Turbine Efficiency

If there is cavitation in the condensor, then it may damage the vacuum pumps of condensor. So cavitation limits the condensor vacuum.

Refer to steam tables, as pressure and temperature are intimately related. To obtain more vacuum, lower the temperature at the condenser.

Basically your statement is correct if you refer only to the steam turbine efficiency. Overall efficiency of the system is a bit more complex, because any heat that you remove from the condensate has to be put back in the boiler.

There are practical limits to the vacuum that can be achieved, due to the ingress of incondensables (air) etc. Condensate pumps can survive without cavitating as long as there is some sub-cooling but the penalty is as above.

The other limiting factor could be the turbine design where the load across the last blades caused by the difference in pressure across them could be too great and therefore the turbine manufacturer may specify a limit to the allowed vacuum.

As mentioned temperature and vacuum are the criteria for setting the efficiency of the steam cycle plant. Most turbine manufacturers base their 'plated' efficiency on the condenser water temperature being 60F and the vacuum at 28" Hg. Colder water will usually benefit the process as the vacuum being 'pulled' will increase.

Engineers of steam powered vessels hated the warm waters in the tropics as the vacuum suffered and combined with condenser fouling could actually reduce the service speed of the ship.