Viking Line and ABB have proven the concept of mooring winch upgrades, re-using old motors but updating to stepless speed control
During a 10-year collaboration between the two companies, a selection of mooring winches on three 30-year-old ferries were retrofitted with variable speed AC drives for stepless operation. Viking Line undertook the retrofit installations with ABB providing technical assistance and programming of parameters.
Older winches with electrical motors with three windings and direct on line (DOL) start have been a very well used solution in the maritime industry for around 15 years, says Mikael Holmberg, Sales manager for Marine Winches & Cranes at ABB, but a more robust and standardised concept with an induction motor and one winding is standard today. “The beauty of the retrofit is that the old motor, control stand and space in the electrical cabinet can be reused. No change is required to the winches on deck, which operators can use as before, but instead of DOL steps, now with quiet stepless speed control.”
For the retrofit, one of the motor’s windings is connected to the frequency converter via an output filter (du/dt) which protects the winding from variable speed drive voltage peaks. The winding’s nominal data is programmed in the frequency converter, and an identification run ensures compatibility.
The retrofit process enables upgrade to the company’s latest drive platform, ACS880, which uses a dedicated winch control program with inbuilt functionality for anchor mode, hand mooring, auto-mooring and clutch control (creep speed mode). All the features are programmable and adjustable by parameters available on the control panel on the drive or via laptop or smartphone.
The external circuit board used for tension control in automatic mooring mode in the old cabinet is replaced with inbuilt functionality in the frequency converter. All old joystick control signals are transferred directly to the frequency converter IO board, and the new functionality is enabled by the software without the need for load cell sensors, motor encoders and external programmable logic controllers.
The newly-available cabinet space in the electrical room is used to house the frequency converter, filter and other components such as the mechanical disk brake power circuit (usually 110VDC).
“Old external mooring controller hardware is therefore replaced with internal mooring software,” says Holmberg. “This can be important as old control board versions may not exist anymore. It also means there are fewer critical components, including relays and contacts, so maintenance requirements are less. And more information and functionality is available than before with the winch functionality software in the ACS880 drives.”
The resulting system can limit the available torque (Nm) depending on whether the winch is being operated in hand or auto-mooring mode. The motor’s mechanical brake is controlled via the frequency converter relay output and has inbuilt mechanical brake control to make sure that brake is fully open before the motor is rotated. In the stopping sequence, the motor speed is reduced to creep speed before the close command is given. Wear on components is therefore reduced, as the brake doesn’t have the stress of opening and closing at high speed.
“The speed controller must be tuned to ensure good speed control performance,” says Holmberg. “This require testings and real case experience. Now that we have completed several retrofits, we know the ‘rules’ and can adapt and use old motors with our frequency converters. These motors have no speed encoder feedback, and our new concept where no encoder is needed is now well used and working correctly after the identification sequence.”
The ACS880 control panel has digital displays for all signals including speed, torque and current. A load analyser monitors operational time and torque levels on the motors. Maintenance counters show parameters such as inlet temperature and control board temperature, and a fault/warning history logger stores historical information for fault analysis. The evaluation and programming of parameters can be done on the control panel via different menus or on a personal computer using ABB’s DriveComposer software.
ACS880 drives use an ABB memory stick to provide operational parameters to the control board. All software configurations set up for the drive are stored there, so if a drive change is needed, the memory stick can be taken out of the old drive and plugged in to the new one. “This is the most practical way of enabling drive functionality, as drive or spare part changes can be undertaken without the need for any programming skill,” says Holmberg.
Thousands of marine winches on all vessel types now have the potential for the benefits provided by upgrades similar to those undertaken on Viking Line’s ferries MS Mariella, MS Gabriella, and most recently MS Amorella, says Holmberg.