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50 Technical Questions and Answers for All-round Attendant of Thermal Power Plant (Electric Thermal Control of Boilers) 1. Boiler Major (15 questions) 1. The main purpose of boiler steam-water circulation - to heat water into qualified steam to satisfy the work of the steam turbine. - Take away the heat from the heating surface to prevent over-temperature damage. - Maintain stable drum water level to ensure safe operation. 2. A common phenomenon of unstable boiler combustion - large fluctuations in furnace negative pressure. - Steam temperature and steam pressure change drastically. - The flame dims, flickers, or even goes out. - The chimney emits black/yellow smoke and the burner is coked. 3. What do the three impulses of drum water level refer to - drum water level, steam flow, and feed water flow, which are used to automatically adjust the water level. 4. What does the "four tubes" of a boiler refer to - water wall, superheater, reheater, and economizer. Preventing leakage and tube bursting is the key. 5. The main factors affecting the drum water level - load changes, combustion conditions, feed water pressure, steam pressure, blowdown/water discharge. 6. Why is the temperature difference between the boiler supply water temperature and the drum wall temperature required to be ≤50°C - to prevent excessive thermal stress in the drum from causing cracks or deformation. 7. Where does the heating steam source at the bottom of the boiler come from - usually from the auxiliary steam header or adjacent furnace steam, which is used to start the heater in a cold state. 8. Why should the flame center be adjusted during operation - to control steam temperature, prevent local over-temperature, reduce slagging, and improve combustion efficiency. 9. The hazards of air leakage in rotary air preheaters - increased exhaust heat loss, increased fan power consumption, furnace negative pressure fluctuations, affecting combustion stability. 10. Precautions for soot blowing in the furnace - Confirm that the parameters are stable before soot blowing and increase the negative pressure appropriately. - It is forbidden to stay near the slag scooping machine to prevent the slag from splashing out and injuring people. - After soot blowing, check whether the soot blower is stuck or leaking. 11. Boiler MFT action conditions (core) - Drum water level high III value/low III value, furnace pressure high/low III value, all fuel interruption, induction/supply fan total stop, fire detection total loss, manual MFT. 12. Ways to improve boiler thermal efficiency - reduce exhaust heat loss (control air leakage, clean ash), reduce mechanical incomplete combustion loss (optimize air distribution), and reduce heat dissipation loss. 13. Causes of boiler slagging - low melting point of coal ash, deflection of flame center, insufficient air volume, and excessive local heat load. 14. Reasons why the oil pressure drops when the oil gun is put in - atomization of the oil gun, pipeline resistance, insufficient output of the oil pump. Check the status of the filter and oil pump. 15. The function and principle of fine powder separator-separate pulverized coal and exhaust gas, and increase the concentration of pulverized coal ； Use centrifugal force to separate coarse and fine powders. 2. Steam Turbine Major (15 questions) 16. The hazards of large vibration after turbine rotation - bearing wear, shaft seal friction, blade damage, and in severe cases, rotor bending and equipment damage. 17. Reasons for large turbine vibration - unbalanced rotor, friction of steam seal, unstable oil film, abnormal steam parameters, and coupling center deviation. 18. The harm of excessive turbine expansion difference - the dynamic and static clearance disappears, friction occurs, resulting in damage to the shaft seal and tripping of the unit. 19. Causes of turbine vacuum drop - abnormal circulating water flow/temperature, vacuum pump failure, vacuum system leakage, insufficient shaft seal pressure. 20. Reasons for high turbine exhaust temperature - low load blast, low vacuum, small steam flow, and high exhaust ventilation valve not open. 21. What is "oil film oscillation" of steam turbine - self-excited vibration caused by instability of bearing oil film, which mostly occurs under high speed and light load conditions. It is necessary to increase the oil temperature or adjust the bearing clearance. 22. Steam turbine TSI monitoring content - vibration, axial displacement, rotation speed, differential expansion and eccentricity to ensure the safety of the rotor. 23. Purpose of cold start warm-up of steam turbine - to reduce the temperature difference between cylinder and rotor, reduce thermal stress, control expansion difference, and avoid critical speed. 