Single-Phase motors
How many watts are equal to one horsepower?
746
A centrifugal switch in a single-phase split-phase motor opens when the rotor reaches approximatly _____ % of full speed.
75
In a capacitor-start induction-run motor, the capacitor causes the current in the start winding to lead the applied voltage, resulting in a _____° angle of displacement between the start and run winding currents.
90
How is the direction of rotation of single-phase split-phase motors determined?
From the back of the motor
What are the three main types of single-phase split-phase motors?
Resistance start induction run Capacitor start induction run Capacitor start capacitor run
What is the principal of operation of all three-phase motors?
Rotating magnetic field
What is the principal of operation of single-phase split-phase motors?
Rotating magnetic field
What are the three types of DC machines?
Series Shunt Compound
What type of rotor does the single-phase shaded pole motor have?
Squirrel Cage
What type of rotor does the single-phase split-phase motor have?
Squirrel cage
How is the direction of rotation of three phase motors reversed?
Switching any two stator leads
How is the direction of rotation of DC motors reversed?
Switching the armature leads
How is the direction of rotation of a single-phase universal motor changed?
Switching the armature leads
When interpreting motor nameplate information, what does Service Factor indicate?
The amount of short term overload a motor can handle
How is the start winding of a non-hermaticaly sealed single-phase split-phase motor generally disconnected?
The centrifugal switch
What two factors determine the speed of a single-phase split-phase motor?
The number of stator poles The frequency of applied voltage
What three factors determine the starting torque of a single-phase split-phase motor?
The strength of the magnetic field of the stator The strength of the magnetic field of the rotor The phase angle difference between the start windings and the run windings
Why should one NEMA design induction motor not be replaced with any other NEMA design?
They have different operating characteristics
What is the purpose of the centrifugal switch in a single-phase split-phase motor?
To disconnect the start winding when the motor reaches a certain RPM
Although not very common, how can the direction of rotation of a single-phase shaded-pole motor be changed?
Turn the stator around
How is the start winding of a hermetically sealed single-phase split-phase motor generally disconnected?
An external starting relay
Motors are generally designed to operate within _____% of the nameplate voltage.
10
The voltages of a three-phase system are _____° apart.
120
In a dual voltage single-phase split-phase motor connected for high voltage operation, the two sets of run windings will be connected in __________ as well as the start windings.
Series
In a dual voltage single-phase split-phase motor connected for low voltage operation, the two sets of run windings will be connected in __________ as well as the two sets of start windings.
Parallel
In a resistance-start induction run motor, a phase angle difference of 35°-40° is produced between the run winding current and the start winding current uring the starting period. The result is a __________ torque.
Poor starting
Are single-phase shaded pole motors induction motors?
Yes
Name some examples where single-phase shaded pole motors are used.
Exhaust Fans Small Blowers
The voltages of a two-phase system are ____° apart.
90
Define motor:
A device that converts electrical energy into mechanical energy.
What is the purpose of three capacitors connected in parallel to a three-phase induction motor?
Power factor correction
Define Generator:
A device that converts mechanical energy into electrical energy.
Some capacitor-start capacitor-run motors use a second capacitor during the starting period to improve starting torque. When this second capacitor is used, it is generally a _________________ type and is disconnected by a centrifugal switch or a potential starting relay.
AC Electrolytic
What type of Capacitors are used in the start windings of single-phase split-phase motors?
AC Electrolytic
If a capacitor is to be replaced in a capacitor-start induction-run motor, why is it very important to use the correct microfarad rating?
An incorrect microfarad rated capacitor might hamper the starting characteristics by altering the phase angle difference.
How is the direction of rotation of single-phase split-phase motors reversed?
By reversing the start winding leads or the run winding leads, but not both
What is one of the main differences between a single-phase series AC motor and a series DC motor?
Compensating Windings
What would happen if the start winding of a resistance-start induction-run motor was not disconnected?
It would burn up
What is the standard color code for a three-phase 208V system?
L1 Black L2 Red L3 Blue
What is the standard color code for a three-phase 480V system?
L1 Brown L2 Orange L3 Yellow
Do capacitor-start induction-run motors have higher running torque than resistance-start induction motors?
No
Does a single-phase series AC motor have a comparatively low starting torque?
No
Does a single-phase shaded pole AC motor have a comparativly high starting torque?
No
do squirrel cage rotors recieve current from the line through brushes?
No
Do all single-phase motors operate on the principal of rotating magnetic field?
Not all, but most.
What type of Capacitors are used in the run windings of single-phase split-phase motors?
Oil Filled
How are the start and run windings of a single-phase split-phase motor connected in relation to each other?
Parallel
Single-phase universal motors are used where light weight and high horsepower are needed. Name some examples.
Power Tools Vacuum Cleaners
What is the most common type of single phase motor that can be used with both AC and DC sources?
Universal
When is maximum starting torque developed between in a single-phase split-phase motor?
When the start and run currents are 90° out of phase
How is the run winding of a resistance-start induction-run motor constructed?
With a thick wire having a low resistance
How is the start winding of a resistance-start induction-run motor constructed?
With a thin wire having a high resistance
What are the three types of three-phase motors?
Wound rotor induction Squirrel cage induction Synchronous