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Do AC induction motors have back EMF?

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Answer : In case of D.C. shunt motors the speed is dependent on back e.m.f. only because flux is practically constant in D:C. shunt motors.

Description : What is back emf? 

Answer : Back EMF: When a current carrying conductor is placed in a magnetic field it experiences a force; when it moves due to the force it (conductor) cuts the magnetic field due to which an emf is ... (hence the applied armature voltage) is opposed by the induced emf which is therefore called as Back emf.

Description : What is back EMF of synchronous motor?

Description : What is back EMF in inductor?

Description : What is the back EMF in Transformers?

Description : What is the back EMF of a dc motor?

Description : What is the back EMF of the motor?

Description : What is the back EMF?

Answer : When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The ... that energy conversion in a d.c. motor is only possible due to the production of back emf.

Description : The back emf of synchronous motor depends on?

Answer : The back emf of synchronous motor depends on load angle.

Description : Why are DC motors used in trains and not AC motors ?

Answer : The reason is torque. torque is inversely proportional to speed..i.e when th knowe train comes to rest position to motion.. initial speed is zero..so it requires high starting torque for ... current will flow through field and armature coils then maximum torque is available at the intial condition.

Description : Which of the following motors can run on both AC and DC? A) Universal motor B) Dual wattage motor C) Flexible motor D) All the above

Answer : Which of the following motors can run on both AC and DC? A) Universal motor B) Dual wattage motor C) Flexible motor D) All the above

Answer : The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 0.5.

Answer : The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.

Description : Slot harmonics are reduced in induction motors by using (A) fractional-pitch windings (B) fractional-slot windings (C) integral-slot windings (D) distributed windings

Answer : Slot harmonics are reduced in induction motors by using fractional-slot windings

Description : Generally, Crawling in squirrel cage induction motors is tendency to run stably at speeds as low as (A) One-third of their synchronous speed (B) One-fifth of their synchronous speed (C) One-seventh of their synchronous speed (D) One-ninth of their synchronous speed

Answer : Generally, Crawling in squirrel cage induction motors is tendency to run stably at speeds as low as One-seventh of their synchronous speed

Answer : Induction motor is a AC motor it is also known as asynchronous motor .

Answer : The capacitors used in single-phase capacitor motors have no polarity marking.

Answer : Most of the fractional horsepower motors have either plain or sleeve bearings.

Description : Self induced emf and Mutually induced emf

Answer : (i) Self-induced e.m.f.: The e.m.f. induced in a coil due to the change of its own flux linked with it, is called self-induced e.m.f.  (ii) Mutually induced e.m.f.: The e.m.f. induced in a coil due to the changing current in the neighbouring coil, is called mutually induced e.m.f. 

Description : What is Phase sequence? Draw waveforms of 3 phase emf.

Answer : Phase sequence: It is the order in which the three phases reach their peak or maximum values. It is shown in below fig. the phase sequence is A-B-C (or R-Y-B). In the following waveforms, it is ... 120º, B- phase voltage attains its positive maximum value. So the phase sequence is R-Y-B. 

Description : Compare statically induced emf with dynamically induced emf on any four points.

Answer : Statically induced emf Dynamically induced emf Emf is induced without any relative motion between conductor and magnetic field. Emf is induced due to relative motion between conductor ... induced in transformer windings e.g emf induced in Generator, Alternator armature windings

Description : Explain the term self induced EMF with a neat diagram.

Description : Define: 1) statically induced EMF 2) dynamically induced EMF Write the names of equipments in which these two types of EMF get induced

Answer : Concept of statically induced emf: The emf induced in coil or conductors without any relative motion between it and magnetic field is called statically induced emf. When conductor is stationary and flux ... it. This emf is dynamically induced emf. e.g. Emf induced in generators, alternator.

Description : List the two types of induced EMF.

Answer : There are two types of EMF one is statically induced EMF and second is dynamically induced EMF.

Description : Symptoms of Back Pain Causes And Tips

Answer : Symptoms of Back Pain Causes And Tips Back pain is the most common complaint heard among the adults these days. It has been estimated that people do suffer from back pain at least once in their ... night sleep that will recover from all the bodily disorders and you wake up fresh the next morning.

Description : Suggest electric motors for i) traction ii) crane iii) lathe machine iv) domestic fan.

Answer : i) Traction :- DC Series motor  ii) Crane :- DC Series motor  iii) Lathe machine :- 3 phase Induction motor or DC shunt motor  iv) Domestic fan :- 1 phase induction motor

Description : State which electric motors are generally used in electro agro systems with reason.

