Predictive maintenance and condition monitoring technologies are now widely accepted in power generating stations. There is little doubt that vibration information is the single best indicator of the general condition of rotating and reciprocating equipment. Normally, we select machinery to be monitored on the basis of equipment costs, maintenance costs, expected reliability, and the impact of failure. However, in a power plant just about every piece of rotating machinery is vital to maintaining optimum power output and efficiency, so it is conceivable that vibration analysis could be applied station-wide.

Assisted by vibration analysis, predictive maintenance and condition monitoring programs help avoid plant downtime or reduced output. For example, just a 6 percent reduction in power output in one large generating unit costs over $200 an hour.

Another unit, a 1,140 megawatt generator, produces electricity worth $21,000 per hour. Reduced power output due to downtime or less efficient operation impacts a utility's customers; in the new climate of deregulation this conceivably leads to a loss of business.

Maintenance people at power plants should look at potential suppliers of predictive maintenance and conditioning monitoring services who are capable of corrective measures in addition to analyzing vibration data. Corrective actions include laser alignment, precision balancing, root cause analysis, and other vibration reduction techniques. Effective vibration analysts should have a minimum of three years of on-the-job experience, formal training, and self-learning for paramount effectiveness; obviously, additional experience is a bonus.
 

A vibration analysis program that identifies equipment problems but does not address them and correct them cannot and should not be cost justified.The vibration analysis program can be maintained within the power plant employment structure or contracted from a specialty firm.

Expectations
The fundamental expectations of an effective vibration analysis program are increased equipment availability, therefore increased power production and reduced operating costs. An effective vibration analysis program helps maintenance do more cost-effective work. To enhance equipment reliability, the vibration analysis program identifies and resolves equipment problems. Typical problems that can be detected and corrected with an efficient vibration analysis program include misalignment, imbalance, resonance, mechanical looseness, bad bearings, pump flow problems, gear anomalies, electrical problems associated with motors, and belt drive problems.

In addition to addressing problem equipment, monthly vibration data collection and analysis allow maintenance people to tend to problems as they arise. This permits trends in equipment problems to become clear with time and to be resolved before they become maintenance and reliability issues. These repairs work can then be scheduled in order to ensure reliability. Spare parts inventory may also be optimized. Regularly scheduled preventive maintenance work can often be deferred, which also saves money. In fact, one of the objectives of predictive maintenance and condition monitoring is to do maintenance only when necessary, thereby increasing equipment availability.

The following example illustrates the effectiveness of vibration analysis. It is imperative that the vibration signals are analyzed correctly to implement necessary corrective actions successfully.

We have chosen the ball bearings on a Hoffman blower as an example. The figures show the actual reduction in vibration after implementing corrective maintenance as recommended by the analyst. These are prime examples of adding life and reliability to the machine.

Figure 1 shows an outboard bearing vibration signature as found upon initial inspection. Figure 2 is the same measurement point information after the turbine was balanced. The vibration severity was reduced by nearly 500 percent. The longevity of machine life has been increased substantially. Now, the bearings will be much more reliable and stay in service much longer.

Bearing damage can also be found through vibration analysis. Lack of, or improper lubrication, contamination, mishandling or incorrect installation, incorrect application, or excessive loading causes shortened bearing life. Further, a newly installed bearing should have no indications of degradation in the vibration signature.