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  1. Kiribanda

    Phase-earth fault in YNd11 step-up transformer while operating at no load

    Could you please share with the members, 1) SLD of the protective relay scheme of the transformer? 2) Which relay has operated? 3) Its settings?
  2. Kiribanda

    Step-up transformer = Star-grounded LV / Star-grounded HV. How to calculate EPR?

    What you say is correct. If the 415V system is totally with cables, yes the earth fault currents will go through the cable amour etc and the fault current discharged to the earth is very small meaning you are taking the split factor as almost zero. Unless I see the detailed dwg of the earthing...
  3. Kiribanda

    Step-up transformer = Star-grounded LV / Star-grounded HV. How to calculate EPR?

    You have mentioned that that two earthing systems are bonded together. No worries. That means any earth fault current on the 415V side will rise the EPR at the 11kV side too. Therefore, you have to consider 20kA earth fault current which is maximum out of the two values and calculate the EPR. If...
  4. Kiribanda

    FAT : zero sequence impedance measurement test

    For a YNd11 3-limb core transformer the zero seq. impedance is, 1) Between 0.7 to 1.0 of the positive seq. impedance when measured from the Y side. 2) Infinity when measured from the delta side. The test is performed at the Y side by connecting to a single phase source. This is a standard test.
  5. Kiribanda

    Delta Winding with grounding transformer on utility sub-transmission & distribution

    Having a DELTA on the 26kV or 12.47kV distribution system is little odd because, 1) when that system is connected to a customer he will definitely have a DELTA winding in his 26kV or 12.47kV side. That means the distribution system will become a DELTA/ DELTA ungrounded system. 2) The...
  6. Kiribanda

    Distance Relay on ETAP

    Best thing is to contact ETAP HELP. But you should have a current maintenance agreement with ETAP for any tech help. And also I believe that ETAP V16 is now outdated.
  7. Kiribanda

    25.3 kV Nominal Rating GCB Applied to 26 kV Nominal Validation

    1) Per IEEE C37 for nominal system voltage of 25kV the maximum voltage of the CB should be 27kV where max. voltage is for which the CB is designed for. Therefore, if the quoted CB is designed, manufactured & tested for C37 then the CB rating plate should show the "Rated Max. Voltage" =27kV. I...
  8. Kiribanda

    Zigzag earthig transformer+ NGR on the secondary side of a 132/33 kV Yd transformer.

    1) How much earth fault current that you are going to limit on the 33kV system? 2) Can't you use only a NGR to achieve that current without a ZIGZAG? 3) What is your main reason for specifying a ZIGZAG? 4)What is your SLD of your 33kV system?
  9. Kiribanda

    Upgrading Utility Distribution Transformer with an NGR

    System growth can happen by adding new generators at the upstream. As result the ultimate ground fault level (also 3-Ph) given today may be different after 10yrs time depending on the system growth.
  10. Kiribanda

    Upgrading Utility Distribution Transformer with an NGR

    Typically, not like phase faults, all line to ground fault currents on any distribution system are limited by the fault resistance. Therefore when you introduce an NGR then those GF currents are further limited and might go undetected. Therefore, unless a GF monitoring system is introduced it is...
  11. Kiribanda

    Offshore power transformer YNd1 vs YNd11

    Looking into the SLD followings are my findings. 1) I have seen that in NORTH AMERICA the winding configuration is always Dyn1 whereas in the other side of the world following IEC standards the winding is mostly Dyn11. A solid reason is not known yet to me. The change can be made by reversing...
  12. Kiribanda

    Fault Current Analysis

    What is the MVA rating of the Yndyn transformer directly connected to the Utility bus?
  13. Kiribanda

    "Zero offset" in tranformer's inrush current

    Herivelto, The non-zero happens due to high DC off set meaning very high X/R ratio. Depending on the transformer design meaning its X/R ratio, it may happen. If we are going to break the current during the short in-rush duration, then the non-existence of current zeros may be a problem for the...
  14. Kiribanda

    Short Circuit Calculation - Impedance Method - Three Winding Power Transformer

    Why you need to calculate? It is very strange to know why you cannot find the name plate of such a large critical transformer operating at 400kV?
  15. Kiribanda

    CONNECTING PE TO CLEAN EARTHSYSTEM

    CLEAN EARTH was an old idea when the manufacturers were not able to explain some erratic behavior of process control units. It is no longer valid now. Bond them together to make an equipotential. Also by separating them 5m in the soli do you think that it is possible to stop influencing the other?
  16. Kiribanda

    Overvoltage During Earth Fault

    I have no further comments until I see the transformer connections (vector group) at the other end of all feeders H01 to H06 feeders which I have already requested from newelecteng by my post on 28 Sep
  17. Kiribanda

    PT ratings on impedance grounded systems

    1)Yes, you are correct. It is 2400V to ground. Therefore, no questions. You cannot use a 2400/4160Y PT on an impedance grounded system. Instead you have to use DUAL bushing, 5kV class, indoor or outdoor with a VTR=35 if your secondary system is 120V AC. Therefore, rated primary accuracy...
  18. Kiribanda

    Overvoltage During Earth Fault

    beyond86 Yes, but does it mean that the 33kV system has got 643A as charging current? How do you account for that? Before I make any further comments I am curious to know, 1) Is the 33kV system a real "DELTA" system? 2) Does the 33kV system really needs an earthing transformer? 3) If yes, how...
  19. Kiribanda

    Overvoltage During Earth Fault

    beyond86, Yes I noted it. See the feeder relay results. Io_calc =643.458(A) meaning 3I0=1929Amps is the earth fault current. How do you justify that amount of large earth fault current if the 33kV side is DELTA? If the 33kV system is really a DELTA bus then there is only the charging current...
  20. Kiribanda

    Overvoltage During Earth Fault

    newelecteng: I noted the following. From the incomer relay, I Found that U0=14407.808(V)=14.4kV Per your SLD the incomer is solidly grounded. Therefore,U0 cannot be 14.4kV. It should read 76kV. Per SLD there is no VT at the 132kV side. Any comments?

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