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Questions and Answers
What is the purpose of the control circuit in a two-speed motor?
What is the purpose of the control circuit in a two-speed motor?
What does the overload protection in a motor circuit primarily protect against?
What does the overload protection in a motor circuit primarily protect against?
How does the control circuit prevent plugging of the motor?
How does the control circuit prevent plugging of the motor?
What effect does connecting the motor windings in different configurations have on the speed?
What effect does connecting the motor windings in different configurations have on the speed?
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Why are there two electrically separate windings in the two-speed motor?
Why are there two electrically separate windings in the two-speed motor?
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How does the overload protection safeguard the starter components?
How does the overload protection safeguard the starter components?
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Why is plugging not allowed in a two-speed motor?
Why is plugging not allowed in a two-speed motor?
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What is the consequence of excessive overheating in a motor due to overload?
What is the consequence of excessive overheating in a motor due to overload?
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How does connecting both windings in series affect motor performance?
How does connecting both windings in series affect motor performance?
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What is the primary purpose of the overload protection in a motor circuit?
What is the primary purpose of the overload protection in a motor circuit?
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Why can the motor be reversed but not plugged in the anti-plugging circuit?
Why can the motor be reversed but not plugged in the anti-plugging circuit?
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How does connecting both windings in parallel affect a two-speed motor's performance?
How does connecting both windings in parallel affect a two-speed motor's performance?
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What is the consequence of excessive overheating in a motor due to overload?
What is the consequence of excessive overheating in a motor due to overload?
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Why are two electrically separate windings housed in a two-speed motor?
Why are two electrically separate windings housed in a two-speed motor?
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What effect does connecting the motor windings in series have on its performance?
What effect does connecting the motor windings in series have on its performance?
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How does the control circuit contribute to the protection of a two-speed motor?
How does the control circuit contribute to the protection of a two-speed motor?
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What happens when a motor is plugged according to the anti-plugging circuit?
What happens when a motor is plugged according to the anti-plugging circuit?
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How does connecting the windings in different configurations impact the two-speed motor?
How does connecting the windings in different configurations impact the two-speed motor?
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What is NOT allowed in a two-speed motor?
What is NOT allowed in a two-speed motor?
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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.
