Rewind puts rotors back in service

Wyko has recently won a contract to overhaul nine 30MW turbo rotors following a successful proposal that included a bespoke insulation system and rebalancing.

Wyko has recently won a contract to overhaul nine 30MW turbo rotors following a successful proposal that included a bespoke insulation system and rebalancing.

The new insulation system used to rebuild the 15t rotors was specially designed and developed at Wyko to improve rotor performance and extend wear life in the power generation application.

Wyko was initially contacted by a UK client (who cannot be named for security reasons) to establish if effective repairs would be economically viable for a 30MW turbo rotor, which had failed in its duty of generating power from steam driven turbines.

An essential requirement for carrying out this repair was to demonstrate a cost effective and reliable insulation system that would also take into account the history of similar rotors at the client's establishment sharing the same design.

Turbo rotors are built by a number of manufacturers throughout the world and many have different design characteristics specific to the intended application and its environment.

However, one of the common reasons for reduced operational life is the fact that alternators are often relocated into an environment quite different from that which it was initially purchased for and installed.

Due to Wyko's knowledge of repairing many types of turbo rotors, its team picked up on the fact that they may have not been specifically designed for the application, and further investigation identified insufficient insulation for the application as one of the main reasons for failure.

Peter Ross, a Wyko Technical Director, was then able to put forward design improvements to the insulation systems that would meet all the operational and environmental requirements of the generation rooms at the client's installation.

The proposed new design included improved slot insulation and a new interturn design to improve thermal, mechanical and insulation characteristics.

Due to the original insulation having being physically worn, Wyko included the rebuilding and balancing of the giant rotors into the proposal in a way that offered better performance and more reliable operation.

The solution was far less susceptible to this type of failure and would not only be effective in the long term, but could also be economically applied to the eight units still in service.

After an extensive investigation by the client into evidence of Wyko's ability to carry out the repair work, the go ahead was given for the first repair and subsequent eight units pending successful installation and running tests.

Overhauling the 15t units involved complete disassembly, annealing, cleaning, nondestructive testing and condition reporting on every element of the coils.

To prepare the rotor body to accept the new rotor coils, it was cleaned and all insulation removed from within the slots.

Electrical tests were carried out to ensure integrity of the rotor laminations and a full mechanical datum check of the rotor body, rotor slots, rotor shaft and coupling also conducted.

Wyko's Newcastle upon Tyne workshop manufactured the specifically designed rotor slot insulations, which were supplied to the Wyko EMS Chesterfield for insertion into the rotor body, prior to the fitting of the rotor coils.

The rotor coils had also been insulated and had met the designated class H temperature classification (180C operating temperature).

Following completion of the rotor rewind and reassembly, electrical tests were carried out prior to stoving and curing of the rotor winding.

After the curing cycle, further electrical tests were then carried out before and during a 20% overspeed dynamic balancing operation.

As a result of the successful rewinding of this first turbo rotor, which met all the required design parameters and was in full operation, the client awarded Wyko the contract to rewind the remaining eight turbo rotors over a given period.

This is a typical example of the service available from Wyko EMS, which undertakes a number of turbo rotor repairs and large high voltage motor and generator repairs throughout the world, each with specific insulation designs intended for the particular operating conditions of the machines.

Back to top