AC Electric Motors Flashcards
In a single phase motor, how do we initially start the motor?
Do this by creating a rotating magnetic field. This is done by creating a phase difference between the main field windings and the starter field windings.
What is a split phase motor?
This is a motor that uses resistivity to create a phase difference. It does this by having a high resistivity in the field windings.
At what speed will the centrifugal switch open thus removing the starting windings from the main circuit?
75-80% of the synchronous speed.
How do we create a phase gap in the split phase motor?
Have a highly resistive auxiliary winding. Resistance follows voltage, so it is only a small angle behind the voltage phase. The main windings are highly inductive, which means it is a large angle behind the voltage phase. This difference will create a resultant current that will create a magnetic field.
What is a capacitor starter motor?
It is the same as a split phase in that it starts the motor by creating a phase difference, although it uses capacitance instead of resistance to create this phase difference.
Why do capacitor starter motors have such a large torque?
Because capacitance will lead the voltage, while the inductance of the main windings will lag the voltage. This will create a phase angle of nearly 90. Torque is proportional to this phase angle so we have a large starting torque.
What is a shaded pole motor?
It is a simple cheap motor that has a coil of wire and then a single copper wire as its two main windings.
What is a stepper motor?
A DC motor that rotates in steps.
What determines the speed of rotation of the rotor within the stepper motor?
The rate of electrical pulses that is sent to the rotor.
What are the main components of the stepper motor?
It consists of a rotor that is generally a permanent magnet. It then also has a stator that is usually a coil of wire.
What is the working principle of a Stepper Motor?
The current is able to change direction within the stator. This will change the magnetic properties of the winding and so the stator will either attract or repel the rotor which will result in a stepping motion.
What is a Universal Motor?
A motor that can run on either AC or DC, it is often referred to as an AC series motor.
What is the structure of a Universal Motor? Why do we wind the stator and armature in series?
It is a lot like a DC motor, except it has a laminated iron core to reduce eddy currents that come from the continuous reversal of the current. We wire the stator windings and the armature in series to ensure that if we do supply it with AC, then the current in the armature and the stator will change at the same time so we will get continuous rotation and unidirectional torque.
What are the characteristics of the Universal Motor?
It has a high starting torque and speed.
It is lightweight and compact.
What are the applications of the Universal Motor?
Portable power tools and household appliances.
