offshore ships directly from the assembly and coating facility. They are maneuvered using four special 250 tonne overhead cranes, produced by BKRS Crane Systems in Veghel, the Netherlands. Each crane has two Demag hoisting units, each with a nominal capacity of 125 tonnes.

In the hall measuring over 500 m long and 20 m high, the cranes, powered via a power supply rail, are controlled radiographically from the ground. The cranes are powered with 400 V three-phase 1200 A (maximum 830 KVe). The four separate 250 tonne cranes can be controlled independently but can also be linked, enabling one man to maneuver the extremely long loads of more than 1000 tonnes with precision using four cranes simultaneously. The two remaining cranes have the same construction as the other four cranes but are calibrated for 80 tonnes.

Due to the heavy loads, the customer requires high levels of quality of the construction of the cranes. The construction meets Execution Class 3 with annual inspection, which means that it has to satisfy the same requirements as, for example, submarines or nuclear installations.

For the exact command of these enormous loads during hoisting and transport, high demands are made on the motor control and crane process. BKRS Crane Systems has used Yaskawa frequency drives for many years already. The frequency drives from Yaskawa are perfect for heavy hoist-load control applications.

In this project, the new Matrix converter U1000 was chosen, characterized by its compact form and the absence of a DC bus. Thanks to the U1000 drives, highly efficient AC-AC direct conversion of the braking power to the mains net is possible. Due to this, the large amount of brake resistance normally necessary in order to process the braking energy is no longer needed. Due to special software installed in the drive, extremely precise control of the load is possible; during movement and braking the XXL load cannot be allowed to sway or rock, an important requirement from the customer.

The Matrix drives are the newest generation of regenerative frequency drives in the extensive range of drives from Yaskawa and fit perfectly into the ‘Green’ crane aspect that limits its CO2 emissions. Besides its compact form, it also has a high output and the standard U1000 satisfies the strictest international standards for the Power Factor. There is a global trend regarding the laws relating to harmonics and power factor; the Yaskawa U1000 already complies with IEEE519.