3.2 Phase 2
This phase covers the remaining 500 MW units and all except the most recent 660 MW units. Compared with Phase 1, it is characterised by a radically different design: the axially-tubed side-mounted condenser. The development of the side-mounted condenser coincided with a general move towards the use steel foundations.
In some arrangements, this becomes a 'pannier' design as shown in Fig 4.5 (c), in which condenser and turbine are separated and connected to each other by short ducts (either rigid or with flexible bellows, depending upon the details of the turbine and condenser support arrangements). In other cases the condenser and turbine are combined to form 'integral' condenser design (Fig 4.5 (d)) in which condenser shell encloses both the condenser tubes and the low pressure turbines.
The side-mounted and integral design styles have several advantages. Compared with the equivalent underslung condenser, the steam flow path between the turbine exhaust and the condenser inlet is wider, and the losses smaller. Because of the reduction in exhaust casing length, the overall length of the machine and condenser can be reduced quite significantly (typically the condenser tubes are about 20 m long). The turbine centreline height above basement, and hence the crane height and overall turbine house height, can also be reduced by, typically, 4 m. However, thes advantages are partly offset by other factors. Their relative importance depends upon the detailed layout adopted, but two of these factors are the increased width of the turbine hall, and the question of acces¬sibility to the LP turbine for maintenance.