Electric Propelling Machinery for U. S. S. Tennessee BY WILFRED SYKES

General Engineer, West inghouse Electric & M f g . Co.

THE U. S. S. Tennessee, which is now rapidly approaching completion, will be the second battleship to be equipped with electric propulsive

machinery. The New Mexico, which was placed in operation about a year ago, has demonstrated the suc-cess of this system of propulsion. The U. S. S. Ten-nessee differs in a number of respects from the U. S. S. New Mexico, mainly in connection with the layout of the machinery and the details of the electrical appara-tus installed. The New Mexico was originally designed for direct-connected turbines and was adapted to electric drive with minor structural changes. Full advantage was not taken, therefore, of the characteris-tics of electrical drive which allow of the apparatus to be disposed in the most suitable manner. In the case of the U. S. S. Tennessee full advantage has been taken of the flexibility in the arrangement of the electrical machinery, and therefore this ship will be the first which will illustrate completely what can be done with electric drive.

Various claims have been made for electric drive, basing its superiority upon questions of economy, maneuvering capacity and such characteristics. It is believed, however, that the greatest advantage of electric drive for battleships is the ease with which it can be arranged to give the greatest protection to the machinery and the best construction of ship. It can be stated without exaggeration that the use of electric drive would be justified from this standpoint if in other respects it did not compare with what had been pre-viously used, as it is of fundamental importance that the machinery shall be reliable and protected in such a manner as to be as free as possible from injury when in action. The protection given the machinery in the case of the U. S. S. Tennessee by means of numerous bulk heads, is very much superior to anything done before in ships of this class, so that it is practically impossible to put the machinery out of operation either by gunfire or by torpedo attack.

The propelling machinery for the U. S. S. Tennessee consists of two turbo generators and four propelling motors. The switching apparatus is so arranged that either generator can drive all four motors, or that the two generators in operation each will drive two motors. The motors are grouped in pairs on either side of the ship so as to facilitate maneuvering. The turbo generators have a combined capacity of about 26,500 kw., which will be required to drive the motors when operating under the maximum conditions, each motor then delivering 8375 h.p. The speed of the motors is varied by varying the revplutions of the turbine within certain limits, and the motors also have two sets of poles, so that with the turbine running at full speed there is a speed reduction of about 12 to 1

and 18 to 1 to the propellers. With the motors run-ning at the lower speed only one generator is used, and a speed up to 15 knots is obtained under this condition. As ships of this type operate mainly at speeds of 15 knots or less, the average operating economy is very greatly improved by the possibility of so dividing the power equipment that the best efficiency can be obtained at full speed or about % speed.

M A I N PROPELLING M O T O R WITH B L O W E R S ASSEMBLED IN F A C -

TORY

The turbines are designed to operate with a steam pressure of 250 lb. per sq. in., 50 deg. superheat and with a vacuum of about 28 Yi in. They are of the semi-double-flow type, steam being first expanded in suitable nozzles and flowing through an impulse wheel with two rows of blades. It then expands further through a set of reaction blading until the volume of steam is such as to render it inconvenient to handle, when it is divided and flows through two sets of reac-tion blading at either end of the turbine. The turbine speed under normal operating conditions is about 2130 rev. per min. maximum, and on test the machine has been run to 2480 rev. per min. The speed of the turbine is varied by means of a specially designed

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January 1920 S Y K E S : E L E C T R I C P R O P E L L I N G M A C H I N E R Y 5*

M A I N T U R B I N E ON T E S T FLOOR COUPLED TO W A T E R B R A K E

governor which, instead of being loaded by a spring as is usual, is arranged so that the centrifugal weights act against an oil pressure on one side of a piston. With such an arrangement the speed at which the governor will affect the steam supply will vary with the oil pressure, and by varying this pressure, the turbine can

be set to run at any speed desired. A specially designed variable pressure valve is provided in the control room, for the purpose of operating the governors, and the only connection between the control room where the speed is varied and the turbine room is an oil pipe connecting to the governor piston.

