178 + Interview Questions in Design Of Synchronous Machines in Design Of Electrical Machines Page 4 InterviewSolution

151.	What should be done to the conductors in the overhang of the stator?(a) bracing(b) shaving(c) punching(d) compressingI got this question in quiz.My enquiry is from Construction of Hydro-Generators in division Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct choice is (a) bracing The explanation is: The CONDUCTORS in the overhang of the STATOR must be BRACED. Bracing is the process of RAISING the mechanical strength of the conductors.

Discussion

152.	What happens to the electromagnetic forces during the sudden short circuits at the line terminals?(a) the electromagnetic forces get increased by 250 times the force under normal full load condition(b) the electromagnetic forces get decreased by 250 times the force under normal full load condition(c) the electromagnetic forces get increased by 200 times the force under normal full load condition(d) the electromagnetic forces get decreased by 200 times the force under normal full load conditionThis question was posed to me in an online interview.I'm obligated to ask this question of Construction of Hydro-Generators topic in section Design of Synchronous Machines of Design of Electrical Machines
Answer» Right OPTION is (a) the ELECTROMAGNETIC forces get INCREASED by 250 times the force under NORMAL full load condition Explanation: The electromagnetic forces are directly proportional to the square of the CURRENT. It increases by 250 times the force under normal full load conditions.

Discussion

153.	What is the main advantage of a winding with multi-turns coils?(a) reduce the choosing of the value of stator slots(b) allows greater flexibility in selecting the value of stator slots(c) increases the flexibility in selecting the number of stator slots(d) has no effect on the number of stator slotsI had been asked this question in semester exam.This interesting question is from Construction of Hydro-Generators in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct OPTION is (b) allows greater flexibility in selecting the VALUE of stator slots To elaborate: The MAIN advantage of a WINDING with multi-turns COILS is that it allows a greater flexibility in selecting the value of stator slots. It in turn helps in choosing the required number of turns per phase.

Discussion

154.	What happens to the current in the windings during the sudden short circuits at the line terminals?(a) the current reduces to 15 times the full load current(b) the current increases to 15 times the full load current(c) the current reduces to 10 times the full load current(d) the current increases to 10 times the full load currentI have been asked this question in final exam.Asked question is from Construction of Hydro-Generators in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» Right answer is (b) the current increases to 15 TIMES the full load current For explanation I would say: The current in the windings during short circuit at the LINE terminals increases to about 15 times the full load current. It can ALSO increase to higher level depending on the DIRECT axis sub-transient reactance.

Discussion

155.	The capacity of the pull out machines used for making the coils limits the pole pitch to less than 0.8 m.(a) true(b) falseThis question was addressed to me during an online interview.My enquiry is from Construction of Hydro-Generators in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» CORRECT option is (a) true Easy explanation: The capacity of the pull out machines used for MAKING the COILS limits the POLE pitch to less than 0.8 m. The capacity of the pull out machines used for making coils limits the length of SLOT portion to about 3 m.

Discussion

156.	What among the following is the advantages of the star connection?(a) eliminates single frequency harmonics(b) eliminates double frequency harmonics(c) eliminates triple frequency harmonics(d) eliminates sinusoidal harmonicsI had been asked this question during a job interview.My enquiry is from Construction of Hydro-Generators topic in division Design of Synchronous Machines of Design of Electrical Machines
Answer» Right choice is (c) eliminates TRIPLE frequency harmonics The best I can explain: The hydro-generators stator WINDINGS are connected in the STAR connected with the neutral earthed. It eliminates the triple frequency harmonics from the line voltage.

Discussion

157.	How are the stator windings of all synchronous generator connected?(a) star-delta connection(b) star connection(c) star connection with neutral earthed(d) delta connectedThis question was posed to me during an internship interview.I'd like to ask this question from Construction of Hydro-Generators topic in section Design of Synchronous Machines of Design of Electrical Machines
Answer» Correct answer is (c) star connection with neutral earthed The best EXPLANATION: The STATOR WINDINGS of all the synchronous generator are connected in the star connection with neutral earthing. The main advantage that the winding has to be insulated to EARTH for the phase voltage and not the LINE voltage.

