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A severe high surge (due to short ckt in one of our outgoing bay) came 1 year before leading to total black out & tripping of all 5 connected units in our power plant. Ours unit is 300 MW Chinese made DongFang unit. That day we were not able to give Barring gear and turbine (coupled with Generator) kept on standstill condition for 90 minutes. Then turbine was put on barring gear. Now when Turbine was put back on service, till rolling on 3000rpm (ours 50 hz grid) no vibration was there (5th & 6th shaft vibration. 5th & 6th are Generator bearing). Shaft vib on 5th & 6th were 50 um.
Now after during synchronization when excitation was closed the Generator Shaft vib (5th and 6th) went up to 110 & 100 um. As we increase load the vib wnt up till 180 um (250 um is the trip value) But Turbine HP-LP Shaft vib is normal. Since then our Excitation system & AVR (Automatic Voltage Regulator) was kept in Manual Mode so as to minimise the excitation current. One observation is: At 250 MW ,Rotor vibration (5th & 6th) was 150 um. When Load decreased to 150 MW (Keeping Excitation Current Constant in Manual Mode), shaft vib went up to 200um (May b due to As reactive power is inversely proportional to MW). Regular Impedance tests at different speed were conducted but no such faulty valy. Static RSO was satisfactory.
Now management is thinking for Dynamic RSO and Flux probe test (Air gap mag fld wave detection). Does the inability to give barring gear resulted in a probable rotor Sag thats leads to uneven distorted mag flux? or a rotor hot deformation factor is there with excitation heating of rotor causing rotor bending (as rotor may be deformed by the hugh surge on that very day)?
Please give me necessary help as i am in the charge of this Generator.
Now after during synchronization when excitation was closed the Generator Shaft vib (5th and 6th) went up to 110 & 100 um. As we increase load the vib wnt up till 180 um (250 um is the trip value) But Turbine HP-LP Shaft vib is normal. Since then our Excitation system & AVR (Automatic Voltage Regulator) was kept in Manual Mode so as to minimise the excitation current. One observation is: At 250 MW ,Rotor vibration (5th & 6th) was 150 um. When Load decreased to 150 MW (Keeping Excitation Current Constant in Manual Mode), shaft vib went up to 200um (May b due to As reactive power is inversely proportional to MW). Regular Impedance tests at different speed were conducted but no such faulty valy. Static RSO was satisfactory.
Now management is thinking for Dynamic RSO and Flux probe test (Air gap mag fld wave detection). Does the inability to give barring gear resulted in a probable rotor Sag thats leads to uneven distorted mag flux? or a rotor hot deformation factor is there with excitation heating of rotor causing rotor bending (as rotor may be deformed by the hugh surge on that very day)?
Please give me necessary help as i am in the charge of this Generator.