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Electrical Machines Theory Period 4 SAIT-Alberta > Single Phase Motors > Flashcards

Flashcards in Single Phase Motors Deck (17)
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1

Where are most single phase motors found?

Rural and residential applications.

2

What is the typical efficency rating of a single phase motor?

60%.

3

How does a resistance split phase motor operate?

By using two stator windings of differing resistance and inductance to create an out of phase magnetic field rotation.

{Sometimes called a resistance start motor}

4

What are most resistance split phase rotors constructed of?

Cast aluminum squirrel cage around a laminated core.

5

What are three methods of start winding cut out?

Centrifugal switch;

Current sensitive relay;

Triac (electronic switch).

6

What is the typical displacement of the main and start winding currents in a resistance start motor?

25 to 30 degrees.

7

When do the centrifugal switch contacts open?

75% of rated speed.

8

How does a single phase motor operate when the start winding is cut out?

By cross field theory.

9

How many poles do most split phase motors have?

4.

10

What is the most common size of split phase motor?

1/4 hp.

11

What does reversible mean?

Direction of rotation can be changed at a standstill.

12

What does reversing mean?

Able to change direction of rotation in the run condition.

13

What are five common uses of resistance split phase motors?

Forced air furnace;

Washing machine;

Small drill press;

Fan;

Sump pump.

14

Why do split phase motors have such a low starting torque?

Because the winding currents only differ by roughly 30 degrees.

15

What are typical capacitance values for a 1/2 hp 2 value capacitor motor?

300 uf start;

40 uf run.

16

Is speed control acheivable with a 2 cap motor?

No.

17

What are some typical applications of 2 capacitor motors?

A/C unit compressor;

Submersible pump;

Refrigeration compressor.