InterviewSolution

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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.	The armature of DC motor is laminated to ____________(a) To reduce mass(b) To reduce hysteresis loss(c) To reduce eddy current loss(d) To reduce inductanceI have been asked this question by my college director while I was bunking the class.I want to ask this question from Construction in portion DC Machines of DC Machines
Answer» Correct answer is (c) To reduce EDDY current loss Easiest explanation: The armature is built up in a cylindrical or drum shape high grade silicon steel in form of lamination. By using laminations, the CIRCULAR path of eddy currents is terminated. HENCE heating and ultimately damage to the armature can be REDUCED by lamination.

2.	If a DC motor is connected to AC supply what will happen then?(a) Not run(b) Burn(c) Run at normal speed(d) Run at extremely low speedThe question was asked in semester exam.Query is from Construction in division DC Machines of DC Machines
Answer» Right answer is (b) Burn Easiest explanation: If a DC motor is connected to AC supply, an alternating current pass through the BRUSHES and commutator to the armature winding, while it passes through the commutator it is converted into DC so that the group of conductors under SUCCESSIVE field poles carry current in same direction. So, the FLUX per pole will remain constant and not VARY. There will be production of HEAT due to flow of eddy current in field winding and the motor will be burned.

3.	In a DC machine, rectification process is carried out in order to get unidirectional output (DC). This rectification process is carried out by ______________(a) Half wave rectifier(b) Full wave rectifier(c) Mechanical rectification(d) Centre tapped rectifierI had been asked this question in a job interview.My question is taken from Construction in portion DC Machines of DC Machines
Answer» RIGHT OPTION is (c) Mechanical rectification To elaborate: In a DC machine electronic rectification is not used. Instead they USE mechanical rectification with the help of commutator-brush ASSEMBLY.

4.	In normal dc machines operating at full-load conditions, the most powerful electromagnet is _________(a) Field winding(b) Interpole Winding(c) Interpole and compensating winding together(d) Armature windingThe question was asked during an interview.My question comes from Construction topic in portion DC Machines of DC Machines
Answer» Right choice is (a) Field winding For EXPLANATION: Electromagnet is more powerful when its MMF is high. At full-load condition, field winding contains MAXIMUM ampere turns, HENCE it is most powerful electromagnet in a DC machine.

5.	The angle (electrical) made by brushes with axes of adjoining filed poles is ______________(a) 450(b) 1800(c) 900(d) 300I got this question during an online interview.The above asked question is from Construction topic in division DC Machines of DC Machines
Answer» The CORRECT ANSWER is (C) 900 Explanation: Brushes in a DC MACHINE are normally placed electrically in the interpolar regions and therefore MAKE an angle of 900 electrical with the axes of adjoining filed poles.

6.	Where is field winding mounted in a DC machine?(a) Stator(b) Rotor(c) Absent(d) Anywhere on stator or rotorThis question was addressed to me in an interview for job.This intriguing question comes from Construction in division DC Machines of DC Machines
Answer» RIGHT option is (a) Stator For explanation: The field winding (concentrated type) is mounted on salient-poles on the stator and the ARMATURE winding (distributed type) is WOUND in slots on a cylindrical ROTOR. In AC machines field winding is mounted on rotor.

7.	In a DC machine fractional pitch winding is used to _______________(a) To improve cooling(b) To reduce sparking(c) To reduce copper losses(d) To increase generated EMFThe question was posed to me by my college director while I was bunking the class.My query is from Construction in portion DC Machines of DC Machines
Answer» The correct choice is (B) To reduce sparking Best EXPLANATION: Due to poor performance of brush, poor UNDERCUTTING of commutator, incorrect spring pressure sparking at brush faces happen. To OVERCOME this sparking fractional pitch winding is used.

8.	What are the materials used for brushes in dc machines?(a) Iron(b) Carbon(c) Aluminum(d) SteelI had been asked this question by my school principal while I was bunking the class.This key question is from Construction in section DC Machines of DC Machines
Answer» RIGHT answer is (b) CARBON Explanation: On some EXTENT carbon brush can act as a self-lubricating brush. On moment, polishes the commutator segments. Damage to the commutators is less when COPPER BRUSHES are used on occurrence of sparkover.

9.	Which of the following part is used in construction of DC machine but not in AC machine?(a) Armature Winding(b) Field winding(c) Commutator(d) ShaftThis question was posed to me in quiz.Asked question is from Construction topic in section DC Machines of DC Machines
Answer» Correct OPTION is (C) Commutator The explanation is: Commutator is USED in mechanical rectification process, to convert induced AC to OUTPUT DC. In AC machine, we don’t need rectification process.

10.	Function of yoke is to provide the return path for magnetic flux.(a) True(b) falseI had been asked this question in an international level competition.My question comes from Construction in chapter DC Machines of DC Machines
Answer» The correct answer is (a) True To EXPLAIN: The function of yoke is that it PROTECTS the entire machine from dust and DIRT. It also provides MECHANICAL support for the magnetic poles. It acts as the RETURN path for the magnetic flux.