MGVCL Exam Paper (30-07-2021 Shift 2)
A short-shunt dc compound generator supplies 50 A at 300 V. If the shunt field resistance, series field resistance and armature resistance are 30 Ω, 0.03Ω, and 0.05 Ω respectively, determine the e.m.f. generated.
Equivalent resistance of the circuit, Req = (12||18) + 8 Req = 7.2 + 8 Req = 15.2 ohm Source current = current through 8 ohm resistor, I = Vr/R8 I = 20/8 I = 2.5 A Supply votage V = I*Req V = 2.5*15.2 V = 38 V
Slip, s = (Ns - Nr)/Ns Ns = 120f/P 0.05 = (1000 - Nr)/1000 Nr = 950 rpm Speed of rotor with respect to stator magnetic field = 950 - 1000 = -50 rpm
Speed of the stator magnetic field with respect to stator core = 0 Speed of the rotor magnetic field with respect to rotor = sNs Speed of the stator magnetic field with respect to rotor magnetic field = 0 Speed of the rotor magnetic field with respect to stator core = Ns
EXAMIANS