Question Set 47
Question No. 1
How can problems of "excessive vibration or noise" due to piping strain be avoided on steam turbines?
Answer:
1. The inlet as well as exhaust steam lines should be firmly supported to avoid strains from being imposed on the turbine.
2. Adequate allowance should be made for expansion of steam pipes due to heat.
Question No. 2
How can the detection of deposits in a turbine be made during operation?
Answer:
1. Pressure monitoring.
2. Internal efficiency monitoring.
3. Monitoring exhaust steam temperature.
1. Monitoring specific steam consumption.
Question No. 3
How can the disadvantages of the impulse turbine be overcome?
Answer:
1. By Velocity compounding
2. By Pressure compounding
3. By Pressure-Velocity compounding.
Question No. 4
How can the misalignment be rectified?
Answer:
The bolts holding the flanges together are to be tightened. The coupling is to be checked for square between the bore and the face. At the same time axial clearance is to be checked. Using gauge block and feeler gauges, the gap between coupling faces 1800 apart is to be measured. After rotating the coupling-half 1800, the gap at the same points is to be measured. After this, the other coupling is to be rotated 1800 and the gap at the same points is to be re-measured. These measures should come within a few thousands of an inch. Dividing the coupling faces into four intervals, the distance between the coupling faces at this intervals is to be measured with the aid of a gauge block and feeler gauges. These gaps measurements should come within 0.005 inch for proper angular shaft alignment. After proper alignment at room temperature, the two halves of the coupling are to be connected.
Question No. 5
How can the speed variation be reduced by making a governor droop adjustment?
Answer:
If the internal droop setting is increased, the speed variation will reduce.
Question No. 6
How does improper governor lubrication affect? What is the remedy to it?
Answer:
In the event of low governor oil level or if the oil is dirty or foamy, it will cause improper governor lubrication.
The remedy is:
1. The dirty or foamy lube oil should be drained off; governor should be flushed and refilled with a fresh charge of proper oil.
2. In the event of low level, the level should be built up by make- up lube oil.
Question No. 7
How does solid-particle erosion occur?
Answer:
Solid-particle erosion, i.e. SPE occurs in the high-pressure blades. And it takes place when hard particles of iron exfoliated by steam from superheater tubes, reheater tubes, steam headers and steam leads strike on the surface of turbine blades.
Question No. 8
How does the foreign-particle damage of turbine blades arise?
Answer:
It occurs due to impact on blades by foreign particles (debris) left in the system following outages and become steam-borne later.
Question No. 9
How does this modification reduce the vibration fatigue damage?
Answer:
1. Joining the blade segments together at the shroud band increases the length of the arc-to a maximum of 360° that alters the natural frequency of the blade grouping from the operating vibration mode.
2. This design has gained considerable success in commercial service.
Question No. 10
How is a fly-ball governor used with a hydraulic control?
Answer:
As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits and releases oil on either side of a piston or on one side of a spring-loaded piston. The movement of the piston controls the steam valves.