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  1. NormGA

    EMF Question

    Years ago I assisted my young daughter with a science fair project titled: EMF's: Higher in your home or near power lines? After making many, many readings with a Gaussmeter we determined that the magnetic field levels were much higher in the average home than near power lines or substations...
  2. NormGA

    Testing Phase Angle Relationship for Transformer Differential Relay

    If you are talking about verifying the current input to your protective relays I suggest that a better way would be to use a phase angle meter in conjunction with an ammeter. That's the way I've been doing it for the last 30 years or so. The high side current connected in wye with low side in...
  3. NormGA

    Two LTCs paralleled û one runs to 16L & other 16R - what will happen?

    I am assuming that the low side bus was carrying load while the readings above were made, then: It appears to me that the polarity of your Watts reading on LT1 is reversed. If Watts is reversed, what about vars? Note that by assuming the negative MW readings are really positive, the real...
  4. NormGA

    Two LTCs paralleled û one runs to 16L & other 16R - what will happen?

    I have seen exactly this situation caused when an auxiliary switch contact in one of the LTC's kept it from running, while the control on the other unit continued to see low voltage. Each LTC had its own control and there was no paralleling protection. The transformers ran this way for over an...
  5. NormGA

    240V single phase supply

    Years ago we had to supply 120/240 single phase to a construction trailer on a site where the only other voltages we had were 46 kv and 277/480. We connected a readily available 7200-277 volt transformer to the 277, then a 7200-120/240 to the output. Worked well for a couple of years. Norm
  6. NormGA

    I have a problem that we are facing

    What are the phase angles of the currents? Norm
  7. NormGA

    Megger Testing In-Service CT or PT secondary winding

    Correct me if I am wrong, but aren't most if not all, CT's used at higher voltages shielded? The majority of my experience has been with higher voltage oil circuit breakers and I know that the current transformers are actually around the grounded portion of the bushing. On the 230 and 115 kv...
  8. NormGA

    Megger Testing In-Service CT or PT secondary winding

    I have done high voltage (I usually used 1000 volts) megger tests of many, many current transformer circuits while in service. These include power circuit breaker line relaying currents from 12 kv to 230 kv, metering circuits at same voltages, bus differential circuits and bank differential...
  9. NormGA

    System Voltage Phasing Measurements

    Are all these transformers in the same yard? If not, has line phasing been checked and rechecked? To me it appears that they are not in the same substation yard and are separated by some distance and the line phasing is not actually what it appears to be. In my company I have seen many older...
  10. NormGA

    Maloperation of auto-reclosing feeder CB

    Are your circuit breakers tripped by internal battery, external battery, or capacitor trip device? The problem you describe sounds like what happens when the tripping energy is supplied by capacitor trip device and you have an instant reclose on the breaker. Reclosing must be delayed long...
  11. NormGA

    Explosion of surge arresters

    It's most likely an active gap arrester you're talking about, and not an mov. Over time some of the series spark gaps fail, and at some point the entire spark gap assembly passes enough current to rapidly heat the silicon carbide blocks. The result is quite often an explosive failure. If this...
  12. NormGA

    Maximum current and KV per phase calculations.

    Assuming you are talking about a 3 phase system, the kva per phase is the total divided by three. So for your 1 kva transformer, the rating would be 333.3 voltamps per phase. To get the current, divide the voltamps per phase by the voltage per phase. Voltage per phase for your example is 415...
  13. NormGA

    Island Utility HV Capacitor Reactive Compensation

    If your voltage increases as much as 4 to 8 percent I would think you are putting on too many capacitors at one time. I don't think the inrush inductors have much to do with it, since their purpose is to limit the current inrush on energizing. As a rule, anything over a 5% increase in voltage...
  14. NormGA

    Island Utility HV Capacitor Reactive Compensation

    Are you talking about a temporary transient such as harmonics that you often get when switching capacitors or a jump in RMS voltage that is unacceptable? If the RMS voltage is going too high the size of the cap bank is too great for the size of the transformer and other system variables. It...
  15. NormGA

    Differential relay CT grounding

    Yes, that is an excellent way to determine the condition of your cables, relays, terminal blocks, internal panel wiring, and CT's. I have done this many, many, times and it has been scary every time, even though I open trip paths and trip cutout switches. The most common problem I encountered...
  16. NormGA

    Power factor correction???

    Convert each to rectangular form and add, then change back to polar. I get 12.9 A at 0.73 pf.
  17. NormGA

    Relay Usage?

    This sounds like a good application for a small PLC. Go to the PLC forum791 and post the same question. You can also go to Automationdirect.com and see what they have. http://store2.automationdirect.com/cgi-bin/ncommerce3/ExecMacro/plcdirect/homeframe.d2w/report
  18. NormGA

    Bus layout with delta wye transformers

    When facing the transformer low side, connecting high side phases in the sequence ABC, BCA, or CAB will all produce the same low side STANDARD phasor with counterclockwise rotation. The phases just come out on different bushings. However, by connecting the transformer in any other sequence...
  19. NormGA

    Three winding transformer commissioning test sheet

    Vector group and voltage ratios are easily determined with a Turns Ratio Tester, such as those manufactured by Biddle. The voltage used by the TTR is only about 10 volts. You should be able to determine who built the transformer by checking bushing nameplates, transformer prints, purchase...
  20. NormGA

    Do you purge the air from draw lead bushings?

    Why don't you ask the transformer manufacturer? Quite often a transformer of that size comes with a field tech to supervise the installation. But apparently not this time. But if you don't check with the manufacturer and a bushing fails they could try to balk on the warranty.

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