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  • Users: timm33333
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  1. timm33333

    Insulation Coordination

    I have a question regarding insulation coordination. The conventional insulation coordination study involves hand calculations of protective margins (PRL1, PRL2, PRS) of surge arrester. However there is also frequency scans based insulation coordination study done by software, which involves...
  2. timm33333

    Sizing of Gas Turbine Generators

    I am trying to figure out the sizing criteria of large gas turbine generators (GTG) when non-linear loads are present. Information is easily available on the web for sizing the small diesel generators, but not much information is available for large gas turbine generators. For sizing the small...
  3. timm33333

    Transmission Line Clearance

    I am trying to figure out which rule of NESC addresses the horizontal clearance between 161kV transmission line and an industrial facility (like a well pump). NESC rules 233(B) and 234(B) talk about horizontal clearances, and 233-3 talks about clearance envelope, but these are not clear. Also...
  4. timm33333

    Soil Resistivity Measurement

    I have a question regarding the soil resistivity measurement. Soil resistivity for the ground grid system of high voltage (HV) substations is measured as per IEEE-81. How about transmission lines, is it required that the soil resistivity be measured at the base of each tower of high voltage...
  5. timm33333

    Power Control by Reactive Power of Shunt Reactor

    I am looking for the logic for the control of power system using the reactive power provided by 230kV shunt reactor. For example if the voltage is not within +/- 5%, then the taps of shunt reactor would be changed to bring the voltage within acceptable limits. Likewise if the current at the...
  6. timm33333

    HV Neutral Conductor

    I have a question about the voltage rating of neutral conductor for solidly grounded 230kV shunt reactor. NEC 250.184(A)(1) states that for solidly grounded systems greater than 1kV, the insulation of neutral conductor has to be minimum 600V. So for 230kV solidly grounded shunt reactor, the...
  7. timm33333

    Reactive Power Compensators

    I have a question about reactive power compensators (Static VAR Compensator, Static STATCOM, and Dynamic Synchronous Condenser). Are all of these used to improve the voltage drop at the receiving end of transmission line? Also, do they provide capacitive-compensation or inductive-compensation...
  8. timm33333

    Medium Voltage Substation Yard

    I have couple of questions regarding a 34.5kV substation yard of an industrial facility, it contains a 34.5 kV outdoor switchgear and a 34.5kV outdoor oil type transformer. The substation is on the load side of the utility meter, so technically it is in the jurisdiction of NEC. Can we still...
  9. timm33333

    Medium Voltage Fault Interrupter

    I have a question about sizing of 25kV SF6 type fault-interrupter. It receives power from utility on the line side, and supplies power to a 12/16/20 MVA transformer on the load side. The available sizes of fault-interrupter are 600A and 900A. The maximum current on the transformer primary is...
  10. timm33333

    Arc Flash Analysis -- Energized Equipment

    I have a question about arc flash analysis. NEC 110.16 requires that labels are required for all equipment which is likely to be worked on while energized. The definition of energized equipment should come from the owner. But if owner does not provide this information, then how do we determine...
  11. timm33333

    Transformer Base Conversion

    Base change formulas are used to change the transformer-impedance from transformer-base to system-base. Can these formulas also be used to convert the impedance from one transformer base to another transformer base? For example for a 10 MVA 34.5kV-12.47kV transformer: the impedance is given to...
  12. timm33333

    Transformer Primary Fuse

    I have a question about sizing the primary fuse for 12.47kV-480V 3750 kVA transformer. The primary full load current would be 174A, and a 200A fuse would be required. For S&C SMU-20 fuses: 100E has a continuous current rating of about 200A, and 200E has a continuous current rating of about 500A...
  13. timm33333

    Arc Flash Questions

    I have a couple of questions regarding arc flash study as below: 1. In arc flash study when we assume that the main breaker of the MCC is isolated from the bus by a barrier, then should we print two labels for the MCC (first label for the cubicle which contains the main breaker, and the second...
  14. timm33333

    Arc Flash Calculations--Contribution From Utility

    I have a question about arc flash calculations. We calculate incident energy at the maximum and minimum values of fault currents provided by the utility. But in our case the utility only has the maximum value of fault current (minimum value of fault current is not available). So I will have to...
  15. timm33333

    Power Factor Correction and Harmonic Resonance

    I have a question about power factor and resonance. When all motors are without VFD’s (variable frequency drives) then the power factor is lagging, and we use capacitors to improve power factor. When some motors are without VFD’s and some motors are with VFD’s, the VFD’s would improve some power...
  16. timm33333

    Underground Raceway Calculations

    I am looking for a solved example which shows step by step calculations of underground cable ampacity using Neher McGrath method. The original Neher McGrath paper (published in 1957) has some examples, but these are not clear. NEC Annex B has tables, but it does not have example. Maybe IEEE-835...
  17. timm33333

    Out of Step Protection for Stability

    I am trying to figure out what would be the acceptable/recommended settings for the out of step (78) protection relay for generator. (For example for loss of excitation(40) protection of generator, the recommended diameter of MHO circle is Xd and the recommended offset of MHO circle is Xd’/2.)...
  18. timm33333

    Neutral Grounding Resistor IEC

    In NEMA, the minimum voltage at which NGR (neutral grounding resistor) is allowed is 480V. What is the minimum voltage in IEC at which NGR is allowed? Thanks.
  19. timm33333

    VT Accuracy

    In IEC there are separate accuracies for metering VT and relaying VT. For example IEC accuracy "3P" for relaying VT, and IEC accuracy of "0.5" for metering VT. In ANSI standards, the accuracy of metering VT is defined (for example ANSI accuracy "0.3W" of metering VT). But I cannot find the...
  20. timm33333

    Relays in Coordination Study

    I am trying to figure out whether it is required to include the differential relay in the coordination study. I heard that differential relay cannot be coordinated because it is instantaneous. Is it correct? Thanks.

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