Rewinding… Maintenance Partners knows all about it. Every year, at least 100 electrical machines are rewound in Maintenance Partners’ workshops. It is safe to say that MP’s rewinders excel in their profession. Perhaps for that reason, the team was asked to perform a very special task.
MP was selected to rewind a high voltage generator in the engine room of a ship: a unique project.
The ship is an offshore supply ship that is used to support offshore oil platforms and the installation of wind turbines at sea.
A generator manufacturer (OEM) contacted Maintenance Partners in August 2018 about the repair of a 5134 kVA generator with a voltage of 6600 volts and a speed of 720 rpm at 60 Hertz. This generator is one of three identical generators aboard that provide the ship with electricity. The generator had failed and the other two weren’t in perfect condition either. Because of this, the ship could not operate at full capacity.
The generator’s problems were caused by the use of magnetic wedges that keep the windings in the slots. This type of wedge is mechanically weak and degrades over time. One of the degraded locking wedges had come loose and was dragged along by the rotor which damaged the insulation of the winding as a result.
In-situ rewinding aboard a ship is very different from rewinding in the workshop. The fact that the engine rooms of this type of ship are crammed with machines and equipment causes the generator to be fixed in its position. Moving the ship to a dry dock and removing a part of the hull was not an option for the customer as the ship could not be taken out of service for a long period of time. In this case, the shipping company choose to repair the generator aboard, even if in difficult circumstances. Before the works could begin, the rotor had to be removed. But there was not enough space so a couple of pumps had to be removed and a hole was cut in one of the sidewalls.
The team then proceeded to inspect the generator with a borescope. During the inspection, the stator core was also checked for short circuits. The stator core turned out the be in good condition so the rewinding could proceed.
For projects like these, a highly detailed preparation is crucial. Not a single item can be forgotten as missing tools and equipment are disastrous for the completion of the job.
These generators are constructed with a soft coil system and are entirely impregnated under vacuum. A soft coil system under VPI is difficult to remove.
Re-engineering to resin rich coils
The removal of the coils took the most time. The new windings can not be treated in the same way as there is no vacuum impregnation tank available. To overcome this, the customer agreed to modify the soft coil system to resin rich hard coils. The resin rich system is an older design than the soft coil system, but equals its modern counterpart in quality. The reverse engineering of the coils was performed inhouse by Maintenance Partners. After the rewinding, the customer and a classification society had to approve the repair as original manufacturer to allow the ship to be insured again.
Result for the customer: “a piece of art”
Thanks to the in-situ rewinding aboard the ship, a repair in the dry dock could be avoided and the ship could return to service in a shorter time.
The successful result of this intervention allows Maintenance Partners to show its expertise and eagerness to step out of its comfort zone. The customer called the result ‘’a piece of art’’.
For more information about in-situ rewinding of generators, call us at +32(0)35417140 or send us a message using the form below: