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  1. scottf

    On ferroresonance damping resistor

    If I'm reading your original post correctly, you should not have to provide external ferroresonance damping for CVTs. With VTs, one has to be concerned with system ferroresonance, therefore, an external damping strategy. With CVTs, there is a concern with internal ferroresonance, therefore...
  2. scottf

    Voltage given from the secondary of the capacitive voltage transformer

    If you're applying voltage to the CVT secondary, closing the potential ground switch (PGS) will short the intermediate transformer's primary winding and you will get high current in the transformer windings. To your original question, utility practice comes down to "is there 0% chance" versus...
  3. scottf

    PD TEST ANALYSIS

    There can be many causes and a lot more information would be needed just to hazard a guess.
  4. scottf

    Exceeding Metering Class CT Burden Rating

    Short answer: no One of the main problems is that you're mixing transient performance of a protection class CT with "steady-state" performance of a metering class CT. The accuracy of a metering class CT, is primarily a function of the % nominal current and the applied burden. All else held...
  5. scottf

    PT ratings on impedance grounded systems

    stevenal...the to neutral if connected line-to-neutral or to the other line if connected line-to-line. 2400/4160Y means the unit can be connected L-N on a 4160V system or l-l on a 2400V system.
  6. scottf

    PT ratings on impedance grounded systems

    Kiribanda- I don't believe you are correct You CAN use a 2400/4160Y V PT - which is a 2-bushing VT You CANNOT use a 2400/4160GY V PT - which is a 1-bushing VT The line-to-neutral voltage on an impedance grounded 4160V system is indeed 2400V.
  7. scottf

    PT ratings on impedance grounded systems

    1) The H2 bushing is rated to an insulation class and not a specific voltage. So the 5kV class would be 75kVp BIL and 26kV PFWV. 2) Yes, the VT can withstand temporary over-voltage. Normally marked as the Over-Voltage Factor (OVF) on the VT's nameplate. Typically, units of this design would...
  8. scottf

    Definition of Metering Accuracy for Rogowski Coil

    The accuracy rating would be measured value.
  9. scottf

    Definition of Metering Accuracy for Rogowski Coil

    My opinion is that type Rogowski coils would not be suitable for metering and certainly not revenue metering. The error defined for Rogowski coils is normally referring to the ratio error only. Phase angle error on Rogowski coils can be quite high...normally defined in degrees...0.5 to 1.0...
  10. scottf

    PT Ferroresonance vs Modern SEL relay

    Do you have the previous page available? Would like to see what it says leading into the paragraph at the top of the page you posted.
  11. scottf

    PT Ferroresonance vs Modern SEL relay

    I've never seen resistors placed in parallel with any kind of burden. The only thing I can think of is if the resistors are there in case the unit is energized with the relay isolated out of the circuit (Open test switch for example) and the resistors would be left to give the VT some load...
  12. scottf

    Current transformers- over voltage on open circuiting secondary

    I have certainly seen oil-filled CTs fail catastrophically due to prolonged secondary open-circuit. I think your statement about the secondary voltage going up about 20 times the burden voltage is not correct...or not totally correct. For an rms standpoint, yes, but the peak voltages developed...
  13. scottf

    Current transformers- over voltage on open circuiting secondary

    This question very much depends on the type of CT. LV, MV, or HV Bushing CT Dry-type MV Oil-filled HV Bottom line is that a CT left with an open secondary will fail in some manner given enough time. Often times, the initial failure will be at the secondary terminals, depending on the...
  14. scottf

    Bushing Current Transformer X, Y, Z Marking Practice

    From what I've seen, there is no standard practice here and you'll need to refer to the unit's nameplate to see the CT relative orientation.
  15. scottf

    1 Bushing vs 2 Bushing PT Required

    34500/34500 GRD Y is an odd-ball rating normally seen in switchgear applications where the VT is spec'd to be able to take the line-to-line voltage indefinitely, but is a single-bushing VT connected line-to-ground....so it's normally energized at 58% rated voltage. To my understanding it's rated...
  16. scottf

    Experience with Cast Epoxy Resin Instrument Transformer Catastrophic Failure (72kV)

    JPC- * Full disclosure - I work for an instrument transformer manufacturer that makes dry-type VTs up to 69kV and I'm not sure if the unit being discussed here is our unit or not. I looked in our quality system and don't see a record of this event being reported, so perhaps it is not our unit...
  17. scottf

    CCVT Spark Gap

    Cranky- In former times when we were in most aspects of carrier system (CCVTs, line traps, and line tuners) we would recommend that the carrier cable from the CVT to the line tuner be 5kV stranded cable and it be run on stand-off insulators. If run in conduit, it should be plastic and not...
  18. scottf

    CCVT Spark Gap

    How is the quality of the grounding at the station? In our experience these induced transients seem to happen in locations with poor grounding conditions/soul resistivity issues.
  19. scottf

    CCVT Spark Gap

    System Protection I understand your comments in grounding shield at both ends.The induced transients is a fairly rare issue and with the customers I know that have the issue, I believe they've had good success with grounding on both sides and I don't think they out in add parallel conductors...
  20. scottf

    CCVT Spark Gap

    Forgot he other bulletin....https://files.engineering.com/getfile.aspx?folder=eac07d1b-3ea7-4a2c-9616-bf17d4770ef3&file=Induced_Transient_Potential_(2019_06_11_13_23_01_UTC).PDF

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