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About Insaf

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    Electrical Engineer

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  1. Insaf

    Pass Rate

    Where did you see?
  2. Irrespective of phases (1-phase or 3-phase), Sqrt(3) should not be part of the equation; answer will be 9 microF. Without investigating, many of us always use sqrt(3) for three phase system, but not the case always like this. In this case, phase to phase or line voltage already accounted, so don't need to use sqrt(3). We can examine the problem, based on 1-phase basis; Kvar required=150/3=50 and line to neutral voltage 208/1.732=120 V. Now Xc=120^2/-50=-288 ohm. Finaly C= (-1)/(2*pi*60*288)=9.1 micro Farad. In conclusion, original calculation considered line to line voltage and 3-phase kvar required for correction whereis 1-phase calculation accounted line to neutral volatgee and kavr required for single phase; both give the same capacitor value. There is no room for sqrt(3). Thanks,
  3. Insaf

    NEC problem

    article 110 is for "equipment" not conductors - - Article 490 also for equipment (Equipment, over 600 volts, nominal).
  4. Insaf

    NEC problem

    I don't see any clearance distance 15" in 110. Would you please specify the sub-number of article (e.g. 110.xx)?
  5. Insaf

    NEC problem

    Because the problem asks for minimum distance. Both 15" and 18" are minimum distances for BIL 150 (kV)and 200 (kV) respectively.
  6. I am struggling to get good reference materials on "Devices and Power Electronic Circuits". Any thought / advice will be appreciated. Thanks
  7. Insaf

    new NCEES #113

    ----------------------------------------------------------------------------- Because, neutral will have one direction for positive half cycle and opposite direction for negative half cycle. Please note that Load (RLoad) current direction will note change (always same direction). Thanks
  8. 114. Simply inverter will supply power to motor and it maximum voltage (value) will be Vdc which is 679 V. Here transistor is nothing but switch. 115. Current waveform is given, so integrating between staring point to end point ( 45 deg & 180 deg) and diving by time ( or in terms of radian angle) will give average value or DC value. Half cycle is enough because other half is symmetrical. 113. This link may be helpful: Thanks,
  9. If wye-connected source is grounded, is there any difference to determine VBG? Thanks,
  10. Insaf

    NCEES #111

    In practice, when power is supplied to a load, connection arrangement may not known. It can be treated as you are supplying power to a black box, so questions of wye or delta have no importance anymore. In that case any connection arrangement can be solved as Y connection considering a virtual neutral point (n point of NCEES solution). Then multiplication of phase to neutral value by 1.732 will give line to line value. So NCEES solution is correct (and less time consumimg)
  11. Insaf

    NCEES #111

    When they convert the load voltage VAB to Van, what relationship causes it to be shifted by -30 degrees? ---------------------------------------------------------------------------------------------------------------------------------------------------- In balanced three phase system Van, Vbn, Vcn are 120 degree apart from each other. Suppose we like to have phase relationship between Vab and Van: Vab= Van+Vnb= Van - Vbn; If we draw geometrically, we will see that Vab is leading Van by 30 degree. If we consider a numerical example, Van=1<0 deg, Vbn= 1<-120 then Vab= 1.732<30 deg = 1.73* 1<30 degree. Please note that delta connection can be solved in same way as Y connection, considering a virtual neutral point. Bottom line is that irrespective of delta or wye, phase voltage always lag line voltage by 30 degree.
  12. Insaf

    NCEES #518

    "Power Electronics by Muhammad H. Rashid" and "Power Electronics by Ned Mohan" are good sources of reference materials. Thanks
  13. Insaf

    NCEES #518

    VAve/dc= [3*Sqrt(3)/pi]*Vm (by integration) = [3*Sqrt(3)/pi]*(sqrt(2)(Vrms)); Here Vrms for line to neutral = [3*Sqrt(2)/pi]*(sqrt(3)(Vrms)) =1.35 VLL Note: Ques 518 (battery charger) is not related to this relation rather concern with Vmax. Thanks
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