Steam Turbine Construction

In this program on steam power we  have examined steam production and the  different types of boilers and fossil  fuels which are used for this purpose we  are now going to shift the focus on to  steam utilization by taking a detailed  look of the steam turbine which drives  the electrical generator we already  studied the various turbine cycles and  factors affecting efficiency at the beginning of this program.

In this module  we'll look at the main features of  turbine construction including the  various components and support systems  such as gland steam lube and hydraulic  oil and the condenser the subject of  turbine operation control and protection  will be dealt with in the next module  the steam turbine is certainly one of  the most popular prime movers especially  for driving large power generators the  size of steam turbines built and  installed runs all the way from about  megawatts up to  megawatts or more, so what is it that makes the steam  turbine the preferred prime mover in  comparison with say the diesel engine  well.

There are quite a number of  advantages the main factor being that of  physical size for example of   megawatts steam turbine is probably  smaller than a  megawatt diesel another  advantage is that the steam turbine is  far less complicated and contains very  few moving parts the moving parts are  the rotor which drives the generator and  the steam control valves and control  gear the amount of vibration produced by  a steam turbine generator and trans  the surrounding area is relatively low  provided of course that the machine is  in good condition and is correctly  installed and aligned this makes for a  quieter operating plant particularly  when compared with the diesel engine or  even the gas turbine the steam turbine  runs at high speed usually  rpm in  North America or  rpm in Europe and  can therefore be coupled directly to a  two pole generator remembering that the  diesel engine operates at around  rpm.

We can see one of the reasons why the  specific output of the steam turbine is  much greater  one other advantageous factor is the  relative ease of controlling the output  of the steam turbine  this is achieved simply by adjusting the  amount of steam admitted to and flowing  through the turbine as we'll see later  Admission valves also known as control  valves are installed for this purpose  the turbine stop valve or valves is  located upstream of the control valves  in case of an emergency the stop valve  closes automatically cutting off all  steam supply to the turbine and bringing  the machine to a halt this sketch shows  us the major components of a   megawatt reheat turbine we see here the  rotor and the inner and outer casing or  shell this casing surrounds the rotor  leaving very fine clearances between the  stationary and moving parts the  objective of the inner casing is to  direct the steam through the turbine.

The inner casing is fitted into the upper  and lower half of the outer shell which  in turn is supported on a heavy  reinforced concrete base the base must  be firm enough to ensure rigidity that  is it must permit no movement in the  vertical plane which could upset the  alignment of the machine the support  bearings are allowed restricted movement  in the axial plane to cope with  expansion  the turbine as we shall see later other  components noticeable here are the  governor pedestal which supports the  front end bearing and the governor  system in this particular machine steam  from the stop valve is fed into steam  chests located on either....