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  • Users: bdn2004
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  1. bdn2004

    Analyzing a 3-phase fault recorded waveform from an SEL relay on a 15kV feeder breaker, when did the breaker trip, why is VB at 0V before the fault ?

    There was fault on this feeder breaker. The instantaneous relay was set at 18000 amps. There was no load on the feeder. Was the wave decaying on it's own then it tripped ? Or is the last part of the top current wave when the breaker tripped ? Another question is ... WHY is VB at 0V before the...
  2. bdn2004

    What is the %Z of this grounding transformer given this nameplate data ?

    Below is the picture of the nameplate.... as you can see Z0 = 97.14 ohms per phase. Or can this be figured out from this info ? If so what is the calculation ?
  3. bdn2004

    Asking for help making sense of a grounding transformer

    Below is a part of an EasyPower model showing a grounding transformer at the first switchgear coming off the large 100 MVA transformer that feeds this Plant. The grounding transformer is 500 kVA, 15kV Wye impedance grounded - 480 delta. Z= 4.87 ohms. It has a 29 ohm resistor, 300A, 10 sec...
  4. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    A new installation is being put into this Plant that is a copy of another just like it: as described.... (2) 300 kW rectifiers feeding the power to multiple crane rails. The rectifier vendor is not recommending this saying: "You cannot connect two of these rectifiers’ outputs in parallel. They...
  5. bdn2004

    Anyone have experience with Schneider SAG fighter? how do you calculate the short circuit value of the output ?

    A customer is installing these SAG Fighters in front of panelboards. The question is how do we model this in EasyPower power software ? From the literature it's a Dynamic Voltage Restorer...
  6. bdn2004

    Elevated cable trays - when could these be considered subject to physical damage and unsupported tray cable not allowed per the NEC?

    A guy at an established site (not new construction) got up in a mechanical lift doing some retrofit work, that goes on continuously at this site. Many of the tray cables coming out of the elevated cable trays have only strain relief at the tray then onto their conduit that extends up from the...
  7. bdn2004

    Does this panel need to be re-wired and the grounds and neutrals separated ?

    A 200 Amp overhead service feeds an outdoor 200A fused disconnect on the outside of the house. Circa about 1960. 3 - #3/0 wires in metal conduit go from that disconnect, through the crawlspace 50', to a 200 Amp panel board in the middle of the house. The conduit is bonded with a short piece of...
  8. bdn2004

    What happens when two sources are paralleled into one bus and the 15kV voltages are off by 400V ?

    We are trying to do a hot switchover of this 15kV bus that is fed from two different sources. I've tried to model it with EasyPower software. According to the software there is a 400V difference between the one system and the other. Is there a problem doing this?
  9. bdn2004

    Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

    We have a 150 kVA dry type transformer that is a part of a bigger packaged unit. That question came up. The transformer case will be bonded, there will be equipment grounding conductors run between the panel feeding it and the transformer. Looking at the NEC 250.4 ... it doesn't appear this is...
  10. bdn2004

    Does IEC = IAC in protective relay curves ?

    Basler provided printouts of their relay settings for new relays that replaced old ones in some old switchgear. They specified E2 - IAC Extremely Inverse. EasyPower does not have that pick. It has: E2 - Extremely Inverse and C1 - IEC Extremely Inverse. Note they specified IAC ... which isn't...
  11. bdn2004

    SEL-351S CT Saturation Protection can someone explain simply ?

    On a recent project an old 15 kV fused switchgear was replaced by new switchgear that uses HV vacuum circuit breakers and SEL-351S relays on the feeders that land on step-down transformers. Looking at the curves for the new feeder relays vs old E-rated fusing … the instantaneous setting for the...
  12. bdn2004

    138kV Short Circuit Utility data received looks like absurdly high numbers - explanations ?

    The Utility says the available short circuit energy is 6964 MVA at 138kV at their substation. The 3-phase fault value from the Utility is 29.38kA. 6,964,000,000 / (138,000 * 1.732) = 29,136 Amps ...close to the value given. I'm not used to dealing with transmission voltage levels, but doesn't...
  13. bdn2004

    Resistors in series with tripping coils in 125VDC power circuit breaker control schemes. WHY ?

    Have been asked to make modifications to the existing 125VDC hard-wired control system at an industrial plant. Below is a portion of that control. It looks like the Amber light drops the voltage to less than the threshold voltage of the control relay that's in series with it. Should an alarm...
  14. bdn2004

    Can dirty input power trip small thermal magnetic circuit breakers ?

    A new rectifier system is installed on an existing unit substation as the simplified sketch shows below. The 45A thermal magnetic circuit breakers that feed the small rectifiers trip shortly after the system is powered up. They heat up to 150 degrees F per infrared testing. We measured the THD...
  15. bdn2004

    Surge Protective Device at the point of service connected through a branch bkr, overcurrent req'd ?

    Looking at a proposed electrical design....they've got an SPD connected right at the new switchboard through a branch circuit breaker. I'm thinking perhaps this just for disconnection means.... but they used a #6 wire on a 100A trip. #6 is too small for a 100A circuit breaker normally. But if...
  16. bdn2004

    General question about customer owned transformer HV protection

    We have a small project to perform a power study for a new waste water facility. In the project documents they are specifying a new 750 kVA, 12.47-480V pad mounted, oil filled transformer. But they are NOT specifying new fuses in the HV terminal cabinet of that transformer. Is this the standard...
  17. bdn2004

    Replacing E-Rated Fused Switch with a HV bkr feeding a xfmr, is Ground Fault Protection Not Reqd?

    There is an existing overhead utility line that feeds a 12.47kV-480V, Delta-Wye 2500 kVA transformer that has E-rated fuses at the primary of the transformer. For reliability they are changing this feeder out and running underground cable directly from the Utility's switchgear to a new 12.47kV...
  18. bdn2004

    Electrode gap used in Arc Flash calculations....where does this info come from ?

    Does anyone have a chart or something to back up where this info comes from ? For example... On a 480V bus the selection in EasyPower is either 25mm (.984 inches) or 32mm (1-1/4") On a 34.5 kV bus the electrode gap is defaulted to 254 mm (10 inches) This effects the calculation.
  19. bdn2004

    Is there an issue supplying a 3-phase 4-wire service AND a 3-wire service from the same xfmr?

    At present this building (originally built as a warehouse) is fed by two services. One is 480/277V three phase 4-wire which mostly feeds lighting panels and the utility loads for the building itself. The other is a large 480V, three phase 3-wire service that was added when the building was...
  20. bdn2004

    Can you convert a 3-wire service to a 4-wire service calling the Equipment Ground the NEUTRAL ?

    Below is a sketch of a service from a Customer owned 12.47kV-480V transformer. There exists another service that comes into this same building that feeds the 277V lighting loads. That total load is no more than 200Amps, 480V, 3-phase. This is being re-worked so that there is only one service...

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