Unit 35
The windings of a three phase motor are:
120° apart
The start capacitor for fractional horsepower, open-type capacitor start motors is removed from the circuit by:
A centrifugal switch.
The start capacitor is removed from the circuit of a CSCR compressor by:
A potential starting relay.
The start capacitor is removed from the CSCR circuit by:
A starting relay.
The rotor consists of:
Aluminum bars mounted on a laminated soft iron core.
Why are capacitors rated at higher voltages than the unit line voltage?
Charging and discharging in series with an inductive load subjects them to high voltage.
Variable-frequency drives (VFD) reduce the speed of AC motors by:
Controlling the frequency (Hz) of the power to the motor.
The phase current of a wye-wound three phase motor is:
Equal to the line current:
The capacitor in a permanent split capacitor (PSC) motor:
Is in series with the start winding.
Compared to PSC motors, brushless DC motors:
More efficient and better suited for variable-speed applications.
AC induction motor speed is determined by the frequency (Hz) and the number of:
Motor poles.
The magnetic field of the stator is:
Opposite in polarity as the rotor magnetic field.
The rotor of an ECM motor is composed of:
Permanent magnets.
The most common type of single-phase motor used in HVACR equipment is:
Permanent split capacitor (PSC)
ECM motor speed is controlled by:
Pulses of DC power sent by the control module to the windings.
The run capacitor of a permanent split capacitor (PSC) motor:
Remains in the circuit while the motor operates.
The two principal parts of an AC induction motor are the:
Rotor and stator.
Compared to the run winding, the start winding is constructed of:
Smaller gauge wire than the run winding.
Compared to single-phase motors, three phase motors are:
Stronger starting with a higher operating efficiency.
When operated with the same power source, which induction motor will have a higher RPM: a four-pole motor or a six-pole motor?
The four-pole motor will turn faster.
The rotation of an ECM motor is determined by:
The module program.
What happens when a three-phase motor tries to operate on only two legs of power?
The motor overheats.
The speed of an AC induction motor is determined by:
The number of poles and the frequency of the alternating current.
The two electrical connectors on an ECM motor are:
The power connector and control connector.
The rotor turns because of:
The repulsion and attraction between the poles of the rotor and stator.
The part of an AC induction motor that turns is called:
The rotor.
Part of an Ac induction motor that induces the current flow in the rotor is called:
The stator.
A major difference between three-phase motors and single-phase motors is that:
Three-phase motors do not need ant type of starting components.
What is the primary purpose of the run capacitor?
To increase motor efficiency.
What is the primary purpose of the start capacitor?
To increase the motor starting torque.
The two common winding configurations for three-phase motors are:
Wye and delta.
The line current of a delta-wound three-phase motor is:
1.73 times the phase current.
The proper way to discharge a capacitor is to:
Connect a bleed resistor across the terminals.
To reverse the rotation of a three-phase motor:
Reverse any two power legs going to the motor.
A technician has installed a new three-phase motor, but it is running in reverse. What should she do to correct the rotation?
Reverse two motor power supply leads.
How does the rotor of an AC induction motor receive current?
Rotor current is induced by the rotor magnetic field.
This type of AC motor is characterized by low starting toque and is suitable for light applications such as refrigerator evaporator motors.
Shaded pole
The twisting force that must be developed by a motor to turn its load is called:
Torque
Compared to the stator's magnetic field, the rotor's magnetic field is:
opposite in polarity.