« ForrigeFortsett »
tion and principles of operation of the WestinghouseParsons steam-turbine.
Ans.--The Westinghouse-Parsons steam-turbine is fundamentally based upon the invention of Mr. Charles A. Parsons, who, while experimenting with a reaction turbine constructed along the bes of Hero's engine, conceived the idea of combining the two principles, reaction
and impulse, and also of causing the steam to flow in a general direction parallel with the shaft of the turbine. This principle of parallel flow is common to all four types of turbines, but is perhaps more prominent in the Westinghouse-Parsons and less so in the De Laval. The cylinder, or stator, as it is termed, is divided longitudinally into an upper and a lower half flanged and bolted together. There are three sections or drums, gradually increasing
in diameter from the inlet to the third and last group of blades. This arrangement may
be likened in some measure to the triple-compound reciprocating engine.
Ques. 739.-Describe the arrangement of the blades or buckets in the Westinghouse-Parsons steam-turbine.
Ans.-There are two kinds of blades, viz., stationary blades and moving blades, but they are similar in shape, being of the same curvature. These blades are made of hard drawn material, and are set into their places and secured by a caulking process. The stationary blades project from the inside surface of the cylinder, while similar rows of moving blades project from the surface of the rotor, or revolving drum. When the upper half of the cylinder is in position each row of stationary blades fits in between two corresponding rows of moving blades.
Ques. 740.—Are these blades all of the same length?
Ans. They are not. The length varies from 1/2 inch for the shortest to 7 inches for the longest, according to their location. The shortest blades are placed at the steam end of each section and the longest blades are placed at the opposite end.
Ques. 741.- What is the clearance between the blades as they stand in the rows?
Ans. The clearance between the blades as they stand in the rows is in.ch for the smallest size blades and 12 inch for the larger ones, gradually increasing from the inlet to the exhaust. In the 5,000 kilowatt machine the clearance at the exhaust end between the rows of blades is 1 inch.
Ques. 742.—What is the general direction taken by.
the steam in its passage through the Westinghouse-Parsons turbine?
Ans.—The steam entering at the smaller end of the cylinder presses first against the shortest blades and then passes on through in the form of spiral or screw line about the rotor, continually pressing against new and gradually lengthening blades, thus doing work by reason of its velocity.
Fig. 201. SECTIONAL VIEW OF FOUR Rows of BLADES, OF A WESTINGHOUSE
Ques. 743.-As steam presses equally in all directions, is there not a very heavy end-thrust exerted by the rotor?
Ans.-There is not. The pressure in either direction is perfectly balanced by means of balancing pistons placed on the steam end of the rotor. The diameters of these pistons correspond to the diameters of the different drums or sections. *
Ques. 744.-About what is the velocity of the steam in the Parsons turbine?
*The theory and action of these balancing pistons is fully and completely described in Swingle's "Twentieth Century Hand Bock for Engineers and Electricians.”
Ans.—The highest velocity does not exceed 600 feet a second.
Ques. 745.--About what amount of pressure is exerted upon each blade by the steam?
Ans.—The steam-thrust on each blade is said to be equal to about 1 ounce avoirdupois.
Ques. 746.—With such a very light pressure upon
each blade, why is it that this turbine is capable of developing power?
Ans. Because of the large number of blades; as, for instance, taking a 400 kilowatt machine, there are 16,095 moving blades and 14,978 stationary blades, a total of 31,073.
Ques. 747.—How are the clearances preserved?
Ans. A rigid shaft and thrust or adjustment bearing accurately preserves the clearances.
Ques. 748.—Describe the construction and action of the bearings.
Ans.—The bearings are construcied along lines differing from those of the ordinary ciprocating engine. The bearing proper is a gun-metal sleeve that is prevented from turning by a loose-fitting dowell. Outside of this sleeve are three concentric tubes having a small clearance between them. This clearance is kept constantly filled with oil supplied under light pressure, which permits a vibration of the inner shell or sleeve and at the same time tends to restrain or cushion it. This arrangement allows the shaft to revolve about its axis of gravity instead of the geometrical axis, as would be the case if the bearing were of the ordinary construction. The journal is thus to a certain degree a floating journal, free to run slightly eccentric according as the shaft may happen to be out of balance.
Ques. 749.—How is the power of the WestinghouseParsons turbine transmitted to the dynamo, or other machine to be run?
Ans.—A flexible coupling is provided, by means of which the power of the turbine is transmitted to the dynamo or other machine it is intended to run. The oil from all the bearings drains back into a reservoir, and from there it is forced up into a chamber, where is forms a static head, which gives a constant pressure of oil on all the bearings.
Ques. 750.—How is the speed governed?
Ans.-The speed of the Westinghouse-Parsons turbine is regulated by a fly-ball governer constructed in