Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Search results for query: *

  1. brainsalad

    Fault impedance - resistive or reactive?

    Hello, I am inserting fault impedance into 3-phase and line-to-line faults in order to find a limiting condition for overcurrent and undervoltage relay coordination. This is for industrial 4.16kV and 480V systems, which have a fairly high X/R ratio. Since the system is mostly reactive...
  2. brainsalad

    TCC plot reference voltage

    Hello, Suppose I have a 3-phase 480V panel which has 277V branch positions. Is it correct that the TCC plot reference voltage should be 480V? I am trying to plot a branch circuit breaker and am unsure if it should be 277V or 480V. Will a single pole single phase breaker off of such a panel see...
  3. brainsalad

    Sizing of control power transformer fuses for degraded voltage conditions

    Hello, Suppose in a plant that the voltage at an MCC is below normal due to a degraded switchyard voltage. Fed from the MCC are various motors which use size 1, 2 and 3 starters. With a degraded MCC voltage, the contactors are expected to draw more current due to a degraded source voltage. For...
  4. brainsalad

    Dual-element fuse derating for temperature

    ...of the fuse)? For example, my fuse is graphically made of a bunch of (Amp, time) points, and for 140F, I have a ~70% derating on time and an ~87% derating on current-carrying capacity, so to derate I should take my set of Amp, time points as (0.87*Amp, 0.7*time). Thanks for your thoughts.
  5. brainsalad

    Simplified method for estimating the acceleration time of centrifugal drives

    ...been many helpful posts on motor acceleration time on eng-tips, but none which I have found which might explain why: average motor torque, Tm = (3*Tlr + Tbdn)/4 (Tlr = locked-rotor torque, Tbdn = breakdown torque) average load torque, Tl = Tl/3 Can you explain how these averages are...
  6. brainsalad

    Plotting undervoltage and overcurrent relays on same amps base

    Attached are two pages from the paper to help clarify the problem - this shows one method of performing UV vs. OC coordination...Thanks for your thoughts.http://files.engineering.com/getfile.aspx?folder=16ac17a3-178b-4f9d-a5da-eb57a1f9770f&file=Archive_2.zip
  7. brainsalad

    Plotting undervoltage and overcurrent relays on same amps base

    Thanks mgtrp. The undervoltage relays are only supposed to transfer the source when there is truly a loss of voltage situation, not when there is a dip from a phase fault. So I'm in the process of coordinating these devices...
  8. brainsalad

    Plotting undervoltage and overcurrent relays on same amps base

    smallgreek: thanks for your response. I am coordinating incoming feeder phase overcurrent relays with 4.16kV bus undervoltage (loss of voltage) relaying.
  9. brainsalad

    Plotting undervoltage and overcurrent relays on same amps base

    Greetings: Wondering if anyone can share more examples or experiences with coordinating undervoltage and overcurrent relays. The paper "Allowing for decrement and fault voltage in industrial relaying", Arnold Kelly Industry and General Applications, IEEE Transactions on Date of Publication...
  10. brainsalad

    Undervoltage relays: working backwards to find fault current from relay pickup?

    Hello, If I had an undervoltage relay in a 120V relay loop receiving input from 4.16kV bus 4200/120 PT's, would it be appropriate to apply symmetrical components to determine, given the relay pickup (say 55V/120V) and the system sequence impedances, a fault current which would depress the bus...
  11. brainsalad

    overcurrent and undervoltage relay coordination

    Pwrtran: thanks for your inquiry, however I am just interested to know what others general methodology is for coordinating overcurrent and undervoltage relay operation.
  12. brainsalad

    overcurrent and undervoltage relay coordination

    Greetings: Wondering if anyone can share their thoughts on (4.16kV/480V) overcurrent and undervoltage relay coordination. A range of fault currents (three-phase,line-to-ground,line-to-line,line-line-ground) and corresponding post-fault bus voltages could be calculated and compared to the UV...
  13. brainsalad

    Effect of neutral reactance on transient overvoltages (high resistance grounding)

    Greetings: Attached is a picture of the zero sequence network of a solid ground fault with high resistance grounding (from EPRI "Grounding and Lighting Protection") Practically speaking, if the resistor/xfmr was connected to the neutral through a long cable (say 5kV, 2/0, 200'), would its...
  14. brainsalad

    High Resistance Grounding: Neutral conductor contribution to 3-phase charging current?

    pwrtran: thanks for your response. The generator is neutral grounded through a high resistance scheme (through a distribution transformer, 10 kVA, 4160/240V, with 4.2ohm on the secondary.). My main question was: given that the components which determine Xco (the 3-phase capacitive reactance)...
  15. brainsalad

    High Resistance Grounding: Neutral conductor contribution to 3-phase charging current?

    Hello, to refresh and add a new thought: when the generator is first powered, couldn't the neutral conductor shunt capacitance become charged before the Vng becomes zero? Thanks for your thoughts.
  16. brainsalad

    High Resistance Grounding: Neutral conductor contribution to 3-phase charging current?

    Greetings: The generator neutral conductor of a HR grounded system is rated 5kV, 1/C, #2/0, 100'. In totaling the system capacitance, how can it reasoned to include the shunt capacitance of the neutral conductor? Under balanced operation, the voltage across the neutral should be zero, which...
  17. brainsalad

    Dunki's sqrt(3)*rated voltage motor life rule of thumb

    waross: Apologies the statement is now corrected per rcwilson - thanks both. electricpete: how cool, thanks, I think that answers the question!
  18. brainsalad

    Dunki's sqrt(3)*rated voltage motor life rule of thumb

    Greetings: Can anyone familiar with the following rule of thumb, "one hour of operation at sqrt(3) times rated voltage equates to about 700 h of operation at unity (rated) voltage" from "The Reality of High Resistance Grounding", Dunki-Jacobs, IEEE Trans. On Industrial Applications, Vol...
  19. brainsalad

    As-built generator high resistance neutral grounding issue

    odlanor: Thanks very much that was the correct guide indeed. To refresh: Neutral current I_r is less than 3*I_c (i.e, resistor kW < system charging kVA, X_cg/R_n is less than 1.0) in an as-built system. From IEEE C62.92.1989 it can be seen that transient overvoltages will exceed 250% (lost...
  20. brainsalad

    Control power transformer - Secondary's view of primary's short circuit

    Thanks for your thoughts. To show that the actual secondary fault current (as "seen" through the fuse) through a 480/120V, 150VA, Z = 3.5%, control power transformer, while considering the 10,000A available fault amps (at the primary), does the following make sense? Using secondary as base...

Part and Inventory Search

Back
Top