CONTROL EQUIPMENT ASSEMBLED IN FACTORY

5 4 S Y K E S : E L E C T R I C PROPELLING M A C H I N E R Y Journal Α. I. Ε. Ε.

The generator is a three-phase machine wound for 3400 volts and operates at about 35 cycles at full speed. It is of the usual construction for machines of this size, except that special provisions have been made to avoid salt deposits in the windings. This is a trouble which is likely to occur where machines are operated in salt laden air.

The motors are designed with two sets of poles, being connected for 24 poles for full speed and for 36 poles for cruising. The stator has two separate windings and the rotor has a single winding which is so arranged that it is a polar winding for 24 poles and a short circuit winding for 36 poles. The winding has cross connec-tions arranged in such a manner that they act as equalizer connections for 24-pole connection of the stator, and as short circuiting connections for the 36-pole connection. The motor is started as a wound-rotor machine by means of a liquid rheostat, and in case it is desired to run on 36-pole connection the machine is switched over to this pole connection.

The operation of the ship is controlled by the switching regulating apparatus in the control room. Cables from the generators are brought into this room, passing through the necessary switches to the motors. The secondary leads from the motors are also brought through liquid rheostats which are located in the con-trol room. All necessary instruments for the operation of the equipment and the measurement of the power are located in this room, and the necessary telegraphs and other communicating devices are suitably located so as to facilitate communication with the navigating officers. All switching is done by means of oil immersed switches, and while normally circuits will be broken with the field of the generator disconnected, the switches are of such construction that they can be operated under full power. The variable pressure valves for operating the turbine governors are located in this room, as well as the rheostats for varying the field of generators.

The field of generators is controlled through a machine which is arranged to buck or boost the 240-volt direct-current power circuit of the ship. This booster is motor driven and the exciting voltage is varied through the booster field which is reversible.

The guarantees for this ship based on 250 lb. steam pressure, 60 deg. circulating water with no superheat are as follows:

21 knots 11.9 lb. 19 " 11.65 " 15 " 12.1 " 10 " 15.45 "

These figures include all the power required for driv-ing the circulating pumps, condensate pumps, ventila-ting blowers for machines and excitation.

PRODUCE AND SAVE

IT is coming to be more and more widely recognized that the only effective remedy for the abnormal economic conditions which have resulted in succes-

sively higher prices and higher wages lies in increasing production and increasing savings. Produce all you can and save all you can is the solution of the present economic difficulties, and this thought is admirably expressed in the following paragraphs by Albert W. Atwood in the Saturday Evening Post:

"The only way to break the vicious circle is by the slow, painful process of work and save throughout the world. In time, Europe will be able to supply her own needs. In time, the supply of goods will catch up with demand, and then we shall have gradual deflation in place of inflation, because it will be possible slowly to pay off the world's debts and the bank credits based upon them.

"Patent nostrums, whether they apply to business men on the one hand or to the wage earner on the other, will only lead up blind alleys. Improved machinery, more scientific devices, better organization of industry, more economic distribution of its products, better train-ing of the worker, more democracy in industry and more good will between capital and labor—all these will help. But they take years, generations perhaps, to bring about, and patent schemes to rush them into being are pitifully futile.

"And as for working and saving, the bitter truth is that this doctrine will prove our salvation only if people learn that it applies to themselves as well as to the other fellow."

PLANS FOR DISABLED SOLDIERS

It is announced that the War Department, Federal Board for Vocational Education, and Civil Service Commission will within a few weeks have completed a plan they have had under consideration for some time, one of cooperation whereby the employment under the War Department of partially disabled sol-diers, including those who ordinarily would be barred from civil positions because of their physical condition, will be facilitated in every way possible, and which will permit the employment of partially disabled men on same basis as those who have not sustained physical injury. War Department has considerably more than 100,000 civilian employees in its various establishments, and it is believed by Government officials that this large force can absorb several thousand partially dis-abled men without serious detriment to the service.