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  1. ausphil

    CB Short time rating

    Operating CBs above their rating. It'll do it pretty quick, but only once. Ausphil
  2. ausphil

    [Please Help] Post installation test on MV cable

    A couple of points: 1 - IEC does specifiy the test voltage and time. It gives you the 3 options as above. 2 - the agreement is between the purchaser and contractor, the manufacturer may have nothing to do with the tests after installation. The wording under section 20.1 states that the test on...
  3. ausphil

    [Please Help] Post installation test on MV cable

    JuanBC, Unfortunately you can't make a call as to whether it has passed a test or not, as you don't have a known test specification that you can make a pass/fail decision on. 7anoter4 got part way there in specifying IEC 60502. However the test that your contractors have performed does not...
  4. ausphil

    Sticking?

    "stiction" in electromechanical relays? Relay maloperation can lead to loss of local control. In order to answer "what real is" you might need to go to philosophy-tips.com ausphil
  5. ausphil

    Oil Analysis - Equivalent TCG %

    IEEE C57.104 shows the equation in section 6.3 It is hard to reproduce in this forum. ausphil
  6. ausphil

    CT Misconnection

    waross, The metering diagram is slightly different to davidbeach's issue. The metering circuit doesn't have secondary windings in series, even though it sort of looks like it. What goes into the two meter elements in essentially the vector sum of B-A and C-B, so this doesn't put any of the 3...
  7. ausphil

    CT Misconnection

    davidbeach, that is a good question. my guess is that the current that ended up in B (and hence the negative value in C) would be a harmonic laden current that is not representative of either the original B or C phase primary current. As you suggest, the secondary would probably be driven...
  8. ausphil

    TR fire wall forces?

    Does anyone else see the irony of the 4.5kg fire extinguisher in the photo on page 6 of Power0020's attachment? Ausphil
  9. ausphil

    PD monitors for GIS on 230 kV

    At 132 kV, we purchase the GIS with the sensors fitted, check them at commissioning, then have the option to install a permanent monitor down the track, or perform periodic online PD checks with a handheld meter. I do recommend at least purchasing with the factory installed sensors, then if you...
  10. ausphil

    Delta Transformer Vector Group dashed "reference" line meaning?

    Arrehman1, The "dashed reference line" is drawn to represent an equivalent star winding (from the phase to an equivalent star point) when looking at a delta winding (HV or LV), so you can directly compare the HV to the LV side. It is not describing any actual winding in the transformer tank...
  11. ausphil

    Lead Wires sufficient for PD testing

    It depends on whether the lead is to be self insulated (as dpmac has given the example of), or if you are hanging them in the air from your test transformer to your equipment that you are testing, in which case they don't need to be insulated. In addition to insulated leads, for voltages up to...
  12. ausphil

    Altitude Correction Factor

    miltonboss, This altitude correction factor is based on the change in pressure with height. The correction factor that is applied is proportional to the ratio of the air pressure at sea level over the air pressure at elevated height (ie p0/p, as you are multiplying by Ka) It can roughly be...
  13. ausphil

    Subtransmission voltage regulation

    We run both those voltage ratings that you have used as examples, and have automatic on-load tapchangers on both of those voltage rating transformers. We also then run manually set off-load tapchangers for our 11 kV to 415 V transformers. If you were trying to run without on-load tapchangers...
  14. ausphil

    transformer testing

    Is your complete system, from generation to load, completely underground? If not (which is the most likely answer), then there is always a chance of a lightning strike on an overhead conductor, that will transfer its way into the cables that feed your transformer, hence it is completely valid...
  15. ausphil

    Earth continuity conductor

    Power0020, reason number one in your OP is essentially it. with a cross bonded system, your have a continuous conductor bonding the two earth systems, which is your sheath. Any through fault current will return in the sheath and provide a low impedance path back to the source. with a single...
  16. ausphil

    Calibration of Hi Pot Meters

    It is quite standard to use resistors and a voltmeter in a high voltage measurement system. The resistors bring the voltage that is applied to the voltmeter (or multimeter here) down into the range of the voltmeter, then the voltage displayed on the voltmeter is multiplied by the resistive...
  17. ausphil

    Touch shock at 345kV breaker control panel

    Is there an earth strap across from the cabinet to the door? If not, this could explain the feeling when touching the door and the padlock. Also, if there is one, check that it is continuous. The issue of not measuring any voltage may be because of the input impedance of the multimeter. If it...
  18. ausphil

    Forward and negative fault.

    johndaniel, This refers to the type of fault detected, and it is based on the voltages and currents that are present during the fault. Rather than trying to explain, if you paste this address into your searchbar, it will give you a pdf from Schweitzer on negative sequence relay operation...
  19. ausphil

    Using AC to test power cable

    VLFit, I apologise for citing standards that answered Relayman1000's original post, ie testing with power frequency. I thought that the VLF test requirements had been covered well by others, and I wanted to give Relayman1000 a reference for his initial line of questioning. Ausphil
  20. ausphil

    MV cable sheath testing

    Yes, we've found the oversheath test to be useless if it is in a plastic conduit. We did some tests to find out how good the graphite coating was. We found that after about 5-10 metres, this was useless to rely on if the cable wasn't laid in a nice earthed situation. The graphite layer is...

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