InterviewSolution

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1.	BLDC can be used instead ____________(a) Synchronous motor(b) Normal brushed DC motor(c) Induction motor(d) Air motorThis question was posed to me in a national level competition.I want to ask this question from BLDC Motors in section Synchronous Machines of DC Machines
Answer» The correct ANSWER is (b) Normal brushed DC motor Explanation: BRUSHLESS motors fulfil almost all FUNCTIONS originally performed by brushed DC motors, but cost and control complexity prevent brushless motors from replacing brushed motors completely in the lowest-cost areas. Brushless motors are now dominating many applications, particularly devices such as computer HARD drives and CD/DVD PLAYERS.

2.	Typical brushless motor doesn’t have ______________(a) Commutator(b) Permanent magnet(c) Electronic controller(d) Fixed armatureI had been asked this question during an online interview.My question is from BLDC Motors in division Synchronous Machines of DC Machines
Answer» The correct choice is (a) Commutator The explanation: A typical brushless motor has permanent magnets which rotate around a FIXED armature. An electronic CONTROLLER replaces the brush-commutator assembly of the brushed conventional DC motor, which continually switches the phase to the windings to KEEP the motor TURNING.

3.	In medical fields which DC motor is widely used?(a) PMDC(b) BLDC(c) Brushed DC motor(d) Cannot be determinedThe question was posed to me in quiz.Origin of the question is BLDC Motors in chapter Synchronous Machines of DC Machines
Answer» CORRECT choice is (b) BLDC To elaborate: BLDC MOTORS are widely used in VARIOUS applications of medical industry. Sensor less BLDC MOTOR and with sensor BLDC motors are used because of easy operation and high reliability compare to conventional motors.

4.	Construction of BLDC is exactly similar to the ______________(a) Conventional DC motor(b) Induction motor(c) Permanent magnet synchronous motor(d) Totally different constructionThis question was posed to me in quiz.My question is taken from BLDC Motors in division Synchronous Machines of DC Machines
Answer» Correct OPTION is (c) Permanent magnet synchronous motor For explanation I would say: Construction of BLDC motor is exactly SIMILAR to the PMSM i.e. permanent magnet synchronous motor. BLDC is CONSIDERED as machine working LIKE DC with construction similar to the AC synchronous machine.

5.	In BLDC motor driver module, we do not require ______________(a) SCRs(b) Power transistors(c) FETs(d) TransistorsI have been asked this question during an online interview.My enquiry is from BLDC Motors in portion Synchronous Machines of DC Machines
Answer» Right option is (d) Transistors Explanation: The STATOR is connected to a variable voltage CURRENT source through an inductor and an inverter COMPRISING six SCRS (S1 to S6). In place of SCRs, power transistor or FETs could be used according to power rating of the motor.

6.	Which of the following is not an advantage of BLDC motor over conventional DC motor.(a) Less maintenance(b) Long life(c) No risk of explosion or possibility of RF radiation(d) Low costI got this question in examination.The origin of the question is BLDC Motors in portion Synchronous Machines of DC Machines
Answer» Correct choice is (d) Low cost Explanation: The brushless DC motor being more expensive COMPARE to DC motor of same kW RATINGS, serves many other ADVANTAGES like long life, less maintenance, rapid response, linear characteristic, no SPARKING and many more.

7.	By electronic circuitry BLDC can be controlled for both constant and variable torque operation.(a) True(b) FalseThe question was asked in unit test.My question comes from BLDC Motors in division Synchronous Machines of DC Machines
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8.	In BLDC motor field winding is kept on _______________(a) Stator(b) Rotor(c) Can be placed anywhere(d) AbsentThis question was addressed to me by my college director while I was bunking the class.Question is taken from BLDC Motors in chapter Synchronous Machines of DC Machines
Answer» The correct choice is (b) Rotor Explanation: Unlike conventional DC MOTOR, BLDC motor has its field WINDING rotating. Unlike PMDC motor field winding is present. THUS, it is placed on rotor. In BLDC motor we have fixed commutators, with brush gear rotating with speed of rotor field.