Propulsion problems resolved after demanding overhaul of 19 MW motor in just 26 days
A cruise liner operating with a reduced top speed can have difficulties keeping to its itinerary, so when one vessel had to cancel a destination, the owners needed the situation resolved quickly. Specialists from Sulzer have worked day and night to replace damaged coils in a 170-tonne (186-ton), 19 MW (25’500 hp) propulsion motor in an on board repair. Through the cooperation of several service centers the project was delivered on schedule, meeting the owners’ expectations.
Cruise liners offer holidaymakers a wide variety of relaxing experiences both on board and at many destinations around the world. Operators of these massive vessels depend of the huge propulsion motors to power them across the ocean, so a proactive maintenance program is essential to reliable performance.
Size is everything
High voltage electric motor experts from Sulzer in Australia successfully completed a demanding rewind project, replacing all the coils in a primary propulsion motor on one of the world’s largest cruise liners. The work was conducted entirely on board the vessel during wet dock, with engineers working on large components in very limited space and against a tight timescale.
The vessel’s owners called in specialists from Sulzer when one of the winding systems encountered a failure. It became apparent that the problem was extensive and complex, calling for a complete replacement of the stator coils. Fortunately, a dual-coil design made it possible to keep the motor running at a reduced duty cycle until a permanent repair was made. That would require the vessel to be taken out of service, and the owner decided that the work should take place during the next scheduled overhaul.
Planning constraints
Over the following months, Sulzer experts around the world collaborated to prepare for the rewind. The company’s specialist electromechanical repair facilities which also house a coil manufacturing shop in Birmingham, UK, accessed the specifications for the coils, so work could quickly begin on designing and manufacturing the critical components.
Meanwhile, experts from Sulzer in Australia conducted a series of inspections including a core test on the motor’s stator to ensure that it was in a suitable condition for rewinding. During the site inspections, significant time was spent on developing a detailed plan for the work. With limited space in the propulsion room, extremely careful sequencing would be required. The 16 rotor poles in the motor, each weighing more than 2 tonnes (2.2 tons), would need to be placed on the floor, which had been specially reinforced for the purpose. Ducting and walkways were removed to create sufficient room for the 100-tonne (110-ton) stator to be lifted 1’300 mm (51 inches) to allow access to the coils.
The Sulzer teams also had to manage complex logistics. The vessel’s overhaul was set to take place in a port in the Caribbean, and Sulzer would have a maximum of 26 days to complete the work. To prepare, the new windings were shipped from the UK to Sulzer’s environmentally controlled warehouse in Houston, while specialist tools and other materials were assembled in Australia and sent to a staging location in Fort Lauderdale, Florida.
Installed on schedule
16 Sulzer experts boarded the vessel on its arrival at the maintenance location. Over the next three weeks, the Sulzer team worked in shifts to dismantle the motor and replace the coils.
Operations had to be conducted with extreme care. The 2-meter (78 inch) long rotor poles, for example, had to be removed in a precise sequence to minimize rotor imbalance. Furthermore, the whole worksite had to be kept scrupulously clean to avoid the risk of damage to adjacent equipment.
Despite the difficult conditions, the Sulzer team worked around the clock, installing, taping, varnishing and painting the new windings and reassembling the motor in 26 days. As testament to the quality of their work, the motor required no additional balancing after assembly.
“Rewinding a 19 MW motor is a significant undertaking,” said Eumesh Jethwa, Works Manager at Sulzer’s Sydney Service Center. “Doing a job like this on board a vessel, and within such tight time constraints was a real challenge for our engineering team. The planning really paid off and the vessel’s owners have appreciated the benefits of the project, which ran like clockwork.”
