As part of the steel making process, the crane charges the plant’s three converters with molten iron from the blast furnace. To charge a converter the crane’s main hoist first lifts the ladle, which contains around 100t of molten iron. The crane is then positioned in front of the converter and the auxiliary hoist tips the ladle and pours the metal into the converter. Each converter is charged 25 times per day, with the plant operating on a 24/7 basis.
ABB industrial drives, along with ABB’s crane control programme, replaced the drives on both the main and auxiliary hoists. The existing drives – from another manufacturer – lacked master-follower functionality, spare parts were no longer available and there were no standby drives in the system for redundancy.
Master-follower
The main hoist is operated by four 110kW motors, two on each side of the drum. The existing drives were replaced with three 490kVA, 400V ABB industrial drives. Two drives are operated in a master-follower arrangement with a fibre optic link for load sharing.
The master drive operates in speed control mode and the follower in torque control. One drive is spare for redundancy should problems occur with either the master or follower drive. If a problem occurs, the spare drive can be connected using manual switches installed inside the drive cubicles to operate either as master or follower. In an emergency the main hoist can even be operated at lower speed using only two motors.
The auxiliary hoist, which is used to tip the ladle, is operated by one motor. The existing drive was replaced by two 130kVA industrial drives, of which one is used as a standby.
All the drives – both on the main and auxiliary hoist – feature inbuilt brake choppers and an external brake resistor.?
Speed control
The program utilises the drives’ direct torque control (DTC) technology to “deliver enhanced operational safety and accurate slow speed control with high torque levels,” says ABB.
ABB was chosen to perform the engineering, installation and commissioning work, and worked closely with the customer to configure the upgrade.
“This is a crucial production phase, where reliability is essential. We’ve been using ABB drives for many years and we know we can depend on them,” says Esa Prokkola, project manager at the Raahe works. “We were pleased with the way ABB worked to get the job completed during our plant shutdown, and since the upgrade everything has worked well with no problems. As a result we’ve asked ABB to upgrade our continuous casting crane.”
Ruukki Production’s Raahe steel works is the largest steel works in the Nordic countries. Steel slabs produced at Raahe are processed on site into hot rolled plates, sheets and coils.
