2. .egative sequence
3. .everse power
4. .ockout relays
5. Generator ground relay
6. .oltage-controlled overcurrent relay
Condition .onitoringSystems
Predictive performance-based condition monitoring isemerging， as amajor maintenance technique， with large reduction in maintenance costs as shown in Figure 19-7. The histogram shows that although an approximate one-third reduction in operating and maintenance (..M) costs was achievedby moving from a ..corrective，.. more realistically termed a ..breakdown..
1.00
0.75
0.50
0.25
Figure 19-.. Comparison between .arious maintenance tec.ni.ues.
Corrective Preventive Predictive
or ..fix as fail.. repairstrategy， to a ..preventive..regime， this yielded only approximately half of the maximum cost savings. Although more difficult to introduce than the simple scheduling of traditional maintenance activitiesrequired for preventiveaction， the Electric Power .esearch Institute (EP.I) research showed that the introduction of ..predictive.. maintenance strategies could yield a further one-third reduction in ..M costs.
The introduction of the total maintenance condition monitoring systemmeans the use of composite condition monitoring systems， which combine mechanical and performance-based analysis with corrosion monitoring. These three components are the primary building blocks that enable the introduction of a comprehensive plant-wide condition management strategy.
.umerous case studies have shown that many turbomachinery operational problems can only be diagnosed and resolved by correlating the represent-ative performance parameters with mechanical parameters.
In plant healthterms， monitoring and measurement both cost moneyand are only half way to the realobjective， which is the avoidance of cost and plant damage. Condition management makes proper use of both activities and exploits information derived from them to generate money for the plant operator. Good plant conditionmanagement，therefore， should be the objective of materials and machine health specialists.
The change has further implications: in thepast， corrosion and conditionmonitoring were considered to be service activities， providing only a reacti.e strategy. Condition management embodies a pro-acti.e stance on plant health. This fundamental understanding should not go unrecognized by the materials and condition monitoring specialists. Condition management is a huge opportunity for technical specialists to provide the best possibleservice toclients， whether internal or external. The same specialists also will be able to derive the maximum direct benefit from their expertise.
Conventional alloy selection， coating specification and failure investiga-tion skills will always be required， as will inspection services to confirm thecondition of the plant. However， the phenomenon labeled corrosion should no longer be regarded as a necessary evil as it is only a problem when out of control. The electrochemical behavior characterizing corrosion is also the means by which on-line plant health management can be achieved.
Major power plant complexes contain various types of large machinery.Examples include many types of machinery， in particular gas and steamturbines， pumps and compressors， and their effect on the Heat .ecoverySteam Generators (H.SG)， condensers， cooling towers， and other majorplant equipment. Thus， the logical trend in condition monitoring is to multi-machine train monitoring. To accomplish thisgoal， an extensive database， which contains data from all machine trains along with many composite multi-machine analysis algorithms are implemented in a systematic and modular form in a central system.
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