Basic Electronics and Electrical Engineering: Chapter 2: DC Machines
DC Machines: Exercise Problems
DC Generators and Motors
Basic Electronics and Electrical Engineering: Chapter 2: DC Machines (DC Generators and Motors) : DC Machines: Exercise Problems
DC Machines (DC Generators and Motors)
EXERCISE
PROBLEMS
1. A separately exited
generator running at 1500 rpm, supplies 250 A at 125V to a circuit of constant
resistance. What will the current be when the speed is dropped to 1200 rpm with
the field current unaltered? The armature resistance is 0.05 Ω and the total
drop at the brushes is 1.5 V. Ignore armature reaction. [Ans: 195.82 A]
2. A shunt machine,
connected to a 200 V mains, has an armature resistance (including brushes) of
0.15 Ω, and the resistance of the field circuit is 100 Ω. Find the ratio of its
speed as a generator to its speed as a motor, the line current in each case
being 75A. [Ans: 1.119]
3. A long shunt
compound generator delivers a load of 25 kW at 500 V, and has armature series
field and shunt field resistance of 0.05 Ω, 0.03 Ω and 250 Ω respectively.
Calculate the generated emf and armature current. [Ans: Eg=504.16 V, Ia=52 A]
4. The armature of a 4
pole, 250 V dc shunt motor is lap connected having 120 slots, each slot
containing of conductors. The flux per pole is 0.02 Wb and the current taken by
the motor is 25 A. Calculate the speed and the torque developed by the
armature. The field and armature resistance are 12.5 Ω and 0.1 Ω respectively. [Ans: Ia=23 V, Eb=247.7
V, N=774 rpm, Td= 70.28 N‒m]
5. A 6 pole dc motor
has 936 wave connected armature conductors. The useful flux per pole is 0.02 Wb
and the armature circuit resistance is 0.05 Ohm. Calculate (i) the speed and
(ii) the torque developed when its armature takes 35 A at 400 V. [Ans: N=408.65 rpm, Td=312.83 N‒m]
Basic Electronics and Electrical Engineering: Chapter 2: DC Machines : Tag: Basic Engineering : DC Generators and Motors - DC Machines: Exercise Problems
Basic Electronics and Electrical Engineering: Chapter 2: DC Machines
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