PROACTIVE SHOP STRATEGY FOR A SUCCESSFUL TURBINE-GENERATOR ROTOR OUTAGE

摘要

Standard power generation industry practices of inspection, machining, balancing, assembly and alignment have been developed and streamlined by OEMs for newly manufactured rotors, and implicitly assume that rotors are within ideal dimensional specifications. However, applying these standard practices in the service industry can fall short for rotors with eccentricities outside such specifications, and by design do not catch the errors that cause true dynamic problems, because they are assumed not to exist or their effects are fully unrecognized by "traditional industry practice" with regard to real rotordynamic behavior (not the rotordynamics theory based on a Jeffcot rotor). This misunderstanding leads to various problems, like reinstalling a "balanced" rotor from the shop only to be unable to run due to high vibrations upon installation. This can be followed by weeks of field balancing in an effort to salvage the situation. A "successful" start up following a planned outage means that there will be no need for field balancing following the restart of the unit. There are two key processes that must be incorporated into an outage scope to ensure success. The first is to collect and evaluate (1x and 2x) total indicator runout (TIR) readings to identify any excessive bow or distributed eccentricity in the rotor body between the journals, and to verify and machine all rotor couplings and journals to within the criteria of ISO 1940. Any excessive off-squareness of the coupling faces or any taper or runout of the journals must be corrected by machining. The second key process is utilizing a new balancing method if the rotor body exceeds runout limits of ~0.002" eccentricity. Any such bowed or eccentric rotor must be balanced in a minimum of 3 balancing planes (or more accurately, 2N+lplanes, where N is the highest mode reached by the rotor within its operating speed range). Since most causes of dynamic problems on turbine-generator rotors are present even prior to starting the unit, almost any such problem can also be identified and fully prevented ahead of time during an outage if only a few improved steps of measurement and analysis and the proper balancing method are included into an outage scope. By proactively incorporating rotor TIR evaluation, making provisions for any necessary machining, balancing any bowed or eccentric rotor in 2N+1 balancing planes, and following OEM alignment procedures, a successful restart of the unit without field balancing can be assured.