Up Time Magazine - December 2008/January 2009 - (Page 60) scheduled unit overhaul. While this was a very challenging case, not all machines are so difficult all the time. Rarely do so many problems exist at the same time on the same machine. Complex problems require complex problem solving. Each machine is different and that’s what makes this job so rewarding and keeps life so interesting. Greg Davison is the Supervisor of Reliability Technologies at Oklahoma Gas and Electric. He is an ISO Category III Vibration Analyst. He is a member of the Vibration Institute and the Oklahoma Predictive Maintenance User’s Group. Greg graduated from Oklahoma Christian University with a Bachelor of Science degree in Organizational Management. You can contact Greg at davisogd@oge.com Figure 9 – Shim pack used on right hand corner of the base plate. couple imbalance. Correcting the couple imbalance would require weights to be placed in both ends of the rotor. Even though this rotor had been balanced at the motor shop in a balancing machine, all symptoms suggested imbalance. Experience has shown that this is not uncommon in a vertical machine. In the balancing machine, the rotor is balanced when mounted horizontally. Then, when it’s turned upright to the vertical position, a couple imbalance is often observed. This, plus the fact that the motor is now sitting six feet above the floor on a base that allows much more movement, means much less force is needed to create unacceptable levels of vibration. Removing a cover allows easy access to the outboard end of the motor, where there are provisions for balance weights. However, access to the lower end of the motor is rather difficult. The only way to attach weights is to worm a hand and arm through and around to gain access to the cooling fan. Dispatch was now calling for load. Luckily, with historical balancing data in hand, one run was all that was needed to balance the rotor. The vibration was now at or below historical levels, so the motor was coupled to the pump. A performance test was conducted to evaluate the pump repair. This test proved the pump to be in good shape. Baseline vibration data was collected and the machine was returned to service (see figure 10). The unit was given back to Dispatch 29 days after the first problem was discovered. The old grouting was removed, the base was leveled, and new grout poured at the next Figure 10 - Twenty nine days after the original problem was detected, the repairs were complete and vibration levels at or below historical levels. 60 december/january 2009 http://www.sdtnorthamerica.com http://www.sdtnorthamerica.com
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