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Recent content by akm

  1. akm

    CANIRT help TO DETECT SUBSURFACE UTILITY MAINS ?

    We have a situation in a parking lot of rectangular size of 300,000 sqft, and we need to locate the utility mmains underground at 5-6 ft. It is known that there are electrical duct bank under a concrete vault some 5 feet below, and a few 4 inches water PVC pipe carrying ambient water. It is also...
  2. akm

    Useful life expectancy

    When you give examples of panelboards, switchboards, circuit breakers, motor control centers, transformers, I assume you are mostly worried about the insulation health, and of course the ageing of metal parts due to making and breaking also. To address the first and important part(Insulation)...
  3. akm

    use of delta-wye distribution transformer in step up mode

    Since Saturday last, we have taken a shut down and the 9 years old cable installation upstream is being physically examined. So far, we detected the following. Primary winding(208 side) connection brazing is pitted, insulation burnt to brittle pieces, metallic connection rigidity is almost...
  4. akm

    use of delta-wye distribution transformer in step up mode

    stevenal: I admire your brief conclusion.
  5. akm

    use of delta-wye distribution transformer in step up mode

    To my surprise and all your excellent analytical suggestion; The results are here: At grounded neutral: upstrem phase to phase voltages, 212,212,213, delta side opencircuit voltage 476,467,481 At open/floating netral: phase to phase voltages, 192,208, 18, neutral shift(voltage between float...
  6. akm

    use of delta-wye distribution transformer in step up mode

    Electricpete: Your wrap up may be correct,as I doubt we may have a fault in the 208 side connection of the transformer, raceway and associated cable connection. This does not answer the single question that we have: how could this faulty one pump power through the step up transformer to a 70~...
  7. akm

    use of delta-wye distribution transformer in step up mode

    I measured the open circuit voltage at 480 side in floating neutral mode (as thought to be a viable solution), measurements are 480/470/27. (load at 480 completely isolated-please note). X0-system neutral measurement, possibly high shift could not be measured today out of panic results, will do...
  8. akm

    use of delta-wye distribution transformer in step up mode

    Stevenal and busbar, per your advise, I did the floating neutral situation as explained above and ended up at 476, 453 and 27 volt at delta 480 v side of trafo. Waiting for your any other investigational tips and solution.
  9. akm

    use of delta-wye distribution transformer in step up mode

    We have run this unit with the said step up transformer for 5 months, with a few trippings on overload, remained stray events for us, untill recently the units tripped immediately on start. We contacted the trafo manufaturer and told them that the step down trafo is used as a step up, and we...
  10. akm

    use of delta-wye distribution transformer in step up mode

    1)The trips are on overcurrent, due to both unit starting, since this is the only programmed mode/manual mode of starting of the freeze 7 thaw unit, we have been told by the manufacturer. 2) The measured undervoltage is immediate upon strating the unit. 3) On supply side, the voltage dip is down...
  11. akm

    use of delta-wye distribution transformer in step up mode

    both the compressors are started simultaneously, impedance is 4.5%, We have run the unit in this condition for 5 months until recently, it started tripping on overload.
  12. akm

    use of delta-wye distribution transformer in step up mode

    Busbar's word of caution is appreciated. Please advise me, if I have to go for a 208(wye)/480(delta) step up transformer, 225 kva for two dedicated compressors load of 30+30 hp,why is the compressors tripping on huge undervoltage. The step up transformer output voltage is unbalanced and goes...
  13. akm

    use of delta-wye distribution transformer in step up mode

    Would like to get some concrete answer to the doubts. I have gone thru the said reference. Am constrained to use a transformer which is 225 kva, 480/208, DyN, in a step up mode to get 480 volt connection fot this load. I repeat my specific doubt>> Do I hv top float the neutral in the supply 208...
  14. akm

    use of delta-wye distribution transformer in step up mode

    Would like to get some operational tips, if I need to connect a delta-wye-n(480/208) transformer in step up mode. connect to supply source of three phase line(208) from utility source and run a cyclic load of compressors at 480 volts fro the delta 480 v side. Do I need to isolate the netral on...
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