Supporting Africa’s Growing Power Needs: Investigating A Generator Failure
Any failure at a power plant is serious and can cause a loss of supply to a region or disruption to an associated industrial facility. In particular, generator repairs or replacement can take up to several months, resulting in a significant loss of income for the power station owner due to lost generation revenues.
Doble recently conducted an investigation into a generator failure at a power plant in central Africa. The plant operates twelve turbines running on natural gas which are coupled to 20.8 MVA generators. Originally built to meet peaks in local power demand, it is now in permanent operation to meet the country’s growing energy needs.
General View of the Plant
Maintenance activities provide clues
Maintenance had been carried out on regular basis on all the critical components of the plant, in particular, on the generator in the five years since commissioning. Maintenance operations in a generation group revealed visible evidence of partial discharge in numerous locations for the first time. The same issue was discovered in another group when a generator tripped on differential protection an hour after returning to service for Level 1 maintenance. This inevitably raised concerns of an issue affecting the entire family of generators at the plant.
Evidence of Partial Discharge
Partnering with Doble to identify the cause of failure
An expert team was assembled to inspect, test and diagnose all the generators at the plant with the aim of identifying the root cause of failure and to assess the condition and residual lifetime of the other generators. The team completed a thorough visual inspection of the failed generator and took samples for laboratory analysis.
One-by-one, outages were scheduled on all the other generators in the plant to carry out an in-depth visual inspection and to perform comprehensive electrical testing. Both online and offline electrical tests were performed including insulation resistance, polarization index, power factor, partial discharge measurements and EMI measurements.
The on-site inspection and electrical testing, combined with the off-site laboratory analysis, made it possible to identify the root cause of the failure of the first generator. It also provided knowledge to assess the condition of the other generators by focusing on the key areas of concern.
Changes to asset maintenance program to mitigate risk
As a result of the investigation, the power generation company decided to enhance its maintenance program with regular electrical testing and inspection. Newly-installed capacitive couplers on each generator regularly monitor partial discharge levels for changes and signs of developing problems. All of these changes help to mitigate the risk of another failure that could interrupt the fast-growing region’s power supply.
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