EE362-Electromechanical Energy Conversion-II

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# EE-362 ELECTROMECHANICAL ENERGY CONVERSION-II

# Single Phase Induction Motors

## Ozan Keysan

[keysan.me](http://keysan.me)

Office: C-113 <span class="meta">•</span> Tel: 210 7586

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# Single Phase Induction Motors
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## Remember Rotating MMF?

### We use three pulsating waves to create a traveling wave.

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# Single Phase Induction Motors
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### What would happen if there is only one phase in the stator?

## A pulsating flux density will be produced!

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# Pulsating MMF?

## \$\mathrm{F(\theta, t)} = F\_{max} cos (\omega t) cos (\theta\_e)\$

- ### \$cos (\omega t)\$: Time dependent component

- ### \$cos (\theta\_e)\$: Position dependent component

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# Pulsating MMF?

## A pulsating MMF can be separated into two components

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# Pulsating Wave

## Double rotating field theory?
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## A pulsating wave is addition of two waves moving in the opposite directions.

### [Wave Tank Experiment](https://www.youtube.com/watch?v=NpEevfOU4Z8), [Acoustic Levitation](https://www.youtube.com/watch?v=0K8zs-KSitc)

### [FloWave Edinburgh Univ.](https://www.youtube.com/watch?v=RHTcSKkUU8U), [Slow Mo Wave](https://www.youtube.com/watch?v=iWKFPTgkpXo)
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# Pulsating MMF?

## A pulsating MMF can be separated into two components

### $$ \mathrm{F(\theta, t)} = \dfrac{1}{2} F\_{max} cos (\theta\_e+ \omega t) $$
### $$+ \dfrac{1}{2} F\_{max} cos (\theta\_e - \omega t)$$

### \$\omega t\$: Forward rotating component

### \$-\omega t\$: Reverse rotating component

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# Single Phase Induction Motors

## There are two phasors moving in the opposite directions: [Animation](https://andymikeknight.github.io/machines/other/spim.html), [Animation-2](https://dspfirst.gatech.edu/chapters/02sines/demosLV/phasors/index.html)

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# Torque in a 3-phase Induction Machine

<img src="https://engineering.louisville.edu/raise/ECE252/images/L19-18.gif" alt="Drawing" style="width: 600px;"/>
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# [Torque](https://docs.google.com/spreadsheets/d/1YVq94hV64z6VSiN8q-v7XydcfLR3xLdcp-5GhdYZg6Y/edit?usp=sharing) in a Single Phase Induction Machine?

### Resultant torque of single-phase induction motor is zero at zero speed: Motor cannot self-start, we need some modifications.

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# What about two-phase configuration?

## Will it create a rotating MMF?

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# What about two-phase configuration?

## Will it create a rotating MMF?: YES

<!---
[Animation](http://www.ece.umn.edu/users/riaz/anim/dq_transformations.html)

<img src="https://i.stack.imgur.com/j0Cj7.gif" alt="Drawing" style="width: 600px;"/>
-->
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# Ok, two-phase winding can create rotating MMF but,
# how can you imitate two phase excitation, using a single-phase supply?

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# Split-Phase Motors

## Two orthogonal(\$\pi / 2 \$ electrical) windings:

## 1- Main (running) Winding: 
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## 2- Auxiliary (starting)  Winding:

- ### Higher resistance-to-reactance (R/X) ratio

- ### A thinner wire is used
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# Split-Phase Motors

### Unbalanced winding creates phase difference even if the same voltage is applied

[Split-phase machine animation](https://andymikeknight.github.io/machines/other/spim.html)
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# Split-Phase Motors

### Creates a net torque at start-up

<img src="./images/split_phase_torque.png" alt="Drawing" style="width: 550px;"/>
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# Centrifugal Switch

### Disconnects the axillary switch when the machine reaches 75% of \$\omega_s\$, from this point the machine is a single phase machine

[Electronic Centrifugal Switches](https://www.youtube.com/watch?v=xlXXXVflLuc)
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# Split-Phase Motors

- ### Moderate starting torque
- ### Low starting current
- ### Used in fans, pumps, office equipment