Common reasons for condensing steam turbine failures

Generally, turbo-generators are not prone to failure under the correct use and maintenance, but if they are improperly used and maintained, the environment is poor, and they are in disrepair for a long time, they will also cause failures.

Condensing steam turbine common failures reasons

Generally, the reasons for common failures should be analyzed as follows:

1. The generator output voltage is unstable

(1) For AVR control (normal for manual control), please refer to the AVR manual;

(2) In manual or automatic control, there may be other mechanical reasons in the system or the speed of the prime mover is unstable;

2. The output voltage is too high, check whether the voltage reading meets the AVR requirements, refer to the AVR manual.

3. Generator excitation fault

(1) If the excitation is normal in manual control but not in AVR control, please refer to the AVR manual and check the connection;

(2) There is no excitation current during manual control or automatic control, check the circuit between the AC exciter, the rotating rectifier and the AVR, and check whether the lead wire of the rotor coil is open circuit;

4. The generator vibrates greatly

(1) Electrical aspects: short circuit or grounding between turns of the rotor coil, uneven air gap, deformation and displacement of the rotor coil, damage and looseness of the stator core insulation;

(2) Mechanical aspects: the rotor is unbalanced, the center of the generator is not properly matched with the steam turbine, the gap between the bushing and the rotating shaft is uneven, the oil is lacking or the bearing fixing screws are loose, the foundation is not firm, etc.

5. Axial series movement of generator rotor

(1) The rotor position is inclined when the generator is installed;

(2) The center of the stator and the center of the rotor do not coincide when the generator is running.

6. Damage to the stator core

(1) When the stator coil breaks down, the silicon steel sheet is burned;

(2) The iron core is loose due to poor manufacturing or rusted iron core.

7. Failure of the stator coil

(1) The looseness of the slot wedge or the end pad causes the winding insulation wear;

(2) Insulation aging caused by overheating of stator winding due to overload or other reasons;

(3) Mechanical damage to winding insulation caused by sudden short circuit;

(4) Winding insulation breakdown due to overvoltage;

(5) Insulation damage caused by relaxation of stator core;

(6) Poor welding of stator coil joints.

8. Failure of the rotor coil

(1) Insulation resistance drop due to the accumulation of dirt at the end of the rotor coil;

(2) The sudden unloading of the generator causes the overspeed of the unit to increase the excitation voltage, which exceeds the rotor voltage of the generator and causes insulation breakdown;

(3) Short circuit between turns of rotor coil or unstable grounding;

(4) Partial overheating of the rotor due to unbalanced load or asynchronous operation;

(5) The generator overload causes excessive excitation current and overheating;

(6) Poor contact of coil joints causes overheating and insulation aging.

9. Failure of bearings

(1) Due to the poor insulation between the bearing bush and the shaft, the shaft current passes through the bearing, causing the bearing to overheat and corrode;

(2) The bearing is overheated due to insufficient oil and other reasons;

(3) Bearing oil leakage caused by improper oil adjustment and poor sealing;

(4) The center of the bearing is not aligned, and the bearing bush is scratched.

10. Failure of the cooler

(1) Blockage of cooler pipes due to cooling water fouling;

(2) Due to the mechanical damage, corrosion and vibration of the pipe, the expansion port leaks and the pipe ruptures;

(3) Condensation of water droplets on the surface of the cooler is caused due to the low temperature of the cooling water or the inflow of air with too much humidity from the outside;

(4) Because the inlet water temperature of the cooler is too high, the inlet water volume is too small, or the hot and cold air ducts are short-circuited, the outlet air temperature of the cooler is too high;

(5) The gaskets between the water chamber and the bearing plate are aging and not tight with each other.

11. Overheating of the generator

(1) Generator overload operation;

(2) The iron core or winding is short-circuited;

(3) Malfunction of air cooler or ventilation system.