24. Reasons for large axial displacement of steam turbine - thrust shoe wear, sudden changes in steam parameters, sudden load changes, blade fouling, and abnormal vacuum. 25. Turbine lubricating oil temperature and oil pressure control range - oil temperature: 38–45℃ ； Oil pressure: 0.08–0.12MPa (bearing oil supply) to prevent oil film damage. 26. Steam turbine overspeed protection (OPC/ETS) - OPC: 103% rated speed, close the adjustment door ； ETS: 110% rated speed, tripping and shutdown. 27. The phenomenon and treatment of turbine water impact - Phenomenon: Sudden drop in steam temperature, increased vibration, abnormal axial displacement, and water hammering sound ； deal with: Immediately break the vacuum emergency stop. 28. Reasons for vaporization of feed water pump - low deaerator pressure, low water level, blocked inlet filter, too high water temperature, insufficient pump inlet pressure. 29. The role of turbine cranking is to prevent the rotor from bending after shutdown, check dynamic and static friction before starting, and check the oil system of the top shaft. 30. Steam turbine cold start-up parameters - main steam pressure/temperature meets the regulations, vacuum ≥-85kPa, oil temperature is normal, and hydrophobicity is turned on. 3. Electrical Major (12 questions) 31. Electrical "Five Preventions" lock-up content - to prevent accidental opening and closing of circuit breakers, load closing of isolating switches, live hanging ground wires, ground wire closing switches, and mistaken entry into live intervals. 32. Generator air inlet/outlet temperature standards - inlet air: ≤40℃ ； show off: ≤65℃ (different units have slight differences). 33. The hazards of motor phase loss operation - sharp increase in current, overheating and burning of windings, decrease in torque, fluctuation in speed, and protection actions. 34. Treatment of light gas operation in transformer - check oil level, oil temperature, leakage, gas color, take gas test, and stop operation for inspection if necessary. 35. Danger of positive/negative grounding in DC system - positive grounding: May cause protection malfunction ； Negative ground: May cause protection to refuse to move. 36. Hazards caused by ferromagnetic resonance of voltage transformers - overvoltage, burned out transformers, blown fuses, and malfunctioning protection. 37. Advantages of double-blade moving contact of high-voltage isolating switch - increase contact area, improve heat dissipation, enhance electric stability, and prevent misoperation. 38. Non-all-phase operation definition and protection - three-phase circuit breaker does not close/open at the same time ； Protect: Zero sequence protection and negative sequence protection can avoid non-total phases. 39. Allowable temperature value of motor bearings - sliding bearings: ≤80℃ ； rolling bearing: ≤95℃. 40. The purpose of rapid switching of factory power is to ensure continuous power supply to the factory, prevent auxiliary machines from tripping, and ensure the safety of the unit. 41. How lightning arresters protect electrical equipment - breakdown discharge during overvoltage, limiting the voltage below the equipment insulation level, protecting the equipment. 42. The function of synchronized locking circuit - prevents non-synchronous parallelism, system impact and equipment damage. 4. Thermal control and comprehensive management (8 questions) 43. Each function of PID - Proportion (P): Quick response ； Points (I): Eliminate static difference ； Differential(D): Advance adjustment. 44. How a thermocouple works - The temperature difference between two different metals generates a thermoelectric potential to measure temperature. 45. If the temperature of the differential pressure flowmeter is not compensated, it will be too high, and the display will be - the density will decrease as the temperature increases. If it is not compensated, the flow will be shown to be small. 46. Contents of “Two Votes and Three Systems” – Two Votes: work ticket, operation ticket ； three systems: Shift handover, patrol inspection, and regular test rotation of equipment. 47. Principles of emergency response for all-round attendants - protect people, the power grid, and equipment, make quick judgments, operate correctly, and report in a timely manner. 48. How to deal with colleagues who violate rules - stop, correct, and report to leaders immediately to prevent illegal work. 49. What situations need to be reported to the duty leader immediately - major equipment failures, safety accidents, personal injuries, parameter limit violations, and protective actions. 50. Low-load operation challenges of the unit (boiler power) - boiler: Combustion is unstable, hydropower is poor, heating surface is over-temperature, and denitrification exits. - steam turbine: Vibration, high discharge temperature, large expansion difference. - electric: The power consumption of the factory fluctuates and the output of auxiliary engines is limited.