Steam Turbine Questions

Sounds like homework!!!!

you have Hit it on the nail

Dear Mr.subranshshekar,

1.Your Question No.1 "How the condenser vacuum can be maintained by controlling cooling water temperature &velocity of flow of cooling water in the condenser"

ANS: The HEAT TRANSFER from the steam entering in to the condenser to the Water is the DECIDING CRITERION. The Temp. Rise in the Cooling Water should be maintained as per the Manufacturer's Recommendations.

2. Your Question No.2 "what is hunting & how it occurs"

ANS: Hunting is VARIATION IN TURBINE SPEED in a constant manner or intermittently with considerable low and higher speeds than the rated speed. REASONS: 1. THE Turbine Governor is TOO SENSITIVE, to control this problem, the Governor to be adjusted to be a little SLUGGISH. 2. VARIATION in LOADING PATTERN itself,will lead to Hunting. 3. High Fluctuation in the Steam Parameters, entering the Turbine.

3. Your Question No.3 "what is differential expansion"

Ans: This is a wide subject in different context. However, as I understand from your posting, for this particular ISSUE, the Turbine before starting is to be WARMED-UP, in a CAREFUL and CONTROLLED MANNER, as the Turbine Rotor, Casing etc. expands, uniformly. If the warming-up is not uniform and speeded up, the Thermal Expansion will show different expansion values at different portion of the Turbine, which will lead to problem. The Turbine Water Rating is the index for proper warm up.

4. Your 4th Question "if the exhaust pressure is maintained below the atmospheric pressure in back pressure turbine what will be the effect"

ANS: Very correctly speaking, the Exhaust Pressure of the Turbine is TO BE STRICTLY MAINTAINED AS PER THE DESIGN VALUE. If exhaust pressure goes down below, the Sp. vol of the Steam WILL INCREASE and HENCE THE VELOCITY OF THE STEAM will INCREASE, which MAY LEAD TO DAMAGE THE BLADES, INCREASE VIBRATION LEVEL etc. The Output of the Turbine will INCREASE,since THE HEAT DROP WILL BE MORE. In this case, the DISADVANTAGES are MORE than the ADVANTAGE of ADDITIONAL POWER OUT PUT.

DHAYANANDHAN.S