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  1. powerzizo

    thyristor stack failure

    Hi All, we have four similar 360MW steam turbine generating units build in 2002, The generating units are equipped with static excitation system. The generator output voltage is controlled through automatic voltage regulator. The voltage regulator controls the output of 18 thyristors...
  2. powerzizo

    Onsite high voltage test for 420MVA

    Hello Everyone, We had just finalized onsite repair for 420MVA/18/220kV.The high voltage exit leads had been replaced due to poor crimping. Part of the repair scope is to conduct high voltage test by the repair company. What is the best practice in this case, should we hire third party to...
  3. powerzizo

    thread238-414004 Hello everyone,

    thread238-414004 Hello everyone, i refer to my last December 2016 thread regarding two identical transformers 420MVA repair due to the same defect, finally one of them was repaired by replacing high voltage exit leads which were found burnt. the transformer is back in operation after passing LV...
  4. powerzizo

    High DGA

    Thank you
  5. powerzizo

    High DGA

    Thank you prc, some photos for the repair to explain the poor crimping and uneven number of strands issues. DBDS in all transformers between 100 to 180 ppm-Oil corrosive test was positive, passivator content 35ppm and we will top up to 100ppm. IS there a standard procedure somewhere for the...
  6. powerzizo

    High DGA

    Thank you. Just to clarify,in which condition step a can be provided?and what level of voltage?
  7. powerzizo

    High DGA

    Hi All, Apology for late update. The transformer repair company has completed the replacement of HV leads to tap changer.according to them the root cause of burning the leads is uneven number of strands in each cable 7 and 14 in addition to poor crimping method. The trans tanked after repair and...
  8. powerzizo

    High DGA

    Hi ScottyUK and All. This modification can be done from the tap changer side during shutdown or we will need to drain the oil and do some works from inside the transformer?
  9. powerzizo

    High DGA

    Thank you again for all. The two faulty transformers were on the same site, the staff in charge could not confirm that passivator was added. Oil sample from faulty Transformer will be analyzed for corrosive sulfur and passivator content. Inspection by OEM for both transformer revealed burning...
  10. powerzizo

    High DGA

    Thank you. The two in service transformers had Irgmet passivator added before 7 years .the passivator content is being analyses every 6 months and still around 60ppm.However ,we are currently analyzing corrosive sulfur and waiting the results. The OEM is busy detanking the transformer to check...
  11. powerzizo

    High DGA

    Thank you all . i attached some photos for the first faulty transformer findings during inspection by OEM who recommended insitu repair after skidding out for 2 m to enable de-tanking.Root cause not yet identified by OEM. The second faulty transformer not yet inspected. DGA results by OEM two...
  12. powerzizo

    High DGA

    Hi All we have two identical generators transformers 420MVA(18/220kV). both transformers has almost the same service time 14 years and got high DGA and buchholz alarms one year in between. both transformers are currently under inspection by OEM and initial findings were burnt cable in phase -W-...
  13. powerzizo

    Vacuum problem during start-up

    regarding the sealing steam- higher steam flow than normal noticed during start up. it was strange to see the LP turbine exhaust temperature increasing to 60-70C just after charging the sealing steam header and starting the vacuum pumps. normally the LP exhaust temperature decreases with vacuum...
  14. powerzizo

    Vacuum problem during start-up

    The steam turbine had major overhaul in April 2015, where all seals were reviewed and tolerances checked-we had few start ups without vacuum problems. we are preparing for vacuum pumps capacity test this week.
  15. powerzizo

    Vacuum problem during start-up

    We are running a power station with two steam turbine units 360MW each. in which SEIMENS EMLO-F 2BE1 liquid ring vacuum pump installed two per each steam turbine unit. Normally with 2 pumps in service we are able to pull condenser vacuum from atm to 130mbara in 70 minutes. We had a problem last...

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