Electrical Fundamentals Module 3: DC Motors/Generators

<p>In a shunt-wound motor, the field is connected in parallel with the armature. (A)</p> Signup and view all the answers

<p>They are almost always used for practical applications. (D)</p> Signup and view all the answers

<p>Series motors develop large torque from standstill unlike shunt-wound motors. (B)</p> Signup and view all the answers

<p>Always connect a load before starting the motor. (D)</p> Signup and view all the answers

<p>It allows for enhanced speed control under normal conditions. (A)</p> Signup and view all the answers

<p>Cumulative compound motor with aiding fields (C)</p> Signup and view all the answers

<p>Torque decreases, and speed also decreases (A)</p> Signup and view all the answers

<p>It opposes the shunt winding's magnetic field (C)</p> Signup and view all the answers

<p>Independent field circuit (B)</p> Signup and view all the answers

<p>Magnetism of the field winding is reversed (C)</p> Signup and view all the answers

<p>Cumulative compound motor (C)</p> Signup and view all the answers

<p>Reversal of motor direction (B)</p> Signup and view all the answers

<p>Using a rheostat in series with the armature (A)</p> Signup and view all the answers

<p>Improved speed regulation by the shunt field (B)</p> Signup and view all the answers

<p>Field rheostat (D)</p> Signup and view all the answers

<p>Split field motor (B)</p> Signup and view all the answers

<p>Reduces the torque and speed (C)</p> Signup and view all the answers

<p>Acts to oppose the supply voltage (D)</p> Signup and view all the answers

<p>Inability to maintain constant speed under all load conditions (B)</p> Signup and view all the answers

<p>Minimizing brush sparking (C)</p> Signup and view all the answers

<p>Armature rheostat (C)</p> Signup and view all the answers

<p>The magnetic field is perpendicular to the conductor. (A)</p> Signup and view all the answers

<p>Current direction in the armature (C)</p> Signup and view all the answers

<p>Magnitude of armature current (B)</p> Signup and view all the answers

<p>Both can vary their torque based on load conditions. (C)</p> Signup and view all the answers

<p>To provide an initial speed boost for the motor (C)</p> Signup and view all the answers

<p>It acts to oppose the supply voltage and limit current. (D)</p> Signup and view all the answers

<p>Reversing the armature current reverses the direction of rotation. (A)</p> Signup and view all the answers

<p>They optimize torque and speed under varying load conditions. (A)</p> Signup and view all the answers

<p>It shifts in the direction of rotation. (B)</p> Signup and view all the answers

<p>To cancel the effects of the armature magnetic field. (B)</p> Signup and view all the answers

<p>Shift brushes to the new neutral plane. (C)</p> Signup and view all the answers

<p>They shift the neutral plane in the opposite direction of armature magnetic field shifts. (C)</p> Signup and view all the answers

<p>It opposes the rotation of the armature requiring more mechanical force. (D)</p> Signup and view all the answers

<p>Because shifting brush position is usually not practiced, except in small generators. (A)</p> Signup and view all the answers

<p>It remains stationary regardless of changes in load. (C)</p> Signup and view all the answers

<p>Shorting coils with voltage in them. (B)</p> Signup and view all the answers

<p>Interpoles have fewer turns of larger wire compared to the main poles. (C)</p> Signup and view all the answers

<p>When only field windings are excited. (C)</p> Signup and view all the answers

<p>Because of the interaction between conductor field and main field. (C)</p> Signup and view all the answers

<p>The load placed on the generator. (A)</p> Signup and view all the answers

<p>Distortion of opposing fields in the generator. (D)</p> Signup and view all the answers

<p>It increases the motor reaction force, requiring more applied mechanical force. (B)</p> Signup and view all the answers

<p>To maintain a stationary neutral plane regardless of load. (D)</p> Signup and view all the answers

<p>The neutral plane remains unaffected. (A)</p> Signup and view all the answers

<p>It may lead to excessive speed, causing damage. (B)</p> Signup and view all the answers

<p>The input power. (A)</p> Signup and view all the answers

<p>High-speed electric trains. (D)</p> Signup and view all the answers

<p>Torque increases due to series field contribution. (C)</p> Signup and view all the answers

<p>Field circuit connection. (C)</p> Signup and view all the answers

<p>Rheostat. (B)</p> Signup and view all the answers

<p>To allow loading during operation. (B)</p> Signup and view all the answers

<p>Rheostat. (C)</p> Signup and view all the answers

<p>An independent current source (C)</p> Signup and view all the answers

<p>Field pole pieces must retain some residual magnetism (A)</p> Signup and view all the answers

<p>Conductor carrying current and within a magnetic field (B)</p> Signup and view all the answers

<p>It attempts to move perpendicular to the magnetic field (B)</p> Signup and view all the answers

<p>Self-excited generator (D)</p> Signup and view all the answers

<p>It allows for easy variation in strength (C)</p> Signup and view all the answers

<p>The conductor must be carrying current (B)</p> Signup and view all the answers

<p>It is crucial for the initial start-up (C)</p> Signup and view all the answers

<p>The field flux remains constant due to parallel connection. (B)</p> Signup and view all the answers

<p>Rheostat connected in series with the shunt field. (C)</p> Signup and view all the answers

<p>It causes the motor to speed up due to increased flux. (D)</p> Signup and view all the answers

<p>Less current flows through the shunt field, weakening the magnetic field. (A)</p> Signup and view all the answers

<p>Armature current increases, causing the motor to speed up. (A)</p> Signup and view all the answers

<p>The motor will slow down temporarily before stabilizing due to changed current flow. (B)</p> Signup and view all the answers

<p>They lack sufficient starting torque. (A)</p> Signup and view all the answers

<p>Decreased field strength results in increased armature current for speed stability. (D)</p> Signup and view all the answers

DC motors are similar to DC generators but control input instead of output. They come in series wound, shunt wound, compound wound, and separately excited/permanent magnet varieties.

