Control Techniques Drive Centre, the Netherlands has recently completed the retrofitting of four floating grab cranes. All four cranes, situated at Amsterdam, have the four-rope grab system and are mainly used for ship to quay bulk handling. Two of the cranes are rated at 16-tonnes and have been retrofitted with AC Unidrive variable speed drives, while the two larger 25-tonne cranes have a DC solution, with Mentor II DC drives.
The 16-tonnes floating grab crane, built by Figee, is a Lemniscate type and mounted on a barge. For the different movements standard AC-motors were used. The AC-motors for the hoist and close movement of the grab, as well as the motors for the luffing and slewing movement, are all equipped with Unidrive AC drives.
The data communication between the Unidrives in the control room is based on our high speed network, CTNet.
Control Techniques provided a turn-key service, including design, engineering, software and programming, the building of the panels and the final installation and on-site commissioning at IGMA Amsterdam.
The scheme comprised Unidrive AC drives on a DC-Bus system, with CTNet-communication between the grab hoist and the grab close drives.
Squirrel cage AC motors controlled the movements of the hoist/grab closing (2x160kW) driven by 2 double size 5 Unidrives, both the luffing (1x40kW) and the slewing (2x 39kW) are driven by a 55 kW Unidrive each. The configuration is a standard drive system with a single quadrant rectifier and brake choppers. Since the crane is powered by a diesel engine/ generator set, energy stored in the system cannot be regenerated as with many other dockside cranes. A diode bridge rectifier supplies the inverters for hoist, slewing and luffing via a common DC-bus giving high reliability. Large brake choppers are required to convert potential energy stored in the hoisting system, or kinetic energy stored in the moving masses, into heat, since no regeneration into the grid can take place. The brake resistors are mounted outside the control panel. The crane control system requirements include slewing control, grab hoisting and closing and load dependent speed control on the hoist movement. All this software functionality was achieved without a PLC, using the integrated software solution inside a plug-in programmable application module built-in to the drive.
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