Seeking help regarding abnormal turbine operation
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Our company has been operating in an isolated grid since 2002; currently, we have two steam turbine generator sets in operation, both of which were manufactured by Qingdao Turbine Factory. One of the extraction units is of the C6—3.43/0.49 model; it was put into operation in 2001 and operates steadily. The current electrical load is around 2400 KW, with a condensation rate of 4 tons per hour. The extraction pump is of the CB25—8.83/3.82/0.49 model; it has been in operation since 2009. The current electrical load is around 13,000 KW, with an extraction volume of approximately 20 tons per hour. The extracted steam is sent to the medium-pressure steam header for use by the condenser. This back-pumping unit underwent major maintenance in April and was put into operation on May 10th. The following issues have arisen during operation: when the main steam pressure is below 8.2 MPa, the stroke of the high-pressure hydraulic motor fluctuates frequently between 48 and 52. At the same time, both the steam inlet and extraction flow rates experience significant fluctuations, around 6 tons. The electrical load and speed also show some fluctuations, while all other parameters (vibration, axial displacement, expansion difference, oil temperature, oil pressure, etc.) remain normal. Regarding the above issues, I kindly ask all teachers and experts for their assistance. Thank you so much! Tonight, it seems that the speed of the turbine and the electrical load are also experiencing some fluctuations. Tonight, it seems that the speed of the turbine and the electrical load are also experiencing some fluctuations. Tonight, it seems that the speed of the turbine and the electrical load are also experiencing some fluctuations.
This post was last edited by gzlzhx on 2011-5-27 at 17:03. CB25—8.83/3.82/0.49: As stated by the original poster, the load is 13 MW, which corresponds to approximately 55–60% of the maximum load. I’m not sure how many steam inlet valves there are in your system; it’s likely 4–5 pear-shaped valves. The system is currently at either the third or fourth stage of operation, meaning the overlap between the valve opening stages is not optimal. It’s necessary to adjust this overlap according to the design specifications, and it’s advisable to consult an installation company or the manufacturer for help. In small turbines, the control valves are usually of the lift-type, with multiple valves used for control – one valve being of the conical type while the rest are spherical. The stroke and flow rate of each individual valve change linearly, but this linear relationship does not hold during the initial opening stages or when the valves reach their full open position. Therefore, before the first valve reaches its full open position, the second valve has already started to open, and this pattern continues for all the other valves. The overlap between the opening curves of these valves constitutes the degree of overlap. Ultimately, the opening curve of the control valves should be a straight line without any fluctuations, so as to ensure stable operation of the turbine across different load levels. The degree of overlap between control valves means that when the first control valve opens to half its capacity, the second valve should start to open as well; there must be some overlap between them. The overlap of the speed control valves has a significant impact on the unit; a large degree of overlap can lead to substantial fluctuations in the steam inflow rate and load swings, and after load shedding, it can cause the speed to increase. For plate-type control valves with group valves, the degree of overlap can be easily adjusted during maintenance and installation. However, for control valves with cam-driven valve actuation, there is little room for adjustment on-site; the angle between the various cams in the cam-driven mechanism is pre-set by the manufacturer, and it cannot be changed on site, and it is this angle that determines the degree of overlap.