Discussion

158.	What is the thickness of the most commonly used grade for stator laminations?(a) 0.5 mm(b) 1 mm(c) 1.5 mm(d) 2 mmI had been asked this question during an interview.My query is from Construction of Hydro-Generators topic in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» CORRECT choice is (a) 0.5 mm The explanation is: The most commonly used grade for the STATOR laminations is grade 230. The THICKNESS of this most commonly used grade for the stator laminations is 0.5 mm.

Discussion

159.	What is the range of the outside diameter of the stator frame of the large hydro-generator?(a) 3-18 m(b) 2-18 m(c) 3.5-18 m(d) 4-18 mI had been asked this question by my college professor while I was bunking the class.This key question is from Construction of Hydro-Generators in division Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct answer is (C) 3.5-18 m Explanation: The MINIMUM value for the outside DIAMETER of the stator FRAME of the large hydro-generators is 3.5 m. The maximum value for the outside diameter of the stator frame of the large hydro-generators is 18 m.

Discussion

160.	The modern synchronous machines make use of non-directional cold rolled steel.(a) true(b) falseI had been asked this question in my homework.My question is based upon Construction of Hydro-Generators in section Design of Synchronous Machines of Design of Electrical Machines
Answer» RIGHT answer is (a) true Explanation: The MODERN synchronous machines make use of the non-directional COLD rolled steel which has electrical characteristics SIMILAR to that of the hot rolled steel. But the non-directional cold rolled steel has much improved mechanical characteristics.

Discussion

161.	Why is the stator core built up of laminations?(a) to reduce core loss(b) to reduce copper loss(c) to reduce iron loss(d) to reduce eddy current lossI had been asked this question during an interview for a job.My doubt is from Construction of Hydro-Generators in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct answer is (d) to reduce eddy current LOSS Easiest EXPLANATION: The stator CORE is built up of laminations in ORDER to reduce the eddy current loss. The loss in the laminated core is usually the single largest loss and hence the choice of type and grade of steel is of utmost importance.

Discussion

162.	What factors does the speed of the machines depend upon?(a) head(b) blades(c) type of turbine used(d) head and type of turbine usedThis question was posed to me by my college professor while I was bunking the class.This intriguing question comes from Construction of Hydro-Generators in division Design of Synchronous Machines of Design of Electrical Machines
Answer» Correct option is (d) head and TYPE of TURBINE used The explanation is: The hydro-generators are generally LOW speed machines. The speed depends UPON the head and the type of TURBINES used.

Discussion

163.	Which factor does the constructional feature of the hydro-generators depend on?(a) speed(b) voltage(c) power(d) currentThis question was posed to me during an online exam.This intriguing question comes from Construction of Hydro-Generators in division Design of Synchronous Machines of Design of Electrical Machines
Answer» The CORRECT option is (a) speed Explanation: The CONSTRUCTIONAL feature of hydro-generators are BASICALLY dependent upon the mechanical considerations. The main mechanical consideration is speed of the MACHINE.

Discussion

164.	How many factors are involved in the construction of hydro-generators?(a) 11(b) 10(c) 9(d) 8I have been asked this question in homework.Question is taken from Construction of Hydro-Generators topic in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» The CORRECT OPTION is (b) 10 Explanation: The hydro-generators are the SYNCHRONOUS generators that are driven by the water turbines. They are chosen based on 10 DIFFERENT categories.

Discussion

165.	What is the speed of the engine driven generators?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmThis question was addressed to me during an online interview.My doubt is from Types of Synchronous Machines in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct choice is (d) 3000 RPM To explain I WOULD say: The MAIN application of the synchronous compensators is to control the REACTIVE powers. They are designed to speeds upto 3000 rpm.

