Elements of Electrical Engineering- I

  1. Discuss the Iron Losses of the D.C. Generator.
  2. A long-shunt dynamo running at 1000 r.p.m. supplies 22 kW at a terminal voltage of 220 V. The resistances of armature, shunt field and the series field are 0.05 Ω, 110 Ohm and 0.06 Ω respectively. The overall efficiency of the above load is 88%, Find:
    • (a) Cu losses
    • (b) Iron and friction losses
    • (c) torque exerted by the prime mover.
  3. Discuss the principle of D.C. motor.
  4. Discuss the different types of characteristics of D.C. generator.
  5. A 25-kW, 250-V, D.C. shunt generator has armature and field resistances of 0.06 Ω and 100 Ω respectively. Determine the total armature power developed when working
    • (i) as a generator delivering 25kW output
    • (ii) as a motor taking 25kW input.
  6. Discuss,
    • (i) Ta/Ia characteristics of D.C. series and shunt motor
    • (ii) N /Ia characteristics of D.C. series and shunt motor.
  7. The armature winding of a 4-pole, 250 V D.C. shunt motor is lap connected. There are 120 slots, each slot containing 8 conductors. The flux per pole is 20 mWb and current taken by motor is 25 A. The resistance of armature and field circuit are 0.1 Ω and 125 Ω respectively. If the rotational losses amount to be 810 W find.
    • (i) Gross torque
    • (ii) useful torque and
    • (iii) efficiency.
  8. Write principle of operation of a transformer.
  9. Discuss and draw phasor diagrams of transformer when it is loaded with different types of loads.
  10. The parameters of a 2300/230 V. 50-Hz transformer are given below:
    • R1 = 0.286 Ω, R2‘ = 0.319 Ω, R0 = 250 Ω , X1 = 0.73 Ω, X2‘ = 0.73 Ω, X0 = 1250 Ω
    • The secondary load impedance ZL = 0.387 + j 0.29. Solve the exact equivalent circuit with normal voltage across primary.
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