cristhmart
Electrical
- Nov 7, 2004
- 4
Hi! We have a 3.5 MW, 4.16 kV, 4 poles synchronous generator with brushless rotor refurbished recently by substitution of the four poles for original replacement parts. We put the unit in parallel service with another identical one delivering 1.6 MW at 0.8 pf each one. The vibration analysis reveals a very smooth operation during the first 40 minutes of parallel operation from cold start and then a suddenly strong vibration and sound force to trip the main breaker and the steam turbine. Most electrical parameters were recorded including phase currents, phase voltages, phase power factors and none of them present any variation until the main circuit breaker is trip.
Two adjacent poles jut out 12 mils respect to the other ones in radial direction and the refurbished rotor has 1/8” less of overall diameter than the original one. The two journal bearings are mounted on the generator frame and concentricity of the rotor related to the stator was verified giving a 5/16” uniform air gap.
Stator traces show a physical contact with the rotor like right half of stator fixing bolts were loose and, in fact, the weld was found broken. No damage on the babbits.
Because the retaining rings of the first rotor opened out (most probably for a main exciter ground leakage found and no loose of field protection present) almost everyone suspect of the rotor again and the generator remains out of service.
The machine owns to a small budget sugar mill which has only 112 days per year harvest running yet.
I suggest welding of the fixing bolts but everyone is afraid that most severe damage could arise from unexpected fault of the rotor or stator. I have no doubt about the right electrical behavior of the machine but I wonder if I’m missing something in the thermal behavior of the joint. Could someone give me any advice? If I have a bad interpretation of the electrical facts or I missing something about the rotor or stator issues, please feel free to tell me. Are the fears of the people ok? What tests would you suggest before running the unit?
Two adjacent poles jut out 12 mils respect to the other ones in radial direction and the refurbished rotor has 1/8” less of overall diameter than the original one. The two journal bearings are mounted on the generator frame and concentricity of the rotor related to the stator was verified giving a 5/16” uniform air gap.
Stator traces show a physical contact with the rotor like right half of stator fixing bolts were loose and, in fact, the weld was found broken. No damage on the babbits.
Because the retaining rings of the first rotor opened out (most probably for a main exciter ground leakage found and no loose of field protection present) almost everyone suspect of the rotor again and the generator remains out of service.
The machine owns to a small budget sugar mill which has only 112 days per year harvest running yet.
I suggest welding of the fixing bolts but everyone is afraid that most severe damage could arise from unexpected fault of the rotor or stator. I have no doubt about the right electrical behavior of the machine but I wonder if I’m missing something in the thermal behavior of the joint. Could someone give me any advice? If I have a bad interpretation of the electrical facts or I missing something about the rotor or stator issues, please feel free to tell me. Are the fears of the people ok? What tests would you suggest before running the unit?