Discussion

166.	What is the rating of the synchronous generators?(a) 750 MVAr(b) 1000 MVAr(c) 100 MVAr(d) 700 MVArI had been asked this question during an online interview.This interesting question is from Types of Synchronous Machines topic in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» Correct CHOICE is (C) 100 MVAr To explain I would say: The main APPLICATION of the synchronous compensators is to control the REACTIVE POWERS. They are designed for ratings upto 100 MVAr.

Discussion

167.	Which among the following are the applications of synchronous motors?(a) compressors(b) blowers(c) fans(d) compressors, fans, blowersI have been asked this question in semester exam.I'd like to ask this question from Types of Synchronous Machines topic in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» Right choice is (d) compressors, FANS, blowers To elaborate: They are mainly USED in the high POWER and low SPEED applications. They include compressors, fans, blowers and low head pumps.

Discussion

168.	What is the application of synchronous compensators?(a) control of real power(b) control of active power(c) control of reactive power(d) control of apparent powerI have been asked this question in class test.Origin of the question is Types of Synchronous Machines topic in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» Correct option is (c) CONTROL of reactive power The explanation: The MAIN APPLICATION of the synchronous COMPENSATORS is to control the reactive powers. They are used in the power supply NETWORKS.

Discussion

169.	The synchronous motors are cheaper than the induction motors.(a) true(b) falseThis question was posed to me in class test.This intriguing question originated from Types of Synchronous Machines topic in division Design of Synchronous Machines of Design of Electrical Machines
Answer» CORRECT OPTION is (a) true The best I can explain: The synchronous motors are CHEAPER than the induction motors. They have high power lower SPEED APPLICATIONS and are cheaper when compared to the induction motors.

Discussion

170.	What is the rating of the engine driven generators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThe question was posed to me during an internship interview.I'd like to ask this question from Types of Synchronous Machines in section Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct choice is (c) 20 MW Explanation: The engine driven GENERATORS are driven by the different forms of internal combustion engine. These generators have HIGHER speeds for higher POWER ratings. These generators have ratings upto 20 MW.

Discussion

171.	How is the engine driven generators driven by?(a) water turbines(b) steam turbines(c) internal combustion engine(d) compensatorsI have been asked this question by my college director while I was bunking the class.This intriguing question comes from Types of Synchronous Machines in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» CORRECT choice is (c) internal combustion engine Easiest explanation: The engine DRIVEN generators are driven by the DIFFERENT forms of internal combustion engine. These generators have higher speeds for higher power ratings.

Discussion

172.	What is the rating of the turbo-alternators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThis question was posed to me in quiz.This key question is from Types of Synchronous Machines in section Design of Synchronous Machines of Design of Electrical Machines
Answer» Right answer is (b) 1000 MW The EXPLANATION is: The turbo alternators are one CATEGORY AMONG the synchronous MACHINES. They are driven by the steam turbines. The SPEED of the turbo-alternators is 1000 MW.

Discussion

173.	What is the speed of the turbo-alternators?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmThis question was addressed to me in exam.The above asked question is from Types of Synchronous Machines in division Design of Synchronous Machines of Design of Electrical Machines
Answer» RIGHT ANSWER is (d) 3000 rpm For explanation: The turbo alternators are ONE category among the SYNCHRONOUS machines. They are driven by STEAM turbines. The rating of the turbo-alternators is 3000 rpm.

Discussion

174.	How is the turbo-alternators driven by?(a) water turbines(b) steam turbines(c) engine driven generators(d) compensatorsI have been asked this question in a national level competition.This question is from Types of Synchronous Machines in chapter Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct option is (B) steam turbines Easiest EXPLANATION: The turbo alternators are one CATEGORY AMONG the synchronous machines. They are driven by the steam turbines.

Discussion

175.	What is the speed by which the hydro-generators are driven?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmI have been asked this question in examination.Enquiry is from Types of Synchronous Machines topic in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct choice is (a) 100-1000 rpm The explanation is: The SYNCHRONOUS generators which are driven by the WATER TURBINES are called as hydro-generators. The hydro-generators are driven at a speed of 100-1000 rpm.

