The Horizontal Steam Turbine For Stationary Plants

Mixed Pressure Turbines Mixed pressure turbines are designed to operate with two sources of steam supply, a low pressure source and a high pressure source. They may be low pressure turbines with additional blacling to utilize high pres- sure steam in case the supply of exhaust steam is not sufficient for the load required; or they may be high pressure turbines Fig. i. The Principle of the Impulse Type Turbine. specially designed to make additional use of a supply of low pressure steam. TYPES Horizontal type turbines are of the im- pulse type, the reaction type, or combine the features of both. The Impulse Type Turbine All expansion of steam takes place in stationary nozzles or steam delivery pipes and the velocity energy thus produced acts directly on the blades of the revolving disk. The principle of the impulse type turbine is illustrated in Fig. i. The high velocity steam from the nozzle (H) impinges on the buckets (F7) of the wheel (F6) revolving it at high, speed. Steam economy is secured with high velocity of the turbine wheel. The capacity of this type of turbine is in- creased either by repassing the steam through another and larger set of buckets arranged in a circular section inside the row of buckets on the edge of the turbine wheel, or by the addi- tion of one or more bucket wheels, which utilize the steam flow after it has passed through the set of buckets fixed in the rim of the first wheel. Single-stage impulse type turbines are built in sizes below 600 hp. Multi-stage impulse type turbines are built in sizes from 500 hp. to 6,000 hp. The Reaction Type Turbine The steam acts both on the moving and the stationary buckets or blades. As it passes through the turbine the steam im- parts a small part of velocity energy by im- pulse at entrance and the greater part by the reactive thrust of expansion, on the blades fixed in the periphery of the revolving rotor. The pressure of steam expansion is more effective than the velocity flow at which it impinges on the blades. The larger size turbines are of the re- action type and operate at speeds as high as 3,600 revolutions per minute. The De Laval, Kerr, Terry, Moore, Par- sons, Curtis, Zoelly, Riedler-Stumpf, Brown, Bovery, A.E.G.,M.A.N., Allis-Chalmers- Rateau, etc.? are adaptations or combina- tions of the impulse or reaction types. Curtis turbines are both vertical and hori- zontal . The differences in design of all horizontal turbines affect only the arrangement of the revolving and stationary disks, the blacling and the steam distribution to the disks; they do not influence the construction of the main bearings nor the methods of lubrication. CONSTRUCTION The Impulse Type of Turbine The impulse type of turbine consists of a wheel case of iron. (A, Fig. 3), cast in two parts, and a rotor (Fig. 2). The Rotor The turbine spindle or shaft is short and of relatively small diameter, but stiff enough 6