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  1. pwrtran

    Understanding delta VT ratios

    waross - in this case the open corner delta windings are built in, it will not be completely missing phase in this open corner delta even the primary has one phase missing.
  2. pwrtran

    Phase-GND(N) Voltage fault (Urgent)

    Measure voltage between L2 phase on swgr A and swgr B you will confirm whether L2 on swgr B is grounded or not!
  3. pwrtran

    Understanding delta VT ratios

    Veritas, you brought a very interesting discussion, thank you! By the way, I call it open corner delta, to me it is more clear on the concept. Well, missing one healthy phase under unfaulted balanced conditions is different than single phase fault conditions. If just sum two phase VT secondary...
  4. pwrtran

    Delta Inverter ( Source ) to a TT Grid

    Any type of transformer can be use as the utility-DG interconnection transformer. Grounded Wye as the primary on utility side cause desensitize L-G protection if the utility source is weak. Delta on utility side will cause TOV concern on unfaulted phases. Either high current contribution or...
  5. pwrtran

    CT Misconnection

    My thought is this: It depends on the secondary burdens. CTs are transformers but special ones. Let us assume two extreme cases: 1) B and C secondary windings are open (of course induced high voltage, but let us park it aside) - no secondary current, open circuit voltage is Vc +(-Vb) = Vcb<90°...
  6. pwrtran

    a small currents at one end shield earthed appear and may punch in weak end to flashover breakdown

    Transformer is inductive and the your cable in capacitive, I was wondering if it reached a "sweet" point of resonance! Another thing is the poor workmanship on the cable terminations, it happens quite often!
  7. pwrtran

    Insulating gravel vs coarse subgrade gravel

    You need to have a specification. Other than the resistivity test you may consider aggregates gradation test either by the quarry or by a third party. There are always some smalls and fines, the gradation test will confirm whether the test samples meet your specification. Specify clear crushed...
  8. pwrtran

    Would an isolation transformer eliminate a large voltage on the neutral?

    Isolation transformer will not fix your problem. The voltage difference between the hot and the neutral matters only, while the difference between the hot or neutral to a third reference point is relative. If your V(L-N) is applied to the isolation transformer varies, the secondary voltage...
  9. pwrtran

    Would an isolation transformer eliminate a large voltage on the neutral?

    Do you mean ungrounded system has a neutral wire brought out to customer location? Ungrounded system is mostly for industrial 3-phase load customers not a very good practice for single phase load customers. A Delta-Wye transformer should be installed at the demarcation to create a new system...
  10. pwrtran

    Electricity from Railway Tracks

    cranky108 and waross hit the nail. It is traditional railway signalling system before the digital world. There are many zones to sectionalize the tracks, and low voltage DC is applied to the tracks. A small leakage current is measured when When no train is passing the zone or section, a large...
  11. pwrtran

    Wiring heaters on Y connections from a delta source

    Dracula7, the heater nameplate rating information voltage and wattage wise, it may provide you the answer you are looking for. For example the heater could be single phase type but the designer wanted to gang them and connect them wye? Or perhaps the designer wanted to indicate heaters are not...
  12. pwrtran

    Wiring heaters on Y connections from a delta source

    Hi Dracula7, you are correct that 277 is the phase to neutral voltage. 480 is the phase-phase voltage and the relationship is root 3, 1.732. So 480/1.732=277VAC.
  13. pwrtran

    connecting protection relay of power transformer

    Technically you can but is not a good practice if there is another option. In our case we have two different protections sharing the same CT circuit. But make sure the CT was rated for your application and the burdens are okay and be aware that you will lose the diversity.
  14. pwrtran

    Transformer Percent Impedance with 120 vs 240V Dual-Voltage Outputs

    Hi prc, I couldn't agree that the impedance will not change. I don't have transformer manufacturing experience but ABB Transformer Handbook, Page 3-23 and 24, gives calculation of reactance, it is based on the geometric dimensions and the number of turns of the winding.
  15. pwrtran

    Transformer Percent Impedance with 120 vs 240V Dual-Voltage Outputs

    Hello prc, the impedance is dominated by the structure of the transformer. In this case, the primary winding structure is not changed but the secondary winding will be changed depending on the parallel or series connection. So I think the impedance will not be the same. A simple way to find...
  16. pwrtran

    Transformer Percent Impedance with 120 vs 240V Dual-Voltage Outputs

    I was scratching my head - is it possible "Percent Imp (2) 2.8" should be read as "Percent Imp (Z) 2.8". Letter "Z" instead of 2?
  17. pwrtran

    Insulation of bus bars at 35 kV

    Many insulated busbars are not fully rated insulation but insulation to prevent single phase fault migrates to a more damaging 3 phase fault due to the arcing and metal dust contamination released during a fault.
  18. pwrtran

    Is it possible? &quot;Leftover capacitance&quot; after a power outage to power a breaker trip coil?

    If it is a prolonged total station outage the battery bank could be discharged. Use a battery eliminator type charger will help to get control power back right after the AC is restored.
  19. pwrtran

    SCADA Monitored Interlocking System

    Hi all, does anybody know if there is a scada monitored interlocking system available on the market that can replace the mechanical kirk key interlock? Thanks!
  20. pwrtran

    Causes of humming sound in a transmission line (below 220 KV) other than corona effect

    If it is not corona it might be some mechanical vibration around 60Hz

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