Page 370 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Steam Turbines and Turboexpanders 349

7. As soon as the rotor is in motion, turn on the water to gland con-
denser and steam to the ejector. Close all atmospheric casing
drains to prevent drawing air through the drains when partial vac-
uum is established.
8. Start the second stage air ejector or the priming ejector if one is
used.
9. Keep the turbine rolling at low speed-approximately 200 to 400
rpm-to allow the parts to become partly heated. Maintain this
slow rolling about 20 minutes. The duration of the rolling period
depends on the straightness of the rotor which, in turn, depends
somewhat on the length of the previous shutdown. If the machine
has been shut down long enough to become thoroughly cooled, the
rotor should be straight. However, after shorter shutdowns-such
as 4 to 8 hours-the machine is only partly cooled and the rotor
may be distorted. In such cases, continued rolling at low speed
will heat the rotor uniformly and straighten it.
10. At the end of the rolling period, bring the unit up to speed slowly,
taking 10 to 15 minutes to reach full speed.
After the unit comes up to speed, reduce the speed again and
slow roll the turbine for a somewhat longer period of time.
11. Shut off the priming ejector, if one is used. When the maximum
vacuum is obtained with the second stage ejector, start the first
stage ejector.
12. Make sure that the governor properly controls the speed of the tur-
bine with full steam pressure and vacuum.
13. Close the drains from pressure zones when it is assured that all
water has been removed and condensation stopped.
14. Make certain that the temperature of the oil supply to the turbine is
maintained between 110 and 120°F. The temperature of the oil
leaving the bearings should not exceed 160°F.
15. Open throttle valve fully.
16. Make sure that the governor properly controls the speed of the tur-
bine with full steam pressure.

Test of Overspeed Ttlp. When the turbine is first started after installation,
it is very important to test the overspeed trip by actually overspeediig the
machine. This may be done by use of the overspeed test device on the top
of the governor. See the governor instructions for +ration.
The overspeed trip should operate at approximately 10 percent above
normal full speed. Where a speed changer is provided, the trip should
operate at 10 percent above the upper limit of the speed changer. The
proper tripping speed for each specific application will be found in the
“special information” section of the instruction book and also stamped