The energy company Grosskraftwerk Mannheim Aktiengesellschaft (GKM) runs one of the largest and most modern coal-fired power stations in Germany. After winning a major order for overhauling a spare rotor, Stork Technical Services (STS) carried out the work on an exceptional level – an achievement that no other European non-OEM can match.  

GKM's power station has a gross operating capacity of 1675 MW of which 1000 MW is produced as steam for heating. The power station supplies electricity to 1.5 million people and companies, and heating to 110,000 households. The overhaul of the 250,000 kVA rotor – that fits on three hydrogen-cooled rotary current generators – did not require working strictly against the clock because a suitable spare rotor was available. This enabled STS to make a successful bid for the order as a non-OEM despite not having the original documentation. STS presented better plans for redesigning the rotor and quoted a more competitive price than OEMs to win the order.

Multi-phase project
The overhaul was divided into a number of work phases. The original winding was removed first. This was followed by collecting data about the dismantled components and drawing up plans for redesigning the winding (taking account of and calculating the applicable ventilation principles). The two final stages of the order were the production phase and fitting the new rotor winding.

Dismantlement and tests
After removing the complete winding, STS engineers put the 40-tonne, 11-metre long, forged steel rotor shaft through an ultrasonic volume test and checked it for cracks using magnetic powder. STS immediately developed and implemented an overhaul plan to repair the cracks that were found.

Shaft modification
To ensure that the rotor would fit on all three generators, STS had to carry out a considerable amount of drilling, milling and turning work to modify the end of the shaft. Because the permitted tolerances were less than a few thousandths of a millimetre, this required extreme precision. After the modification phase, the rotor was centrifuged in a kinetic energy test tunnel at speeds up to 3600 rpm. GKM was extremely pleased with the test results.

Exceptional achievement
STS carried out the work outlined above that it was contracted to do as an independent service provider on an exceptionally high level. No other European non-OEM is capable of performing an achievement of this magnitude.