Single phase motors (6hr)

How does a centrifugal switch work When does its contacts open

Is actuated by the centrifugal force produced by the spinning rotor. At 75% of rated speed of the motor

The main (run) windings are made of ______ insulated copper conductors mounted where.

Larger In the bottom of the stator slots

Why is a two value cap motor sought after

Low nosie, high starting torque, good power factor

What's the formula for synchronous speed

Ns = f x 120 / p

In order for a split phase motor to start, the current in the start winding must be:

Out of phase w/ the current in the main winding

In a resistance split phase motor the start (aux) winding is connected in _______ with the run winding & is wound w/ _____ turns of smaller insulated conductors What's it's value of resistance and inductance compared to the run winding

Parallel Fewer Higher resistence Lower reactance

Why is the oil filled cap left in operation during run conditions

Provides excellent run conditions (Power factor correction)

What's the difference between reversible and reversing

Reversible - direction of rotation can be changed while NOT moving Reversing - direction of rotation can change while in run condition

In a resistance start split phase motor. Which winding is made with larger insulated conductors w/ more turns & is mounted in the bottom of the stator slots.

Run winding

What additional means is required to produce the rotating magnetic field to develop starting torque in a single phase motor

Start winding

The four basic parts of a resistance split phase motor are

Stator Frame Rotor Centrifugal switch

Single phase split phase induction motors are classified by:

The way the stator windings are used for starting & runnning

The start windings of split phase motor are placed in the _____ of the stator slots, _______ & straddling the main windings

Top Over (on top)

While a resistance split phase motor is running ( after the centrifugal switch has operated) the cross field effect results in the motor simulating a

Two phase rotating magnetic field of 90 degrees displacement

Is a two value cap motor reversible

Yes. Interchange T5 & T8 start winding

Can a resistance split phase motor start in either direction.

Yes. Rotation can be reversed by interchanging the leads of the start OR run winding

In a single phase motor the run winding by itself produces a ______ magnetic field

Pulsating

What is two value cap motor used for

Air conditioning, sump pumps, refrigerators. In any high HP application over 7.5HP

The ______ winding of a split phase motor, is made of smaller conductors w/ fewer turns, has greater resistance &a less reactance the the ______ winding

Auxillary (start) Main (run)

What is another common name for the two value capacitor motor

Cap start or cap run

A resistance split phase motor has starting current & torque that are how much greater the running value

Current 5 - 6 times more Torque 125 - 150% more

What are the three main components of a two value capacitor motor

Cut out switch (centrifigul switch) Start capacitor (electrolytic 300 uf) Run cap ( oil filled 40uf)

What are common applications of resistance split phase motors

Fans ,washing machines, sump pumps, small drill press, furances

A resistance split phase induction motor has what values of starting torque and current (high or low)

High current Low torque

What are three ways the start winding of split phase motor can be controlled

1) centrifugal switch 2) current sensitive relay (high inrush current pulls in the current sensitive relay and the NO contacts close, energizing the start winding) 3) electronic switching (triacs)

The classification of split phase motors are which 4

1) resistance split phase motor (split phase) 2) capacitor start motor 3) permanent split capacitor motor 4) two value capacitor motor (capacitor start)

Most single phase motors fall into which range of HP

1/6 to 3/4 hp

The most common type of single phase motors induction motors are motors that use ______ sets of stator windings?

2

A single phase motor w/ _____ stator windings uses windings with different values of ____ & ___ to create a phase angle between the two currents in the stator. This is called a ____ start motor

2 Resistance & inductance Resistance

The typical displacement between start & main winding current in the resistance split phase motor is

25 - 30 degrees

What's the speed regulation of a resistive start induction motor? What is its typical slip?

4 - 6 % speed reg Slip 5%

Most single phase motors have efficiency ratings of?

60 - 68%

The start winding of a two pole split phase motor has the centre of the start windings placed how far from the main winding? What about for a four pole motor

90 degrees 45 degrees