MIL-HDBK-1003/7
Automatic Extraction Type. Automatic extraction turbines usually operate with
5.3.1.3
high pressure, high temperature throttle steam supply to a high pressure turbine
section. The exhaust pressure of the high pressure turbine is held constant by means of
automatic extraction gear (valve) that regulates the amount of steam passing to the low
pressure turbine. Single automatic extraction turbines provide steam at a constant
pressure from the automatic extraction opening, usually in the range of 50 to 150 psig
(345 to 1034 kPa gage). Double automatic extraction turbines consist of a high,
intermediate, and low pressure turbine section and provide steam in the range of 50 to
150 psig (345 to 1034 kPa gage) at one automatic extraction opening and 10 to 15 psig
(69 to 103 kPa gage) at the other automatic extraction opening. Automatic extraction
turbine generators operating automatically meet both automatic extraction steam and
electrical demands by adjusting the flow of steam through the low pressure turbine. A
typical automatic extraction cycle is shown in Figure 19.
Automatic extraction turbines may be either condensing (condenser pressure
1.0 to 4.0 inches of Hg Abs.) or noncondensing (usually 5 to 15 psig (34 to 103 kPa
gage) back pressure).
Mixed Pressure or Induction Type. The mixed pressure or induction type
5.3.1.4
turbine is supplied with steam to the throttle and also to other stages or sections at a
pressure lower than throttle pressure. This type of machine is also called an admission
type. The steam admitted into the lower pressure openings may come from old low
pressure boilers, or it may be the excess from auxiliary equipment or processes. The
mixed pressure turbine is the same as an automatic extraction turbine described in
5.3.1.3 above, except steam is admitted instead of extracted at the automatic controlled
opening.
Low Pressure Type. Low pressure turbines are those with throttle pressures
5.3.1.5
generally below 400 psig (2758 kPa gage). However, the pressure dividing point varies,
depending on the manufacturer and type of turbine (industrial, mechanical drive, etc.)
The variations as described in 5.3.1.1, 5.3.1.2, and 5.3.1.3 above are also applicable
to low pressure turbines.
5.3.2
Noncondensing Types
5.3.2.1
Superposed or Topping Type. Refer to para 5.1.3.3, and Figure 14 in this
handbook for a description of topping turbine and cycle.
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