we have a 700 mw steam turbine machine. My question is regarding the exhaust hood temperature trip.

what is the function of turbine exhaust hood at last stage of turbine and what happens if its temperature raises up?

Is it necessary to give trip on high exhaust hood temperature.

 

The function of high exhaust hood temperature trip is prevent damage/failure of the latter stages of the LP turbine.

Increasing temperature would be the result of either:

inadequate flow for the expansion of steam to the exit. this steam will become heated as the latter stages force it towards the condenser.

OR

higher condenser back pressure effecting the pressure drop across the latter stage also resulting in heating due to the extra forces.

the increase heat will weaken the strength of the rotating buckets. the thermal expansion can damage assembly fits and thermal distortion can cause contact between stationary and rotating components plus change bearing support alignment.

in the event of high temperature caused by poor vacuum, the additional force of the steam loading will be applied to heat weaken buckets.

thus high exhaust hood temperature trip should be a critical protection and compromising its function could result in high maintenance repairs.