The Horizontal Steam Turbine For Stationary Plants 1920
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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
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