Turbine Auxilaries Q & A-v

81. Steam blowing from a turbine gland is wasteful. Why else should it be avoided?
Answer: It should be avoided because the steam usually blows into the bearing, destroying the lubrication oil in the main bearing. Steam blowing from a turbine gland also creates condensate, causing undue moisture in plant equipment.
82. Besides lubrication, which are two functions of lubricating oil in some turbines?
Answer: In large units, lube oil cools the bearings by carrying off heat to the oil coolers. Lube oil in some turbines also acts as a hydraulic fluid to operate the governor speed-control system.
83. What is meant by the water rite of a turbine?
Answer:
84. It is the amount of water (steam) used by the turbine in pounds per horsepower per hour or kilowatts per hour.
85. What are five types of condensers?
Answer:
1. Surface (shell-and-tube).
2. Jet condenser.
3. Barometric condenser.
4. Air-cooled condenser.
5. Evaporative condenser.
86. Why is there a relief valve on a turbine casing?
Answer: The turbine casing is fitted with spring-loaded relief valves to prevent damage by excessive steam pressure at the low-pressure end if the exhaust valve is closed accidentally. Some casings on smaller turbines are fitted with a sentinel valve, which serves only to warn the operator of over-pressure of the exhaust end. A spring-loaded relic valve is needed to relieve high pressure.
87. Why must steam turbines be warmed up gradually?
Answer: Although it is probable that a turbine can, if its shaft is straight, be started from a cold condition without warming up, such operation does not contribute to continued successful operation of the unit. The temperature strains set up in the casings and rotors by such rapid heating have a harmful effect. The turbine, in larger units especially should be warmed slowly by recommended warm-up ramp rates because of close clearances.
88. What should you lost vacuum while operating a condensing turbine plant?
Answer: If vacuum is lost shut down immediately. The condenser cannot stand steam pressure, the condenser tubes may leak from excessive temperature. Excessive pressure will also damage the shell, the exhaust and the low-pressure parts of the turbine.
89. What are the main causes of turbine vibration?
Answers:
1. Unbalanced parts.
2. Poor alignment of parts.
3. Loose parts.
4. Rubbing parts.
5. Lubrication troubles.
6. steam troubles.
7. Foundation troubles.
8. Cracked or excessively worn parts.
90. What is the purpose of a turning gear?
Answer: Heat must be prevented from warping the rotors of large turbines or high-temperature turbines of 400°C or more. When the turbine is being shut down, a motor-driven turning gear is engaged to the turbine to rotate the spindle and allow uniform cooling.
91. What does he term "ramp" rate mean?
Answer: Ramp rate is used in bringing a turbine up to operating temperature and is the degrees Celsius rise per hour that metal surfaces are exposed to when bringing a machine to rated conditions. Manufacturers specify ramp rates or their machines in order to avoid thermal stresses. Thermocouples are used in measuring metal temperatures.
92. What is the difference between partial and full arc admission?
Answer: In multi-valve turbine inlets, partial arc ad mission allows the steam to enter per valve opening in a sequential manner, so as load is increased, more valves open to admit steam. This can cause uneven heating on the high-pressure annulus as the valves are individually opened with load increase. In full-arc admission, all regulating valves open but only at a percentage of their full opening. With load increase, they all open more fully. This provides more uniform heating around the high-pressure part of the turbine. Most modern controls start with full-arc and switch to partial arc to reduce throttling losses through the valves.
93. What are some common troubles in surface-condenser operation?
Answer: The greatest headache to the operator is loss of vacuum caused by air leaking into the surface condenser through the joints or packing glands. Another trouble spot is cooling water leaking into the steam space through the ends of the tubes or through tiny holes in the tubes. The tubes may also become plugged with mud, shells, debris, slime or algae, thus cutting down on the cooling water supply. Corrosion may be uniform, or it may occur in small holes or pits.
94. Where would you look for a fault if the air ejector didn't raise enough vacuum?
Answers:
1. In this case, the trouble is usually in the nozzle. You will probably find that the nozzle is eroded.
2. The strainer protecting the nozzle is clogged.
3. The steam pressure to the nozzle is too low.
95. How would you stop air from leaking into a condenser?
Answer: First find the leak by passing a flame over the suspected part while the condenser is under vacuum. Leaks in the flange joints or porous castings can be stopped with asphalt paint or shellac.
96. Do you stop cooling water flow through a steam condenser as soon as the turbine is stopped?
Answer: You should keep the cooling water circulating for about 15 minutes (also see the manufacturer’s recommendation) or more so that the condenser has a chance to cool down gradually and evenly. Be sure to have cooling water flowing through the condenser before starting up in order to prevent steam from entering the condenser unless it is cooled. Overheating cause severe leaks and other headaches.
97. How would you stop a leaky tube in a condenser that was contaminating the feed water?
Answer: To stop leaky tube from contaminating the feedwater, shut down, remove the water-box covers, and fill the steam space with water. By observing tube ends, you can find the leaky tube. An alternate method is to pressurize (30 kPa) the steam space with air. Then flood the water boxes to the top inspection plate and observe any air bubbles. Once you have found the leaky tube or tubes, drive a tape bronze plug (well-coated with white lead) into each end of the tube to cut it out service. This allows you to use the condenser since the tubes need not be renewed until about 10 percent of the tubes are plugged.
98. Why must condensate be subjected to salinity tests where brackish cooling water used?

Answer:
Condensate may leak from the cooling-water side to the steam side of condenser and contaminate the feedwater, thus causing scale to form in the boilers, brackish cooling water may leak into the steam space from cracked or porous tubes or ruin around the joints at the end of the tube ends, etc. By taking salinity readings of the condensate, leaks may be found before they can do any harm.