Electrical Machines: DC Motor Overview

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What is the primary function of the stator in a DC motor?

Generate a magnetic field (correct)

Convert electrical energy into mechanical energy

Control the flow of Direct Current (DC)

Serve as the device's solid outer frame

Which component of a DC motor acts as a frame providing structural strength?

Carbon brushes

Field coil

Yoke (correct)

Commutator

What is the function of a commutator in a DC motor?

Switch the direction of current flow in the armature coil (correct)

Provide structural strength

Generate a magnetic field

Rotate the armature coil

Which component of a large DC motor replaces permanent magnets?

Field coil Signup and view all the answers

What interacts to apply torque on the armature of a DC motor?

Armature and stationary magnets Signup and view all the answers

What is the purpose of the pole shoe in a DC motor?

To maximize the magnetic flux to the armature Signup and view all the answers

How is the field winding of a DC motor powered?

By direct current Signup and view all the answers

In a DC motor, what is the function of the commutator?

To convert alternating torque to unidirectional torque Signup and view all the answers

What is the main advantage of a DC series motor for high starting loads?

It provides high starting torque Signup and view all the answers

How is the speed of a DC series motor affected by the load?

It increases as the load increases Signup and view all the answers

What is the additional primary current used for in a transformer?

To restore the original value of the flux in the core Signup and view all the answers

Why is the primary current I'1 called the primary counter-balancing current?

It is in phase opposition with the secondary current Signup and view all the answers

What does the induced magnetomotive force N1I'1 set up in the transformer?

Flux f'1 in the core Signup and view all the answers

What is the implication of I1' = (N2/N1)I2 = K I2 in transformer operation?

It defines the ratio of primary to secondary currents Signup and view all the answers

What determines the power factor of the secondary side of a transformer?

Type of load connected Signup and view all the answers

What is the speed equation for a DC series motor?

N = Eb/f Signup and view all the answers

What is the purpose of Buchholz relay in a single-phase transformer?

To guard against internal and early faults Signup and view all the answers

Why does the back EMF in a DC series motor decrease with an increase in armature current?

Due to the ohmic drop in armature and series field resistances Signup and view all the answers

What color does fresh silica gel crystals in the breather of a single-phase transformer have?

Blue Signup and view all the answers

Which characteristic of a DC series motor is also called mechanical characteristic?

Speed vs. Torque (N-Ta) Signup and view all the answers

What is the core of a single-phase transformer mainly made of?

Silicon steel Signup and view all the answers

When a transformer is operating on no load, what is the magnitude of the no-load current compared to the rated current?

5 to 15% of the rated current Signup and view all the answers

What is the main function of an explosion vent in a transformer?

To release excessive hot oil Signup and view all the answers

Why are laminations coated with insulating materials in the construction of a transformer core?

To prevent short circuit situations Signup and view all the answers

What is the angular relationship between the reactive component of the no-load current and the applied voltage in a transformer?

90 degrees Signup and view all the answers

What is the main difference between a DC Shunt Motor and a DC Compound Motor?

The DC Shunt Motor has a constant speed, while the DC Compound Motor has a speed that changes with load. Signup and view all the answers

How does the starting torque of a DC Shunt Motor compare to the starting torque of a DC Compound Motor?

The starting torque of a DC Shunt Motor is less than that of a DC Compound Motor. Signup and view all the answers

Why do DC Shunt Motors have a straight line torque and armature current characteristic?

Because the armature current and flux in a DC Shunt Motor are directly proportional. Signup and view all the answers

How does the speed of a DC Shunt Motor vary with an increase in load?

The speed decreases slightly as the load increases. Signup and view all the answers

Why does the shaft torque of a DC Series Motor lie slightly lower than the armature torque?

Because of stray losses in the motor. Signup and view all the answers

What is the term for the power dissipated in the form of heat due to the circulation of eddy currents?

Eddy current loss Signup and view all the answers

Which material is recommended for minimizing hysteresis loss in transformer cores?

Silicon steel Signup and view all the answers

What is the reason behind using thin laminations in transformer cores?

To decrease eddy current loss Signup and view all the answers

Which loss in a transformer remains constant regardless of the load?

Constant losses Signup and view all the answers

What factors contribute to copper losses in transformers?

Primary and secondary currents Signup and view all the answers

How can eddy current loss in transformers be reduced?

Increasing the thickness of the laminations Signup and view all the answers

Which equation is used to calculate hysteresis loss in transformers?

Ph = Kh V f Bm^2.6 Signup and view all the answers

What is the main reason for the occurrence of eddy current loss in transformers?

Alternating flux in the core Signup and view all the answers

Why are copper losses called variable losses in transformers?

Influence of load variations on winding currents Signup and view all the answers

What effect does the core material have on constant losses in transformers?

Has no impact on constant losses Signup and view all the answers