Discussion

176.	How is the hydro-generator driven by?(a) water turbine(b) steam turbine(c) internal combustion engines(d) control of reactive power networksThis question was addressed to me in exam.The origin of the question is Types of Synchronous Machines in section Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct choice is (a) WATER turbine Best explanation: The synchronous generators which are driven by the water turbines are CALLED as hydro-generators. The hydro-generators are ALSO KNOWN as water WHEEL generators.

Discussion

177.	What is the rating of the hydro-generators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThis question was addressed to me in an interview for job.My question is based upon Types of Synchronous Machines topic in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» Right answer is (a) 750 MW The EXPLANATION is: The SYNCHRONOUS generators which are driven by the WATER turbines are CALLED as hydro-generators. The RATING of the synchronous generators is 750 MW.

Discussion

178.	How many categories can the synchronous motors be divided into?(a) 4(b) 3(c) 5(d) 2This question was addressed to me by my college professor while I was bunking the class.Asked question is from Types of Synchronous Machines topic in portion Design of Synchronous Machines of Design of Electrical Machines
Answer» The correct OPTION is (c) 5 To EXPLAIN I would say: The synchronous motors can be divided into 5 types of categories. They are hydro-generators, turbo-alternators, engine driven generators, motors, COMPENSATORS.

Discussion

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What should be done to the conductors in the overhang of the stator?(a) bracing(b) shaving(c) punching(d) compressingI got this question in quiz.My enquiry is from Construction of Hydro-Generators in division Design of Synchronous Machines of Design of Electrical Machines

What is the thickness of the most commonly used grade for stator laminations?(a) 0.5 mm(b) 1 mm(c) 1.5 mm(d) 2 mmI had been asked this question during an interview.My query is from Construction of Hydro-Generators topic in portion Design of Synchronous Machines of Design of Electrical Machines

The modern synchronous machines make use of non-directional cold rolled steel.(a) true(b) falseI had been asked this question in my homework.My question is based upon Construction of Hydro-Generators in section Design of Synchronous Machines of Design of Electrical Machines

How many factors are involved in the construction of hydro-generators?(a) 11(b) 10(c) 9(d) 8I have been asked this question in homework.Question is taken from Construction of Hydro-Generators topic in portion Design of Synchronous Machines of Design of Electrical Machines

What is the speed of the engine driven generators?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmThis question was addressed to me during an online interview.My doubt is from Types of Synchronous Machines in chapter Design of Synchronous Machines of Design of Electrical Machines

The synchronous motors are cheaper than the induction motors.(a) true(b) falseThis question was posed to me in class test.This intriguing question originated from Types of Synchronous Machines topic in division Design of Synchronous Machines of Design of Electrical Machines

What is the rating of the engine driven generators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThe question was posed to me during an internship interview.I'd like to ask this question from Types of Synchronous Machines in section Design of Synchronous Machines of Design of Electrical Machines

What is the rating of the turbo-alternators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThis question was posed to me in quiz.This key question is from Types of Synchronous Machines in section Design of Synchronous Machines of Design of Electrical Machines

What is the speed of the turbo-alternators?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmThis question was addressed to me in exam.The above asked question is from Types of Synchronous Machines in division Design of Synchronous Machines of Design of Electrical Machines

What is the speed by which the hydro-generators are driven?(a) 100-1000 rpm(b) 5000 rpm(c) 1500 rpm(d) 3000 rpmI have been asked this question in examination.Enquiry is from Types of Synchronous Machines topic in portion Design of Synchronous Machines of Design of Electrical Machines

What is the rating of the hydro-generators?(a) 750 MW(b) 1000 MW(c) 20 MW(d) 700 MWThis question was addressed to me in an interview for job.My question is based upon Types of Synchronous Machines topic in portion Design of Synchronous Machines of Design of Electrical Machines