Motors and Motor Control Circuits Quiz: Coursera Answers

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Questions and Answers

What is the purpose of the control circuit in a two-speed motor?

To plug and unplug the motor

To switch between electrically separate windings

To connect the windings in different configurations to change the speed (correct)

To reverse the motor

What does the overload protection in a motor circuit primarily protect against?

Overheating due to motor overload (correct)

Connection errors in the control circuit

Motor malfunction due to low voltage

Excessive loading of the motor

How does the control circuit prevent plugging of the motor?

By connecting both windings in series

By avoiding immediate reversal of the motor (correct)

By disconnecting one of the windings

By applying varying voltages to the windings

What effect does connecting the motor windings in different configurations have on the speed?

Changes the speed from one rpm to another Signup and view all the answers

Why are there two electrically separate windings in the two-speed motor?

As a backup in case one winding fails Signup and view all the answers

How does the overload protection safeguard the starter components?

By preventing high currents from damaging components Signup and view all the answers

Why is plugging not allowed in a two-speed motor?

It can lead to abrupt stops causing mechanical stress. Signup and view all the answers

What is the consequence of excessive overheating in a motor due to overload?

Damage to conductors in the control circuit Signup and view all the answers

How does connecting both windings in series affect motor performance?

Increases horsepower at low speeds Signup and view all the answers

What is the primary purpose of the overload protection in a motor circuit?

To prevent the motor from excessive overheating Signup and view all the answers

Why can the motor be reversed but not plugged in the anti-plugging circuit?

Plugging leads to excessive overheating Signup and view all the answers

How does connecting both windings in parallel affect a two-speed motor's performance?

Increases the motor's horsepower Signup and view all the answers

What is the consequence of excessive overheating in a motor due to overload?

Reduced starter component lifespan Signup and view all the answers

Why are two electrically separate windings housed in a two-speed motor?

To provide different speed options Signup and view all the answers

What effect does connecting the motor windings in series have on its performance?

Decreases motor horsepower Signup and view all the answers

How does the control circuit contribute to the protection of a two-speed motor?

By preventing overheating of conductors Signup and view all the answers

What happens when a motor is plugged according to the anti-plugging circuit?

Starter components heat up excessively Signup and view all the answers

How does connecting the windings in different configurations impact the two-speed motor?

Changes speed from one rpm to another Signup and view all the answers

What is NOT allowed in a two-speed motor?

Increasing horsepower Signup and view all the answers

Study Notes

Wire Control Circuits

Two-Wire Control Circuit: used for auto start operation of a motor after a power failure, depending on the position of the control contact (e.g., level switch or temperature switch contact).
Three-Wire Control Circuit: used for start/stop operation, where the NO contact of the start pushbutton and NC contact of the stop pushbutton are in series with the main contactor in the control circuit.

Jog Circuits

Jog/Inch Circuit: designed for a three-phase motor, where the motor runs when the jog pushbutton is pressed and stops when the pushbutton is released.
Jog Circuit using PB: the latching circuit to the starter coil (K) is opened by the NC contacts of the jog pushbutton, so the starter coil (K) remains energized as long as the jog button is fully pressed.
Jog Circuit using Selector Switch: the motor can be operated in run or jog mode, depending on the position of the selector switch.

Sequence Start and Stop Circuits

Sequence Start and Stop: used in large industrial plants to start and stop machines and drives in a predetermined sequence, using sequencers (mechanical or electromechanical).

Reversing Circuits

Reversing Circuit: an interchange of any two phases reverts the direction of a three-phase motor, running it in the reverse direction.

Jog Type For/Rev/Off Circuits

Jog Type For/Rev/Off Circuit using Selector Switch: interchanging any two leads to a three-phase induction motor causes it to run in the reverse direction, using a three-phase reversing starter with two contactors (K1 and K2) and a spring return-type selector switch.
Latch Type For/Rev/Stop Circuit using Pushbuttons: pressing the forward pushbutton energizes the contactor K1 coil, connecting the supply leads to the motor leads in the same phase sequence, causing the motor to rotate in a forward direction.

Plug Stop and Anti-Plug Circuits

Plug Stop and Anti-Plug Circuits: used to halt a motor or stop a running motor, using electric braking circuits that produce a retarding torque and dissipate the kinetic energy of the rotor and load as heat in the rotor bars.
Plugging: a motor is connected to run in a reverse direction while still running in a forward direction, resulting in motor stoppage, using a switch or contact that gives the status of the motor.
Anti-Plugging: protection is necessary when a motor with large inertia is connected suddenly in a reverse direction, while the motor is still running in a forward direction, to prevent the application of a counter torque until the motor speed is reduced to an acceptable value.

Two-Speed Motor Control

Two-Speed Motor Control Circuit: connects two electrically separate windings in different configurations, causing the speed to change from one rpm to another, with each winding delivering the motor's horsepower at a rated speed.

Overload Protection

Overload Protection: provided to protect the motor from excessive overheating due to a motor overload, protecting the motor from excessive loading and starter components and conductors from overheating.

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Description

Test your knowledge on motor control circuits with questions about wire control sequences, reversing circuits, and jog type circuits. Learn about how to start, stop, and change the direction of three-phase motors using different control methods.