Article Ref – ART206
The photo shows one of the Mars Stator Casings removed from the turbine. It is removed for trim balancing and when aggressive cleaning of the rotor and stator blades and vanes is necessary.
A common issue with Solar turbines is locking of the guide vanes. Service Bulletin 8.6/107 was issued on this topic. Plus a general bulletin 8.6/112 was issued giving guidance on maintenance in general, plus for long periods of stand by.
On the Mars the variable vanes are the first six stages of compression. They are mounted and change angle on an inner and outer bushing. Dirt and corrosion builds up in the bushing clearance causing the the guide vanes to bind or lock up. This problem can be further complicated when operating in salty atmospheres such as off shore platforms.
There is logic used with the PECC actuator during the purge crank, to cycle the IGV and check the force needed to move the IGV. If there is excessive force needed then an alarm will be issued and a start will prohibited. Older units may not have this logic, but it may be available as an upgrade.
There are two positions for adding weight to the Mars rotor, the forward rotor hub and at the compressor eight stage. The compressor half case (in the photo) has to be removed to add or modify the trim balance weight. Solar Engineering know what the influence coefficients are for the Mars rotor. This means that Solar Engineering know what result to expect, by adding or removing weight at at either location. This means that you would probably only need to make one trim balance adjustment. It would be worth contacting them for this information if you were going to do the trim balance yourself for the first time.