Answer : 1) 3 phase induction motor is used in electro agro system for water pumping from wells as 3 phase ac supply is easily available, cost of induction motor is less, maintenance free being rugged ... as 1 phase ac supply is easily available for domestic purpose, repair is simple and easily available.

Description : State factors for selection of motors as drive.

Answer : Following Factors governing / or are considered while selecting electric drive (Motor) for particular application: Factors to be considered for selection of Electrical Drives: 1) Nature of Supply:- ... level, load equalization 7) Cost: - Capital, Running and maintenance cost should be less.

Description : Compare variable reluctance and permanent magnet motors.

Answer : Variable reluctance Motor  Permanent magnet motors   The rotor is not magnetised The rotor is magnetised  High torque to inertia ratio  Low torque to inertia ratio  ... rotor has salient pole construction The rotor has mostly smooth cylindrical type of construction. 

Description : What are the factors to be considered while selection of motors for different drives?

Answer : Following Factors are considered while selecting electric drive (Motor) for particular application:  Factors to be considered for selection of Electrical Drives:  1) Nature of Supply:- Whether supply ... , load equalization 7) Cost: - Capital, Running and maintenance cost should be less.  

Description : 3 phase motor  42 hp  same ratting two motors  but pole change 2 and 4 pole   tell me difference amp of both motors

Description : Explain dynamic and static induced emf with neat diagram.

Answer : Dynamically Induced EMF:-  In this case, either coil moves or magnet moves, so that there is relative motion between coil & magnetic field. Thus magnetic field is cut by coil & emf is induced in it. The emf ... The expression for induced EMF is e= -L(di/dt) or = -N(dϕ/dt).

Description : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V

Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

Description : The fractional-pitch used for eliminating 7th harmonic from the emf wave of an alternator is (A) 2/3 (B) 5/6 (C) 7/8 (D) 6/7

Answer : The fractional-pitch used for eliminating 7th harmonic from the emf wave of an alternator is 6/7

Description : What is the EMF equation of the transformer?

Answer : E1 =2(3.142)fN1 (flux)1E2 =2(3.142)fN2(flux)2

Description : Why does induction motor have high starting current?

Answer : In induction motor , the flux produce is quadrature to the applied voltage. Since when we are going to start motor , there is no flux present inside . So in order to lets say compensate it ... times of current to further increase flux. So that is reason for high starting current in induction motor

Description : Do cell phones use AC or DC current?

Answer : DC of course.

Description : Why do we use AC current in our homes?

Answer : We used it for cooking rice,  For washing clothes and for lights in the house.

Description : A relay used for protection of motors against overload is :  (A) Impedance relay (B) Electromagnetic attraction type (C) Thermal relay (D) Buchholz's relay

Answer : A relay used for protection of motors against overload is : Thermal relay

Description : Damper winding is provided in 3 phase synchronous motors to :

Answer : Damper winding is provided in 3 phase synchronous motors to : provide starting torque and prevent hunting

Description : Stepper motors are used in  (1) printers (2) lifts (3) amplifiers (4) oscillators

Answer : Stepper motors are used in printers 

Description : Which of the following test is usually conducted to determine the efficiency of traction motors ? (A) Field’s test (B) Swinburne’s test (C) Hopkinson’s test (D) Retardation test.

Answer : Which of the following test is usually conducted to determine the efficiency of traction motors ? (A) Field’s test (B) Swinburne’s test (C) Hopkinson’s test (D) Retardation test.

Description : Which of the following motors is being extensively used in servo applications ? A. AC motor B. Field controlled dc motor C. Armature controlled dc motor D. None of these

Answer : Which of the following motors is being extensively used in servo applications ? A. AC motor B. Field controlled dc motor C. Armature controlled dc motor D. None of these

Answer : During rheostat braking of D.C. series motors motor is run as a generator.

Answer : D.C. shunt motors are used for driving machine tools.

Answer : The D.C. motors preferred for traction applications beacuse the speed is inversely proportional to the torque and the torque is proportional to square of armature current.

Description : In case of conductively compensated D.C. series motors, the compensating winding is provided?

Answer : In case of conductively compensated D.C. series motors, the compensating winding is provided in series with armature winding.

Answer : A direct online starter is used for starting motors up to 5 H.P.

Answer : When two D.C. series motors are connected in parallel, the resultant speed is normal speed.

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