12.3.2 Cooling system
The cooling air is provided by a system consisting of oil-free compressers or blowers, distribution and exhaust pipework, supports, valves and control gear, and filters or air conditioning plant.
The system shown in Fig 2.96 employs a single multistage compresser. It is normal to install sufficient capacity to meet the cooling requirements of one turbine only, with pipework provided to enable cooling air to be supplied to any of the units in the station.
It is important that the air supply is filtered to ensure the removal of small particles and also that it is free of any corrosive gases, such as sulphur dioxide and chlorides, as emitted from the stack of fossil-fuelled stations. Moisture separators should also be installed, along with suitable pipework drains to ensure that the air supply is dry.
Figure 2.96 also shows locking double-isolating valves and removable flexible connections which are used to ensure that the forced-air cooling system is fully isolated from the turbine when not in use.