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    EC question of 2015 semester five


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    A dc shunt generator has an induced voltage on open circuit of 127v. When the machine is on load, the voltage is 120v. Calculate the load current, if the field resistance is 15ohm and armature resistance is .02ohm. Neglect the armature reactance.
  • Answers

    2 Answers found.
  • Let us assume that no load voltage is Eg, load voltage is V, load current is I, shunt current is Is, current through armature is Ia and armature resistance is Ra.

    The equation governing the current and voltages in shunt generator is -

    V = Eg - IaRa
    and Ia = I + Is

    using them we get -

    120 = 127 - Ia*0.02
    so Ia = 350 ampere
    and load current I = 120/15 = 8 ampere

    Knowledge is power.

  • Let us assume the following,

    E = Voltage
    E1 = Voltage at No Load = 127V
    E2 = Voltage at Load = 120V
    Ia = Armature Current
    I = Load Current
    Rsh = Field Resistance = 150 Ohms
    Ra = Armature resistance = 0.02 Ohms

    Now,
    Ia = Net Voltage / Resistance
    Ia = (E1 - E2) / Ra
    = (127 - 120) / 0.02
    = 7 / 0.02
    = 350 Amp

    E = Eb + IaRa
    or, Eb = E - IaRa

    I = E / Ra
    = 120 / 15
    = 8 Amp

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