In the past, plants had dedicated personnel for different equipment, such as the generator. They knew their generator inside and out, and most likely they had been taking care of it since the plant was built and commissioned. Service providers, usually original equipment manufacturers (OEM), performed overhauls and presented test results to the plant operation staff. Often the final statement in the report was that the unit was okay to operate. It was then up to the customer to make a deeper analysis of the state of the equipment and decide on future service and upgrade needs.
Today, the plants often have less and less of their own in-house expertise on the equipment. At many of the older power plants still in operation there has also been a generational shift, with the older, experienced staff having been replaced by younger, less experienced employees who might also be tasked with a much wider area of responsibility.
The customers therefore need to rely more on the service providers’ analyses and recommendations. Service providers often still present results in terms of what they did and how at the outage, but the most significant question is not posed: why.
However, to keep the generator rotating, the operator needs to know the outage results that can help define specific maintenance and service requirements in the future. For this reason, we at Fortum eNext Turbine and Generator Services have developed a concept based on failure modes and how they can be diagnosed.
One key feature of a generator is that its performance does not deteriorate with time. It can be in place for a long time, working well, and then suddenly it doesn’t. Therefore, a generator overhaul is 10% about reconditioning (such as cleaning, changing gaskets, slot wedge re-tightening and grinding slip rings) and 90% about diagnostics. This means that performing the right diagnostic tests and analysing the results becomes crucial.
Based on our experience in servicing rotating equipment, we have concluded that there are approximately 100 failure modes that can cause a forced outage of a generator. An analysis has been conducted at the component level, detailing all the potential failure modes that can occur. The ones of interest are those that have the potential to cause an unplanned outage. By analysing the failure modes, we have been able to define which diagnostic tests can identify each of them.
An important aspect of successful diagnostics is the test methods used. At the core of the Fortum eNext concept is the ability to detect failure modes at different inspection levels. As expected, a major overhaul is clearly the most powerful tool and the most important way of detecting and identifying failure modes. The second most powerful detection tool is on-line diagnostics.
When Fortum eNext performs a diagnostics assignment, the inspections and diagnostic tests are analysed by experts who have advanced generator expertise, and a four-level risk assessment is made for each component. Level 1 indicates a base risk, while level 4 indicates a high risk. The risk level of the generator is equal to the highest component risk. Recommendations are always given on how to reduce the risk of a forced outage and its consequences.
The Fortum eNext diagnostics service and resulting analysis report give plant owners a solid basis for updating their maintenance plans and serve as a guideline for future investments, in order to keep risks at an acceptable level.
We call it generating peace of mind.