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  • Users: BrkfldEE
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  1. BrkfldEE

    Open CT secondary causing high impedance in primary?

    In a high voltage substation there is an incoming source transmission line that connects to 2 circuit breakers, so the current from the incoming source splits between these 2 circuit breakers. One of these circuit breakers tripped due to a "pole discrepency", which means that one phase current...
  2. BrkfldEE

    using 2 taps on a multi-ratio CT

    Will using 2 different taps of a multi-ratio CT work? Will it cause any problems?
  3. BrkfldEE

    Fiber Optic Cable Service Loop

    Is there a Code Requirement to leave service loops for Fiber Optic Cable? I have heard and read lengths of anywhere from 10' to 100' but I do not see anything in the NEC that explicitly says that a service loop of any length is required. Does anyone know of one?
  4. BrkfldEE

    noise induced on non-shielded wires in cable

    I have a 125VDC control circuit that uses a non-shielded cable in a tray with AC power cables. There is 60 Volts AC being induced on a 125VDC wire. I know that the solution is to pull in a new shielded cable, but, does anyone know of a way to "drain off" this induced AC instead of pulling a new...
  5. BrkfldEE

    Standby battery bank discharge test

    We have standby battery banks to provide DC power for our generating stations. Recently we started a monthly discharge test where we turn off the battery charger for five minutes to test the capacity/condition of the batteries. There has been some conflicting ideas on whether this is a good...
  6. BrkfldEE

    field discharge resistor - small hydro generator

    I have a hydro generator that is 12.5MVA, 13.8KV. The rated field volts and amps are 250V, 240A; and according to my datasheet the field resistance is 0.904 ohms. The rotating exciter has nameplate info of: 80KW, 250V, 320A, shunt wound. I am removing a field breaker that is in the exciter field...
  7. BrkfldEE

    Sizing Temporary Protective Grounds

    thread238-82004 Does anyone have a clear method to size temporary protective grounds? I have read IEEE 1246 and that doesn't seem to go into enough detail. I have read IEEE 1048 and it references some tables in ASTM F855-1997. However I can only get access to ASTM F855-2009 which doesn't seem to...
  8. BrkfldEE

    battery short circuit current

    I am working on evaluating our battery banks for arc flash hazards. The battery manufacturer gives a short circuit current rating of the battery, for example 2,044Amps. My question is, if I have 23 cells do I have to multiply the short circuit current by 23?
  9. BrkfldEE

    5A CT secondary

    My system has a 1200:5A MR CT that is being used on the 800:5A tap. If the transformer was fully loaded at it's 2 stage forced cooling rating, the total CT secondary Amps would be 6. Is it ok to use a CT with a nominal current above the 5A rating?
  10. BrkfldEE

    sizing a three phase breaker for a single phase transformer

    I have a single phase 10kVA transformer that is fed from two phases of a 480V 3 phase supply. If I want to protect the transformer with a 3 phase circuit breaker, how should I size it? The full load amps of the single phase 10kVA transformer is 20. So do I use 20A as my basis for choosing the...
  11. BrkfldEE

    Generator Field Excitation Audible Noise

    I have a horizontal hydro unit, 3MVA, and when the excitation is applied to it, a screeching noise starts that is very loud and annoying. Does anybody know the reason for this? I have heard that it has something to do with the way the rotor was made?
  12. BrkfldEE

    CT rating

    I am try to specify current transformers for the protection of a 25MVA hydro generator. Can somebody help me understand what the CT ratings mean? C400? C800? T400?

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