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  1. inpran

    Transformer Differential Protection

    Just to add on to the previous replies, during a fault on one phase, the harmonic blocking settings(settings mostly in percentage - ratio of harmonics to the fundamental component)will take care of the case. The general settings I have come across is 15% for second harmonics(I2/I1 - I2 is...
  2. inpran

    Online DGA: Manufacturers

    I have come across Calisto and A-eberle make online DGA monitoring devices in different projects. We had both integrated to SCADA (relays were specifically ordered with the 61850 protocol) and did not have much issue during integration of both of them. Data collection was fully remote.
  3. inpran

    YnDyn0 vs Dzno, advantages and disadvantages

    prc, a three winding transformer is being replaced by a 2 winding one. YNyn0d (the vector group for delta winding is not mentioned by slavag)is being replaced by a DZn0. Correct me if I am wrong here please, zig-zag transformers are not used for loading purpose. At least I have never come across...
  4. inpran

    132kV Transmission line induction - pre-commissioning tests

    acog, if you are trying to gauge the healthiness of a line via 5 kV Megger, then, as mentioned by Marmite, it is futile. I have used offline fault locator before commissioning of lines for checking line healthiness and diagnosis. (you can google for "offline fault locator") There is no safe...
  5. inpran

    VT connection

    P1lts, then only R phase voltage will not be there for you in the secondary. Y - B phase volatge will read 110 V, Y - R will read 63.5 V and B - R will read 63.5 V.
  6. inpran

    CT saturation in a high impedance scheme

    @cesgibis: 1. For an internal fault, as pointed by you "When an internal fault occurs in a high impedance differential protection (whether REF or bus bar),the voltage across the relay can reach high levels" The fault current will enter the high impedance circuit resulting in raise in...
  7. inpran

    Transformer Temp Trip

    There are thermal overload protection for that. Not that the idea of tripping transformer on high windning temperature is uncommon.
  8. inpran

    Auto reclosure

    Wangi, Its 79.
  9. inpran

    Same 87T for 2 transformer not paralleled

    odlanor, If yours is a numerical relay, the second energisation, ergo the inrush current that follows the second energisation should be restrained by the internal algorithm of the differential function block in the relay. So, even if you energise the two transformers sequentially, it shouldn't...
  10. inpran

    Are there usually two trip coils on medium voltage power circuit breakers?

    bdn2004, The 2nd trip coil is indeed redundant. As has already pointed out in this thread, both the trip coils will activate the same trip latch. If your system /specifications don't need this redundancy, you can parallel all your trip commands to the same trip coil.
  11. inpran

    Are there usually two trip coils on medium voltage power circuit breakers?

    bdn2004, Could you please clarify few things. You have two trip coils in your oil circuit breaker. One of it is for protection tripping and manual tripping. The 2nd one is for emergency cases. The new piece of equipment you now have two tripping contacts, one that makes whenever your...
  12. inpran

    Bushing CT Grounds

    We carry out insulation resistance check with voltage levels mentioned by prc for secondary to ground. But have not carried out between primary and secondary.
  13. inpran

    OLTC - On Load Tap Changer

    Linspire, OLTC will have its own surge relay and pressure relief device. Transformer will have a separate pressure relief device. So the protection will be two separate and independent entities.
  14. inpran

    Test winding in Bushing current transformer

    prc, Yes, that is the usual practise followed in reactors/transformers provided with a test point. But I'm yet to come across a case where there is more than one turn test winding. The rating of these points, as pointed by Phovnanian, depends on the manufacturer and application I suppose. The...
  15. inpran

    Transformer tripping on Standby Earth Fault (SEF) protection if neutral of transformer is grounded.

    kssr, Please share more info as to what is the rating of the transformer? What is the application? When the Transformer trips on SEF, is there a fault observed on any other feeders/bays in your sub-station? Do you have the settings for the relay available and can you upload the Disturbance...
  16. inpran

    CT Selection for Restricted Earth Fault protection

    Babambu, It is not an issue if you are using a low impedence protection for REF.
  17. inpran

    OLTC go through mid position

    Sisi29, Drive Unit. I had a similar problem an year back. It was just a case of a wire coming out lose in one of the contactors. Check the schematics in the Drive unit.
  18. inpran

    When is a transmission line too short for distance protection?

    Veritas, When there is a fault in the line, your distance element will still be active even when your communications are down. This element will in turn trip the breaker at local end. However, I have come across relays that will block the primary protection, distance or differential, when...
  19. inpran

    When is a transmission line too short for distance protection?

    Veritas, If communications fail, you still trip the breaker at your end and ensure that the fault is not being fed from your end. If the fault persists, and there is a relay at the remote end, then the remote end breaker too will trip. The communication is in place just to ensure that the remote...
  20. inpran

    Hi-Z REF Protection!

    Yeruk123, The calculation what you have given holds good when the resistance of both the CTs are same. However due to different resistances there are possibility of circulating current in theory. In practice however , you will still observe zero current. But to be on the safer side...

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