Regarding Steam Turbine Vacuum

The lowest value of vacuum is the boiling pressure corresponding to the temperature of the applied cooling water. Refer to a set of steam tables for full information.

If the vacuum is somewhat weaker than this figure, then there is a leak of non-condensibles, such as air, into the condenser, steam side of the heat exchange surfaces. Just fix the leak.

There is little <...harmful...> effect on the equipment, however, the effect on the economics of operation can be anything in the range from "annoying", passing through "serious", all the way to "closure-of-business-operation".

What are the UNITS (inHg, inH2O, mmHg, mmH2O) ??? Is the Steam Jet/Hybrid Air Ejector vacuum system working properly to remove the air from the main condenser ?

The very worst condition, aside from the condenser filling up with water and hitting your rotating blades, is excessive moisture in the steam impinging on the rotor and stator vanes and breaking some blades. You will be putting through an excess of steam since you're not withdrawing all the energy at the LP turbine and may not be able to handle the excess condensate.

could you please confirm the exhaust pressure value you have mentioned. Your gauge scale should be reading like this 0 (atmospheric) and reducing in steps of 0.1 towards perfect vacuum and the scale should be reading like this 0, -0.1,-0.2, -0.3.........-1.0 (which is perfect vacuum). -0.61 seems to be a better value if the scale reads the way I have mentioned.

Any way have you verified all the potential leaking (ingress) sources such as your PVRV (Pressure vacuum relief valve) seal water flow, Ingress through valve packings, Ejector and Ejector condensor healthiness, adequate cooling water flow to the surface condensor etc.

Thanks for all ur response, (1) Our Cooling water is of poor quality (Cond : >8000 Microsiemens) and much scale formation in tubes. (2) Confirmed no any air ingress in the system. (3) Vacuum pump is used ,,it expels steam with air...seal water become very hot.(4) Turbine Exhaust Temp : 74 degC and Vacuum = -0.61 KSC. Earlier before the vacuum was -0.90 KSC for full load (33 MW) , Now for partial load itself (20 MW) it is -0.61 KSC.