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tric, loose fitting, bronze sleeves, designed to permit the rotor to revolve about its true centre of mass instead of its geometric centre. This effectively dampens all vibration which might occur at starting. The cushioning effect is due entirely to capillary oil films between the shells. In larger turbines running at slower speeds, a simple, self-aligning, babbitted bearing is employed, as in standard, low-speed machinery. All Westinghouse turbine bearings are, however, so liberally proportioned that the shaft floats on an oil film with absolutely no mechanical contact, and this without resorting to forced lubrication.
The returns from the bearings are piped to a strainer and cooling coils before being again pumped to the reservoir. This strainer may be by-passed for a short time to permit cleaning while the turbine is in operation, but, as there is little opportunity for dirt and foreign matter to get into the
oiling system, this is an unusual occurrence.
In the oil cooler, Figure 13, the pipe coil is arranged in the form of a nest of twelve or more sections. These are connected in series and can be removed independently in case of a fault in one of the sections. In this cooler, oil circulates through the pipes with the water outside, and sufficient velocity is maintained to prevent the deposit of impurities. Furthermore, the warmest oil comes first in contact with the coldest water, a condition of maximum efficiency in cooling systems.
The bearing and lubrication system of this turbine is the result of an elaborate series of experimental tests on various lubricants and metals conducted for several years on full-sized models suited to a machine of 10,000 kilowatts capacity. The bearing tests were in each case carried out to a point of failure, and the results indicated a large margin of safety in the present bearing proportions.
It is a well-known fact that, even after several years' service, the original tool marks may be found on these bearings, which speaks for itself. It has never been found necessary to fit removable sleeves to the shafts of Westinghouse-Parsons turbines. in order to localize the damage due to bearing failure.
Water Glands. For the maintenance of good vacuum, some form of good shaft packing is absolutely necessary to prevent
air leakage. For this purpose a mechanical packing has proven unsuitable, and in a certain type of packing largely used at present, the air leakage at light loads is so excessive as to vitiate the vacuum one or two inches. Figure 14 illustrates a type of packing gland which absolutely prevents air or steam leakage. Upon the shaft is mounted a gland runner or paddle wheel, which runs in a circular recess shown at the ends of the casing in Figure 5. A small stream of water is admitted to the centre of this propeller, which, when running, forces the water to the outside and maintains a perfect water-seal The corrugations on either side of the propeller are of assistance at the start to confine the gland water until the turbine has been brought up to full speed. In this gland the clearances are radial so as to permit a considerable amount of shaft movement.
Generator Coupling. A small, but important detail is shown in Figure 15, illustrating a standard generator coupling partly dismantled. The actual bearing surfaces through which torque
is transmitted, may be seen at the ends of the outer sleeve. The part at the extreme left, shown disengaged from the coupling sleeve, is forced and keyed on to the turbine shaft; a similar part on the generator shaft. Thus torque is transmitted through eight radial surfaces at each end of the coupling, which provides all the flexibility desired in direct connected machines having more than two bearings. This coupling is divided at the centre, as shown, in order to permit turbine spindle to be removed independently.
Turbo Generators. In the direct connected turbo generator may be found the most important factor limiting the general design of the turbine itself. At standard frequencies, the number of running speeds possible is reduced to comparatively narrow limits, viz., 3,600, 1,800, 1,200 and 900 revolutions per minute for 60-cycle service and 3,000, 1,500, and 750 revolutions per minute for 25-cycle service. Fortunately, the turbo generator design permits of high running speeds without incurring disadvantages in loss and mechanical strength.
Outside of its small dimensions, the turbo generator follows the standard design of alternating current apparatus, so that we need consider but two points. First. The rotating field in the
smaller sizes consists of a solid cylinder of steel with copper strap windings imbedded therein, so that the field presents a smooth cylindrical surface which greatly reduces the loss from air friction. The ends of the field are capped by non-magnetic material into which the end of the field shafts are forced under hydraulic pressure. Second. The ventilation of the generator is mechanically provided for by means of ventilating fans mounted upon the field shaft, as shown in Figures 4 and 16. Here one-half of the air chamber fitted to each end of the generator has been removed to show the fan and winding.
Air ducts beneath the turbine communicate with these fans and it is well to note here that whatever the temperature of the engine room, the generator is always supplied with a positive draft of pure, cold air from the outside. This positive ventilation is, perhaps, the most important feature of the Westinghouse turbo generator and is responsible for the high over-load capacity shown by this machine. For example, during a serious accident occurring last year at the Waterside station of the New York Edison Company, a 7,500 kilowatt Westinghouse-Parsons turbine sustained practically the entire 60-cycle load, of from 13,000 to 14,000 kilowatts for one hour and twenty minutes. This corresponds to an overload of practically 80 per cent., while the machine is usually guaranteed to sustain 50 per cent. overload for one hour.
Turbine Testing. The policy of thoroughly testing out each prime mover before leaving the builders works, has been rigidly adhered to. In the case of large turbines, a boiler plant sufficient to maintain 50 per cent. overload on the 10,000 kilowatt machines would evidently be out of the question. Up to 5,000 or 6,000 horse power capacity, however, every turbine is tested under approximately the same conditions as would obtain in practice. For this purpose, surface condenser equipments are maintained, the condensed steam being measured by actual weight. Independently fired superheaters similarly provide any desired temperature of steam supply. A typical view of a turbine arranged for test is shown in Figure 17. Here power