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  • Users: HienN
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  1. HienN

    3.5 MW motor starting problems continue...

    I am the one who still confuse what is you really want. 1. For the switchgear: Normally, the control power is VDC or 110VAC fed from the external source. For example, the UPS, which is energized from another transformer, let's say, even your factory use medium voltage for big motor. It also...
  2. HienN

    3.5 MW motor starting problems continue...

    I think this case will depend on the type of Breaker you intend to use (Motorized or mechanical). As a matter of fact that the 02 cases will use a typical "Tripping circuit", where the trip coil is energized via external signals (via reset, emergency, or via protection relays contacts...). The...
  3. HienN

    3.5 MW motor starting problems continue...

    LionelHuzt: It could be understood. However, I think, just base on the safety aspect. The main coil as well as protection relays shall be energized from the external sources (like batteries or UPS). So, there will be time to cut off the main contacts during the short circuit problem. For...
  4. HienN

    Sizing transformer

    Rafiq Bulsara, Many thanks to you for the valuable supports. I will do it myself. Regards,
  5. HienN

    Sizing transformer

    Thank you for all of your useful posts. I confirmed that the base capacity of 110/22kV Transformer is 40MVA. Z% is at 13 percent. The next step is how to calculated the short capacity at the source? Is that SC capacity at the source is ~300MVA? When sizing the transforme capacity, why we...
  6. HienN

    3000A Ground Fault Protection breaker tripping

    Could you post the diagram up here. We should see the diagram.
  7. HienN

    3.5 MW motor starting problems continue...

    Ters: Some more words, for big motors (hundreds of kW up), "starting regime" is required by manufacturer. (Like 01 hot, 02 cold…) For example, it can only be restarted after several minutes for cooling down (cooling the motors down only). At the same time, power fuses could also have time to...
  8. HienN

    Aluminum Conductor Steel Reinforced (ACSR)

    I think the most important thing is us. Regards
  9. HienN

    3.5 MW motor starting problems continue...

    Not only overcurrent protection. it should better be added with Short circuit (instantaneous) current protection. In this case, we can eliminate the power fuses. For most of contactor switching, equipped with fuses may be standardized. The manufacturer offers you fused compartment as an option...
  10. HienN

    Sizing transformer

    Thank you, If I dont ask, it may lead me to many misunderstading in actual application. By the way, what is the difference between the base and forced cooling capacity? If this 63MVA is forced cooling capacity then I would ask for the base? Moreover, at the same time with this, for 110/22kV...
  11. HienN

    3.5 MW motor starting problems continue...

    I like Oldnotbold post. Gave him a star.
  12. HienN

    Sizing transformer

    But I was wrong, the impedance is not that small. It should be around 12 to 14% for 63MVA transformer. With this impedance, the short circuit current will reduce dramatically.
  13. HienN

    Sizing transformer

    Rafiq Bulsara, Utility company transformer is 63MVA capacity with 8% PU. Overhead line distance is about 1.5km.
  14. HienN

    3.5 MW motor starting problems continue...

    Electricpete: I agree with you for this case. I did mean by saying that all large motors need fuses. But would like add up by saying a little bit more that: For big motors (Medium voltage motors) that use contactor as switching equipment. Fused vacuum contactor is the cheapest one in...
  15. HienN

    Sizing transformer

    Marmite:I did some calculation for transformer 110/22kV and found that the short-circuit current at the 22kV size would have been around 23.6kA. Then, consulted some other Vendor like Schneider (local), and knew that it was not that high (just around 10~16kA). Not satisfied yet, I switched back...
  16. HienN

    3.5 MW motor starting problems continue...

    Some more words, considering of eliminating the power fuses, this practice should be very careful. Fuse is natural protection device while relays are only mechanical and electronic one. Hence, the malfunction, mis-coordination, and damage could occur on such equipments. Extra protection by power...
  17. HienN

    PT100 VS TC

    Dear friends, If I want to measure the signal from PT100 and PT50 sensors, how is the measuring unit? It will be measured by Calibrator. And for thermal couple? Is its signal in Volt? Regards, HienN
  18. HienN

    Sizing transformer

    Rbulsara, Normally, the short circuit current available at the outlet of 110/22kV transformer (belong to Power company) in our location is limited at 25kA (already contacted). Can we utilize this information to apply to short circuit capacity of the inlet of our 22/6.6kV transformer. As I said...
  19. HienN

    Sizing transformer

    Rafiq Bulsara, Thanks for your first opening, For software, I have been using ETAP400. But it seems so difficult to understand while information is sitll not enough. For the voltage drop, as reference to the last project, the voltage drop during starting is within 5 to 10% at the 22/6.6kV...
  20. HienN

    Aluminum Conductor Steel Reinforced (ACSR)

    Hi 7anoter4, Thank you for your effort, I have tried this book "Transmission and Distribution Electrical engineering" issued by News 07’ edition. Please refer to the attachment for more details. Anyone knows where does this information coma from? It seems that bringing me back to the old time...

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