24765-01-01  Case Expansion Transducer Systems

An important position measurement in Turbine Supervisoryinstrumentation(TSl)is case expansion. Case expansion(sometimes referred to as shell expansion) is the thermagrowth of the machine case as it expands during machinestartup and on-line operations. The case expansiontransducer system is typically mounted on the foundation atthe opposite end from where the turbine casing is attachedto the foundation and provides information about the growthof the machine case relative to the foundation.
Case expansion is a parameter that you should use a dualtransducer arrangement to measure. This arrangementprovides information about the position of the sliding feet onthe machine case. A condition that obstructs or jams onefoot could distort the case and damage the machine. Thedual case expansion transducer configuration in conjunctionwith the 3300 or 3500 monitors provides an alarm for thiscondition. The high temperature dual case expansiontransducer configuration is compatible only with the 3500/45Position Monitor.
Case expansion measurements also enable you todetermine whether machine conditions are exceedingexpected temperature growth differentials. This is primarily astartup parameter that determines whether the machinecasing and rotor grow thermally at nearly the same rate.Different rates of thermal growth can cause the rotating andstationary parts of the machine to rub.
The case expansion transducer assembly consists of a linearvariable differential transformer (LvDT), which is housed in aweatherproof, protective enclosure.

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