Cruise Ship Generator Safely Repaired At Sea

Large civilian ships rely heavily on electrical power to provide passengers and crew with their daily comforts; such as lighting, communications, food, and entertainment. Recently constructed cruise ships also rely on electrical propulsive power, so the loss of generator power has the potential to cause concern on both accounts.

Having suffered a generator failure onboard a large cruise liner, an initial inspection by the ship’s maintenance engineering team determined that the 7.5MW generator had a winding fault which would require a complete strip-down and new windings to be manufactured and installed. The challenge was taken up by Sulzer, as the company has considerable expertise in completing high voltage generator repairs in-situ, as well as the facilities to design and manufacture new coils at very short notice.

The first step was to fly in a repair team who worked with the ship's engineers to dismantle the generator and determine the exact fault with the original windings. With space on a cruise ship at a premium, the engine room does not afford the same advantages of a purpose built workshop, but nevertheless the team soon had the rotor removed and safely secured.

A closer inspection of the stator revealed that the OEM design of the coils had a flaw and that had caused the generator to fail. Sulzer suggested a modification to the design to ensure that a similar failure would not reoccur and this was incorporated with the rest of the coil design details and sent to Sulzer’s Birmingham Service Centre in the UK, where the coil shop started work on manufacturing the new coils.

The challenge of electrical power onboard large cruise ships

Electrical power generation on large ships is achieved, in the main, by either large diesel motors or steam turbines turning generators, which provide the power for the entire ship. Due to the essential nature of these power plants, the installed capacity allows for some generators to be off-line, ready to be started in the event of a generator failure. They are usually separated from each other to ensure that any damage caused to one generator does not affect another.

Most modern cruise ships now employ some form of diesel electric power, where the diesel engines just power a generator and the electricity is used to power electric motors which are connected to the propellers or thrusters. The main advantage of this system is efficiency; the engines can operate at their optimum speed, regardless of the speed of the ship.

However, if a generator does fail, it is essential that it is repaired as quickly as possible so as to minimise the disruption to the passengers and crew and maintain the ideal level of redundancy within the system. In most cases this would require the vessel to dock in the nearest port with suitable repair facilities; however, Sulzer has the expertise to complete a full repair at sea.

Achieving a turnkey service at-sea

Mike Stanley, General Manager at Sulzer’s Birmingham Service Centre where the onsite repair teams are supported from, and the replacement HV coils are manufactured, comments:

"This project really needed a fast turn-around to ensure our engineers on the ship could get the generator back up and running as soon as possible. Fortunately, we are very well equipped to achieve tight deadlines with all of the processes involved, from 3D CAD designers to fix the original design fault, through to rolling the raw copper for the replacement coils in-house and the final high voltage testing, all carried out here in Birmingham.

"Once we understood the root cause of the failure we were able to modify the original design and start production immediately. This meant that while the new coils were being produced, the on-site engineers could finish stripping and cleaning the stator so that as soon as the new coils arrived they could be installed and connected."

With the new windings in place, they underwent a full series of tests to check the performance and the insulation resistance. Once complete, a temporary oven was created around the stator and the windings were cured, before the epoxy resin coating was applied and finally the windings were painted with a varnish based paint.

The team then reassembled the generator before testing, commissioning and finally returning it to normal service. The repair project was completed in 40 days, with two teams working round the clock on 12 hour shifts which ensured that there was no interruption to the ship's schedule, no inconvenience to the passengers and no additional costs for docking the vessel.

Mike Stanley concludes: "This is a service which requires us to be regularly certified by Lloyds Register and Bureau Veritas to ensure continued compliance with marine engineering standards. Our ability to complete these repairs while at sea provides a host of benefits to the passengers as well as the ship's owners.

"Our Birmingham coil shop can produce resin rich coils to precise specifications within very short lead times, which allows the ship to continue its journey. The alternative is to replace the generator or repair it as a global VPI (Vacuum Pressure Impregnation) winding, both of which would require a dry dock situation and a large hole being cut in the side of the ship to allow the generator to be removed. Our solution clearly offers a far more attractive alternative."