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Starters are used with D.C. motors because to restrict armature current as there is no back e.m.f. while starting.

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Answer :

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

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Description :

State starters used for i) 3-Ph squirrel cage induction motor (3HP) ii) D.C. motor 

Answer :

Name the starters used for following motors : i) 3 H.P. 3-Ph squirrel cage I.M: i) DOL starter OR ii) Star-Delta Starter OR ii) Auto transformer starter OR iii) Soft start starter.  ii) D.C Shunt Motor : 1) Armature resistance starter (Three Point Starter) OR 2) Four Point Starter 

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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.

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

Answer :

Stepper motors are used in printers 

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What are the five types of single phase motors used in the industry?

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Answer :

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

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

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

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Answer :

In D.C. shunt motors as load is reduced the speed will remain almost constant.

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Answer :

Differentially compound D.C. motors can find applications requiring low starting torque.

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Description :

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

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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.

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Description :

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.

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Description :

What is the advantage of using soft starters?

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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

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Description :

Answer :

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

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Description :

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In D.C. machines fractional pitch winding is used to reduce the sparking.

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328 views 1 answer
Description :

Answer :

The type of D.C. motor used for shears and punches is cumulative compound D.C. motor.

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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

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Description :

In a dc machine, interpoles are used to  (1) neutralize the effect of armature reaction in the interpolar region (2) generate more induced emf in the armature (3) avoid interference of the armature flux with the main -field flux (4) reduce the demagnetizing effect of armature reaction

Answer :

In a dc machine, interpoles are used to neutralize the effect of armature reaction in the interpolar region

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92 views 1 answer
Description :

Explain selection of starters for Industrial Installation. 

Answer :

selection of starters for Industrial Installation: Every motor must be provided with a starter to start and stop the motor. It shall be within the sight of a person at the motor. It shall be so arranged as ... -Auto transformer starter  Slip ring I.M.------------------Rotor resistance starter

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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

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Description :

Answer :

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

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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.

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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

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Answer :

As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for sound equipment.

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Answer :

Synchronous motors are generally not self-starting because the direction of instantaneous torque reverses after half cycle.

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Answer :

The voltage used for suburban trains in D.C. system is usually 600 to 750 V.

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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

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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

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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.

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Answer :

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

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What is the difference between synchronous and asynchronous motors?

Answer :

The motor which rotates at constant speed is called synchronous motor. And that constant speed is called as synchronous speed.  And the motor which does not rotates at constant speed are called asynchronous motor. Asynchronous motor is also called as Induction motor.

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The efficiencies of transformers compared with that of electric motors of the same power are?

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Transformers have high efficiency than the same ratted motors

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How is a thyristor used to convert AC to DC?

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Which type of starter is used to start the DC motor?

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Why DC motor is used for traction?

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Answer :

In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to improve power factor.

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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.  

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Description :

Answer :

The standard full-load power factor ratings for synchronous motors are unity or 0.8 leading.

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Description :

Answer :

Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be cumulatively compounded.

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305 views 1 answer
Description :

Aluminium is not used as winding wire for the armature of a dc machine because  (1) aluminium has low resistivity (2) a large winding space is taken by aluminium conductors and creates jointing problems (3) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper

Answer :

Aluminium is not used as winding wire for the armature of a dc machine because  (2) a large winding space is taken by aluminium conductors and creates jointing problems (3) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper

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Description :

Answer :

Sparking, is discouraged in a D.C. motor because commutator gets damaged.

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118 views 1 answer
Description :

Answer :

For starting a D.C. motor a starter is required because it limits the starting current to a safe value.

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66 views 1 answer
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

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40 views 1 answer
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.

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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. 

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

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Answer :

The range of efficiency for shaded pole motors is 5% to 35%.

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In capacitor start single-phase motors current in the starting winding leads the voltage.

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Answer :

For power factor correction, synchronous motors operate at no-load and greatly over-excited fields.

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