Turbine Supervisory Instruments
 

[LEFT][F**T=&quot]Turbine Supervisory Instruments[/F**T]

[B]The following supervisory instruments are furnished with the unit and are to be observed during start-up, operati** and shutdown. We will explain the following instruments in detail as follows.[/B]

[U][F**T=Impact]1- Casing Expansi**[/F**T][/U]
[B]As a unit is taken from its cold c**diti** to its hot and loaded state, the thermal changes in the casings will cause it to expand.[/B]
[B]The Casing expansi** scale measures the movement of the force pedestal relative to a fixed point (the foundati**). It indicates expansi** and c**tracti** of the casings during starting and stopping period, and for changes in load, steam temperatures.[/B]
[B]Should it fail to indicate during these transient c**diti**s, the situati** should be investigated? The relative positi** of the fore pedestal should be essentially the same for similar c**diti**s of load, steam c**diti**s, vacuum, etc.[/B]

[U][F**T=Impact]2- Rotor Positi**[/F**T][/U]
[B]Rotor Positi** instrument measures the relative axial positi** of the turbine rotor thrust collar with respect to the first bearing support. The thrust collar exerts a pressure against the thrust shoes, which are located ** both sides of the thrust collar. Wear ** the thrust shoes results in an axial movement of the rotor and is indicated ** these instruments. [/B]
[B]This instrument is equipped with an alarm relay which activates if the rotor moves bey**d a predetermined distance. C**tinued movement bey**d a sec**d predetermined distance activates rotor positi** trip relay which trip the turbine via the emergency trip system.[/B]

[U][F**T=Impact]3- Differential Expansi**[/F**T][/U]
[B]When steam is admitted to a turbine, both the rotating parts and the casings will expand. Because of its smaller mass, the rotor will heat faster and therefore expand faster than the casings.[/B]
[B]Axial clearances between the rotating and the stati**ary parts are provided to allow for differential expansi** in the turbine, but c**tact between the rotating and stati**ary parts may occur if the allowable differential expansi** limits are exceeded. The purpose of the differential expansi** meter is to chart the relative moti** of the rotating and stati**ary parts. It gives a c**tinuous indicati** of the axial clearance while the turbine is in operati**.[/B]
[B]The instrument is equipped with alarm relay which activates if the value reaches the alarm point. As the rotating and stati**ary parts become equally heated after a transient c**diti**, the deferential expansi** will decrease.[/B]

[U][F**T=Impact]4- Rotor Eccentricity[/F**T][/U]
[B]When a turbine has been shut down, the rotor will tend to bow due to uneven cooling if the upper half of the casing enclosing the rotor is at a higher temperature than the lower half. By rotating the rotor slowly ** turning gear, the rotor will be subjected to **** uniform temperature, thereby minimizing bowing.[/B]
[B]This bowing of the rotor is recorded c**tinuously as eccentricity from turning gear speed to approximately 600 rpm. The eccentricity instrument is equipped with an alarm signal which activates when the eccentricity reaches the alarm point.[/B]


[U][F**T=Impact]5-Vibrati**[/F**T][/U]
[LEFT][B]The vibrati** instrument is used to measure and record vibrati** of a turbine rotor at speeds above 600rpm. Below this speed, the rotor bowing is recorded as eccentricity.[/B][B][F**T=&quot]The vibrati**s are measured ** the rotor near the main bearings. Excessive vibrati**s serve as a warning for abnormal and possible hazardous c**diti**s in the turbine. Each vibrati** instrument is equipped with alarm and trip relays which activates when excessive vibrati**s are measured at any **e of the bearings.[/F**T][/B][/LEFT]
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