The Horizontal Steam Turbine For Stationary Plants

ø/here insufficient time was allowed for the separation of impurities from the oil. O il Temperatures After a turbine starts running, the tem- perature of the oil gradually increases and finally becomes constant—in a small turbine, after four hours’ continuous running, and in a large turbine after almost a whole day’s continuous running. The shaft (F, Fig. 4) becomes hot because of the high temperature within the steam casing of the turbine. Therefore, the fric- tional heat of the bearings and contact with the heated turbine shaft raise the tempera- ture of the oil. Most of the heat absorbed by the oil is removed by means of an oil cooler. The resultant temperature of the oil depends partly upon the temperature of the cooling water used, but principally upon the capac- ity and size of the coils in the oil cooler. The larger the size and capacity of the cool- ing coils, the lower will be the temperature of the oil. The cooling water should be pumped through the cooler at low pressure and should be as clean as possible. Otherwise, deposits will form on the cooler pipes and the oil will not be cooled sufficiently. In order to control the lubrication of the various bearings thermometers should be fitted in the return oil pipes from each bearing. The temperature of the oil return- ing from the bearings should be not more than 130 degrees F. Occasionally records have shown a temperature as high as 170 degrees F. This indicates insufficient cooling capacity. In sortie types of turbines experience has shown that the normal oil temperatures are very high. This usually results from too small an oil capacity for the work required and may be influenced by the location of the oil tank adjacent to the steam chest through which high temperature steam is supplied to the turbine. Where the main bearings are water cooled, the temperatures are lowered about 10 de- grees F. In rare cases the main bearings are oil cooled, the oil passing through the cavities in the main bearings before entering the bearing surfaces. The oil or bearing temperatures are im- portant factors in judging the efficiency of the lubrication and cooling, and it is an advisable precaution to take temperature records every hour, as foliows: Temperature of each main bearing or of the oil return from each main bearing. Temperature of o il return from the gear case ofa reduction gear ed turbine. If abnormally high temperatures are re- corded, the following additional temperature readings should immediately indicate the source of trouble. Temperature of the oil before entering oil cooler. Temperature of the o il after leaving o il cooler. Temperature of the cooling water entering oil cooler. Temperature of the cooling water leaving o il cooler. Oil Vapor and Foaming On occasion, atomized oil or oil vapor comes from the bearings and oil tanks, not- withstanding the faet that the bearing tem- peratures are quite normal. The cause of the vapor is the heavy charging of the oil with tiny air bubbles, due to the high speed at which the oil is circulated through the bearings and oil pipes. When the air bubbles burst in the bearings or in the oil tanks, the resultant very fine spray of oil produces the vapor. Atomized oil drawn into the electric gen- erator from the bearings may necessitate costly repairs. The .oil will also deposit over the outside of the main bearings and the turbine frame. The oil return pipes from the bearings or gear case must be large enough to carry away the oil, the oil foam and the oil vapor. If the oil return pipes from the bearings are not large enough for this purpose, a positive remedy for the escape of oil vapor from the bearings is secured by the addition of a pipe, venting the oil reservoir of the bearing at a higher level than the original pipe. The additional pipe will return the oil foam and vapor which the first pipes are unable to handle. Where too great a percentage of make-up oil is added to the system, excessive foaming 13