21345kVA AC Generator Exciter Replacement

ABOUT:

Founded in 2005, Contour Global provide wholesale power generation, currently generating approximately 4.1 gigawatts, utilizing 69 power plants in 19 different countries across 3 continents. They operate thermal energy plants using gas, coal and oil (63%), as well as renewables such as hydro, solar, wind and biogas (37%) and focus on unserved markets for energy supply.

CHALLENGES/PROBLEMS/REASON FOR PROJECT:

PPI were requested to visit Contour Global SA in Lomé, Togo to replace the exciter armature and stator on a 21345kVA AC generator which had failed in service. The customer needed the generator up and running as soon as possible to enable them to maintain their energy output levels. As a developing country Togo has traditionally purchased energy at great expense from neighbouring Ghana and Nigeria, so it was critical to have the generator up and running quickly to reduce costs. PPI had visited previously on a number of occasions to carry out repairs and modifications to the generators on site there.

WHERE DID PPI COME IN:

Our engineer arrived in early February to fit the spare exciter that the customer had in storage. This involved dismantling the machine to gain access to the internals, removing the old exciter armature and stator, fitting the new parts, resetting the airgaps, electrical checks, re-assembly and re-checking the machine alignment. Our engineer was assisted by local labour in challenging conditions, working in high temperatures in high humidity. The work took a little over a week to complete after which the machine was run successfully.

RESULTS:

The customer had concerns about the other machines on site as the problem had occurred on more than one occasion. PPI concluded that the failure was a result of high levels of ambient vibration coupled with operating temperatures causing fractures in the tape holding the stator coils in position. PPI sourced replacement equipment for the customer with a modification to the original design to arrive at a better solution for the retention of the coils to prevent future failures, and suggested appropriate maintenance protocols to be undertaken on the existing equipment to monitor condition and maintain operation.

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