A DC motor where the field winding is connected in series with the armature. It creates high starting torque, but has variable speed.

A series motor needs a load connected before starting to prevent excessive speed, which can damage the motor.

Series motors are best used in applications requiring high starting torque like cranes or winches.

Another type of DC motor, this one has a shunt field winding, giving a more stable speed.

A type of DC motor with both series and shunt field windings, combining the advantages of both.

A DC motor where the field winding is powered independently from the armature. This provides good control over speed.

Speed control in motors such as series motors is often achieved with a variable resistor (rheostat) in parallel with the armature.

Reducing shunt motor speed involves decreasing armature current using a rheostat in series with the armature.

Higher armature current leads to more torque and faster motor speed.

A DC motor with two field windings: a shunt field (parallel) and a series field (in series with the armature).

In a compound motor, the shunt field is connected in parallel with both the series field and armature.

A compound motor where the series field aids the shunt field, creating a stronger combined magnetic field.

A compound motor where the series field opposes the shunt field, resulting in a lower starting torque.

Typically controlled similarly to shunt motors (field control).

Cumulative compound motors are suitable for applications requiring uniform speed and good starting torque, while differential compound motors are used for low-power applications.

A DC motor with a separate field circuit powered by a different source than the armature circuit.

Adjusting speed of a separately excited motor involves using rheostats (variable resistors) in circuits.

Separately excited motors excel at providing high torque at low speeds.

Changing the direction of a DC motor's rotation requires reversing current flow in the armature or field windings.

A motor using two field windings in opposite directions on the same pole to reverse rotation.

A method for reversing motor direction using a double pole, double throw (DPDT) switch to change the current flow in the armature or field.

A series motor with multiple field windings to change the direction of rotation.

Reversing wires connecting the power supply to the motor does not change the motor's rotational direction.

A rule to determine the direction of a magnetic field around a current-carrying conductor.

Perpendicular to the current-carrying conductor.

The fundamental principles behind the operation of DC motors and generators.

Parts of a DC generator and their functions (e.g., armature, field windings).

The electrical power produced by a DC generator.

The mechanical power delivered by a DC motor.

The turning force produced by a DC motor.

The rate at which a DC motor rotates.

The magnetic field produced by the armature current that interacts with the main field, distorting the magnetic field and affecting generator performance.

The distortion of the main magnetic field in a DC generator caused by the armature current.

The change in position of the neutral plane due to Armature Reaction, making it move with rotation.

Coils placed in slots in pole faces to counteract armature reaction; connected in series with the armature, creating a field that opposes the armature's magnetic field.

No change in neutral plane if only armature is working without any field current

Small auxiliary poles placed between main field poles in DC generators; used to reduce armature reaction, connected in series with the armature.

Moving the brushes to the new neutral plane to avoid sparking.

The magnetic force that opposes the rotation of the armature of a DC generator, created by armature current flowing.

Variations in the generator's load current cause the neutral plane to shift.

The plane in the middle of the poles where there is no voltage when the machine is operating.

Correct location of brushes in a DC machine to minimize voltage and current problems.

Shifting brushes to the new neutral plane does not completely resolve the problems related to armature reaction, especially with high load variations.

The ideal neutral plane for commutation is not the same as the actual neutral plane due to armature reaction.

Small poles added to a generator to reduce the effects of armature reaction, which are connected in series with the armature.

The neutral plane is not affected if only the field windings are excited, and the armature is not connected, or if field is not excited.

The current delivered to the generator external load.

The creation of a steady magnetic field in a generator or motor by applying a DC voltage to the field windings, causing current to flow.

A DC generator where the field windings are powered by a separate source, independent of the generator's output.

A DC generator where the field windings are supplied by the generator's own output, requiring an initial residual magnetism.

A force is induced on a current-carrying conductor within a magnetic field, perpendicular to the field.

A conductor must carry current and be inside a magnetic field.

The strength of a magnetic field, that can be varied by the amount of current in the field windings.

A machine that converts electrical energy into mechanical energy.

A conductor that has electrical current flowing through it.

DC motors are similar to DC generators but control input instead of output, categorized as series, shunt, compound, and separately excited/permanent magnet.

DC motor with field winding connected in series with the armature, creating high starting torque but variable speed.

Series motors require a connected load to prevent excessive speed and damage.

Suitable for appliances, tools, cranes, and winches needing high starting torque.

Adjusting a series motor's speed involves a rheostat connected in parallel with the armature.

A series motor's speed increases without load to dangerously high levels.

The field winding is in series with the armature in series wound DC motors.

Speed control for a series motor below normal speed using a variable resistor connected in parallel with the armature.

Relatively constant speed regardless of load changes, remaining within 10-15% variation.

Field windings are connected in parallel (shunt) with the armature windings.

Good starting torque, but not suited for very heavy starting loads.

Controlling speed above normal speed of DC shunt motor by adjusting field current using rheostat in series with shunt field.

Decreasing field current reduces magnetic field strength, lowering armature counter-electromotive force (CEMF), which results in increase in armature current.

A Rheostat in series with a motor field adjusts the current flowing through the field winding.

Increased load on a shunt motor causes it to slow down, decreasing counter-electromotive force (CEMF).Armature current increases to restore original speed.

Suitable for applications needing uniform speed (regardless of load), e.g., blowers where mechanical load is after motor speed reaches desired level.