Electrical Machines are the devices which convert mechanical energy into electrical energy and vice versa. It is also used to transform one form of electrical energy into another. Electrical Machine’s work on the principle of electromagnetic forces, which lead to either mechanical or electrical operations. These technologies find diverse applications in the field of power generation, green energy and electrical transmissions.
Question 1: An _______________ energy conversion device is one which converts electrical to mechanical and mechanical to electrical form of energy.
a) electro-mechanical b) mechanical-electro
c) electrical d) mechanical
Explanation: The principle behind the conversion of mechanical to electrical and electrical
Question 2: Short pitched coil ___________ the generated EMF in the system.
a) increases b) decreases
c) either (a) or (b) d) none of these
Explanation: The effect of a short pitched coil
Question 3: Which of the following losses is evaluated using retardation test on DC shunt motor?
a) Iron losses b) Copper losses
c) Friction losses d) Stray losses
Answer: Stray losses
Explanation: Retardation test is used to find stray
Question 4: In the hopkinson’s test, Machine A has field current of 1.6A and B has field current of 1.4A. Which of the above machines acts as a motor?
a) A b) B
c) Both (a) and (b) d) none of these
Question 5: Which of the following is responsible for the change in terminal voltage, when the load on a generator is varied?
a) Armature reactance b) Leakage reactance
c) Armature resistance d) All of the above
Answer: Armature resistance
Explanation: Armature resistance generally causes reduction in air gap flux and, which further reduces
Question 6: In terms of operation, which of the following is similar to an induction motor?
a) Stepper motor b) Synchronous motor
c) Universal motor d) Transformer
Explanation: Induction motor has a similar operation as the transformer. It works on
Question 7: An induction motor with 1500 rpm speed will have
a) 2 Poles b) 3 Poles
c) 4 Poles d) 6 Poles
Answer: 2 Poles
Explanation: n = Synchronous speed (rpm) , f = supply frequency (induction motor), p = pair of poles per phase
Question 8: What is the effect on current, if the resistance of the field winding of the D.C. generator is increased?
a) Decreases b) Increases
b) Constant d) None of these
Explanation: If the resistance of the field winding is increased, current in the field decreases.
Question 9: ____________ can be used for braking purposes in electric trains.
a) D.C Motor b) Induction Motor
c) Induction generator d) All of these
Answer: Induction generator
Explanation: Induction generator runs at a very high speed, which is greater than the synchronous speed.
Question 10: Which of the following is used to maintain constant voltage at the end of the feeder?
a) Shunt Motor b) Differential compound DC
c) Induction Motor d) DC series generator
Answer: DC series generator
Explanation: In a DC series generator, end voltage increases as the load increases from no load to full load.