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Recent content by subtech

  1. subtech

    Delta Connected CTs

    The currents flow as they would in any Delta connected circuit. The return path for line current Ia would be through line Ib and Ic. If you ask questions, others may think of you as foolish or ignorant. If you never ask questions, you will remain foolish and ignorant.
  2. subtech

    Impacts of Series Capacitors

    David Is there sufficient compensation to cause the faulted line angle to be less than 30 deg?
  3. subtech

    Relay Protection

    oldfieldguy is on the right track. I have dealt with this problem many times. While it is true that many e/m relays have two taps on the target/S.I. unit,(.2 & 2A ?) lockout relays by design are very fast and they require little current to operate. Hence, the current that operates the target...
  4. subtech

    Strange currents / phase angles at co-gen site

    I'm not trying to over-simplify, but your numbers look to me like you've a cap (or two) stuck on C phase. Remember that even if the phase currents are equal, but the angles differ significantly from the normal 120 deg, you will have neutral current. Overall, your pf may be near 1, but with the...
  5. subtech

    Tap changer oil samplig

    Different gases occur for different reasons. The rapidly elevated Ethane, Methane, and Ethylene numbers signal something very hot in the compartment. Normally operating circuit breakers (and tap changers) generate very little if any Ethane, Methane, or Ethylene.
  6. subtech

    Tap changer oil samplig

    Most troubling are the Ethane, Methane, and Ethylene numbers. These are "heating gases", or more accurately stated, over heating gases. Something in the TC is getting very hot. Also of concern is the Hydrogen. This occurs with partial discharge or low level "corona". Was the "changed" oil new...
  7. subtech

    Aluminum Pipe Bus splitting

    Along with the water, you can expect animal inhabitants as well. Animals bring debris of all sorts. As soon as possible, I would inspect the bus for a buildup of debris which can hold not only moisture, but corrosive contaminants. Another point to consider is mechanical stresses caused by...
  8. subtech

    Disturbance recorder in new systems

    We have had very good service from the Areva/Bitronics M571/M871 series units. They are very versatile. Each unit has trending, DFR(2), and disturbance recorders(2) and lots of memory.(up to 128 MB). Ethernet,RS485, RS232 (com ports are configurable and totally independent) Modbus on one, DNP...
  9. subtech

    How to test SEL 121G

    A simple sign in procedure at the SEL website will provide you with access to not only a user manual for the 121, but a wealth of related info as well.. www.selinc.com
  10. subtech

    Florida blackout

    Probably not an FPL guy for much longer...
  11. subtech

    Florida blackout

    Defeating protection on a hot, humid day with higher than normal load? Somebody better have their story figured out really, really well.....
  12. subtech

    Personal Email prohibited at work

    My employer has rules about phone, email, and internet use while I'm on the clock being paid. Personal business of any kind is not allowed at any time, for any reason. I follow the rules. Always (only exception is sick, injured, or dead relative) I have personal rules about phone, email...
  13. subtech

    Grounding for CTÆs/PTs in LTC controller scheme.

    1. No, I wouldn't. We use Beckwith controllers and have several circulating current/paralleling schemes in use. Our practice is to supply 1 grounded conductor from one transformer control cabinet, and carry that conductor to all other points (such as the a and b contacts from the main and bus...
  14. subtech

    Bridge Collapse in MN

    The vibration/resonance idea is interesting. I believe it is important to remember that buildings and structures of most any shape/size can have many resonant frequencies. I once found that a rather large gymnasium had three acoustically resonant frequencies using a signal gererator, a rather...
  15. subtech

    Oxygen in Transformer oil

    Agree with oldfieldguy. Additionally, O2 occurs as a result of the aging and degradation of paper insulation. If the transformer is of relatively recent manufacture (6-10 yrs.) your oil may contain an O2 inhibitor which in effect "absorbs" oxygen and keeps the numbers relatively low. As the...
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