By Steve Blankinship,
Among maintenance outage quandaries power plant operators face is whether to send components off site for repair or have the work done on site. In instances where the job can be accomplished either way, some believe the choice is difficult. Even when logic dictates that work can be performed better in a fully equipped shop under a controlled environment, owners often have a “comfort” issue associated with letting an expensive piece of equipment leave their site and worry that a late return might lengthen the outage.
West Allis, Wis.-based ReGENco, which services steam turbine and gas turbine/generators, reports that about three-fourths of its business is done in the shop and one-fourth in the field. “If a job is a minor inspection or does not require major disassembly it would typically be performed in the field,” says James Folda, generation business segment manager. “Or if a component is very difficult to move out of a powerhouse, such as a generator stator, the work would typically be done in the powerhouse.”
Many components, such as generator rotors, are easy to move, and it makes sense to move those to the shop if major disassembly is involved such as taking retaining rings off or rewinding. As an added bonus, moving a component out of the powerhouse can relieve the shortage of laydown space typical of a major outage and provide better maintenance access to equipment remaining on site.
Folda believes there is a trend toward shorter outage durations, necessitating faster turnaround whether in the field or in the shop. There are also greater periods without major maintenance. “We used to see an annual minor outage and then a major outage at five-year intervals. Now it is typically seven to ten years and in some cases machines have not been apart in 15 years.” Such intervals between major outages means more damage to fix when an outage it finally taken. “We are also seeing more forced outages,” he says, “with attendant collateral damage. Being in the shop lets us deal better with additional problems we encounter.”
A recent job for a Southern utility demonstrated the advantages. The job included open, clean and close, generator rotor rewind, complete steam turbine seal replacement, LP blading repair and valve inspection. Scheduled outage duration was seven weeks. According to Dan Brandenburg, ReGENco project manager for the job, having immediate access to the engineering staff was a key element. “With the valves, we were able to take them apart, evaluate their condition and get started on the repairs for rapid turn-around time. The engineering staff was able to begin reverse engineering immediately and the manufacture of replacement parts could begin. Waiting for the part to be shipped from the field would have cost precious time.” The equipment was repaired, returned to the site and placed in service within the scheduled outage timeframe.
Owners sometimes think they are losing time in shipping components away when in reality, the larger, more accurate machine tools in a shop work faster. “Field tools are made to be portable, and as such are less rigid and it sometimes takes more time to get the job done,” says Folda.
High speed balancing, critical to fast field starts so necessary in today’s competitive power markets, is something that can only be done in the shop. “When a turbine or generator or rotor needs to be balanced, it makes sense to do it in our high-speed balance bunker located in our West Allis shop rather than trying to balance it on-site in the machine,” says Folda. High-speed balance guarantees smooth operation of the rotor at rated speed. Rotor vibration is observed through the entire speed range to overspeed, and balance weight planes across the rotor body are accessible. On generators, it allows for electrical testing at operating speed, therefore speed related electrical faults can be detected.
Today’s communication technology has gone a long way toward easing the anxiety pangs associated with equipment leaving the site. “We can allay those fears with project managers who act as a liaison between ReGENco and the customer from start to finish,” says Dion Bauer, turbine business unit segment manager. “The PM keeps the customer updated with reports and digital photographs taken regularly of the activities in the shop and e-mailed to customers so they see exactly what’s going on with their parts.”
Bauer says the ability to send digital photos back and forth has greatly facilitated both on-site and in-shop repairs. “That lets us get our arms around a situation with a few pictures. It allows us to share the information more effectively than ever before, especially when some owners have offices and engineers distributed around the country. We can get on a conference call with everybody looking at the same picture at the same time. We can also trade drawings digitally among a lot of people simultaneously. Of course, the customer is also welcome to visit our shop any time.”