The turbine is held on two end journals which are relatively smaller in diameter. The center protion is very heavy (where blading is done). When Turbine is kept idle, there is all likely hood of a sag on the center. This will be especially predominant if the rotor is additionally hot (and hence the YP is lower) which will be the case when the turbine is stopped after running.
This sag will obviously create an unbalance in the rotor which is not advisable.
To avoid this the rotor is slowwly rotated by using of turning gear (also called barring gear) during the shut down period - either continuously (especially during cooling down) or at fixed intervals (during cold shut down periods).
This practice is followed for several similar equipments with similar weight distribution features (thin journals and heavy centers)
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turbine
Re: turbine
