Single-Phase Motors Flashcards
In general, single-phase motors do not perform as well as three-phase motors of comparable horsepower. T or F?
True
What are the most common fractional horsepower sizes for single-phase motors?
1/6 to 3/4 HP
________ ________ Motors are classified by the way the two windings are used to start and run the motor.
Split-Phase Motors
Name the basic components of a resistance split-phase motor.
The stator
The rotor
The frame
The centrifugal switch
The stator winding consists of a laminated steel core with slots to hold the insulated windings. Describe the auxiliary winding.
The auxiliary (or start) winding is made of smaller conductors with fewer turns. It also has GREATER resistance and LESS reactance than the main winding.
The start winding of a four pole motor has the windings how many degrees away from the main windings?
45 degrees from the main windings
A centrifugal switch is mounted inside the motor and serves to disconnect the start winding when the motor nears full-speed. At what percent does the switch open?
75%
In a single-phase motor, the run winding by itself produces a rotating magnetic field. T or F?
False. The run winding produces a pulsating magnetic field, not the rotating magnetic field required to start the rotor turning.
In a resistance split-phase motor, what amount of degrees is the displacement between the main and starting windings?
Usually about 25-30 degrees
Describe the cross field theory.
The cross field theory is used to explain motor operation once the motor is running. When the rotor is turning, the currents flowing in the rotor circuit LAG the induced rotor voltage by about 80 degrees. This is because the rotor has very little resistance and comparatively high inductive reactance.
The starting torque of a resistance split-phase motor is around _____ to ______ of rated running torque.
125% to 150%
A common use of a resistance split-phase motor is a washing machine. T or F?
True
The resistance split-phase induction motor has what two starting characteristics?
Low starting torque
High starting current
The best performance from a split-phase, single-phase motor is provided by what type of motor?
Dual Cap Motor/Two-Value Capacitor Motor
What type of capacitor is connected to the RUN winding in a dual cap motor?
oil-filled continuous duty rated at 40uf
The electrolytic capacitor and the oil capacitor are connected in series. T or F?
False. They’re connected in Parallel
Two-Value Capacitor Motors are in-expensive, quiet, yet operate with a poor power factor. T or F?
False. They are the most expensive, quiet and operate with a good power factor.
Name the terminals of an integral thermal protection device and what components it contains
P1, P2 and P3
They contain a circuit breaking component between P1 & P2
A current sensing component (heater) between P2 & P3
And sometimes a manual reset. If manual reset is not found, its an automatic reset.
In regards to a high voltage connection for a dual voltage, reversible, thermally-protected, split-phase motor, what terminal connects to P3?
T1
In regards to a Low-voltage connection for a dual-voltage, reversible split-phase motor, what terminals are connected to L2?
T2, T4, and T8
Low-noise, high starting torque describes the characteristics of what split-phase motor?
Dual Cap Motor/Two Value Capacitor Motor
If you require 5-10hp motor you should probably just use what?
A 3ø Induction Motor
What does a centrifugal switch look like?
How does the start winding of a split-phase motor work?
Cross-field Theory
How many types of Split Phase Induction Motors are there?
4 Types
- Resistance Split Phase
- Capacitor Start
- Capacitor Run
- Capacitor Start/Run
What is the symbol for a centrifugal switch?
What do these symbols represent?
A Centrifugal Switch
Not finished yet. According to NEMA which end is the Front of a motor?
Non-Drive end. Or Non-shaft end.
Are Centrifugal Switches Normally-Open or Normally-Closed?
Normally Closed
What does the term Reversible mean?
Motor can run in reverse but needs to be stopped before changing direction
What does the term Reversing mean?
The motor can change direction while running.
Name 4 important characteristics of the START WINDING compared to the Main or Run winding in a Resistance-start split phase motor.
- Smaller Gauge Wire
- Less Turns
- Higher Resistance
- Lower Inductive Reactance
Resistance-Start….
Start Windings are bigger or smaller?
Smaller
Resistance-Start….
Run Windings are bigger or smaller?
Bigger
Resistance-Start….
Start Winding longer or shorter?
Shorter
