EE362-Electromechanical Energy Conversion-II

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# EE-362 ELECTROMECHANICAL ENERGY CONVERSION-II

# Starting Methods and Operating Modes of Induction Machines

## Ozan Keysan

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

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

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# Example

### A Y-connected 480 V(l-l), 50 hp induction motor is drawing 60 A at 0.85 pf lagging.

The stator copper losses are 2kW and the rotor copper losses are 700W.
 The friction and windage losses are 600 W, the core losses are 1800 W and the stray losses are negligible, find:

- ### The air gap power.

- ### The gross mechanical power.

- ### The net output power.

- ### The efficiency of the motor
-->
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# Induction Motors

## HMS Queen Elizabeth, Aircraft Carrier
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# Induction Motors

## 20 MW Induction Motor for [HMS Queen Elizabeth](https://en.wikipedia.org/wiki/HMS_Queen_Elizabeth_(R08)
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# Induction Motors

### Single Line Diagram of HMS Queen Elizabeth Power System

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#Typical Torque Curve of an Induction Motor

## [Torque Graphs](https://docs.google.com/spreadsheets/d/1YVq94hV64z6VSiN8q-v7XydcfLR3xLdcp-5GhdYZg6Y/edit?usp=sharing)

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# Maximum Torque Point

### \\(s\_{maxT}= \dfrac{r'\_2}{\sqrt{R\_{th}^2+ (X\_{th}+X'\_2)^2}}\\)

# Maximum Torque Point

### \\(T\_{max} = 3 \dfrac{ 0.5 V\_{th}^2}{\omega\_s}\dfrac{1}{(R\_{th}+\sqrt{R\_{th}^2 + (X\_{th}+X'\_2)^2}}\\)

# Maximum Power Point

### \\(s\_{maxP}= \dfrac{r'\_2}{r'\_2 + \sqrt{(R\_{th}+r'\_2)^2+ (X\_{th}+X'\_2)^2}}\\)

# \\(s\_{maxT} \ne s\_{maxP} \\)
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## What is wrong with directly connecting motor to a constant voltage supply (i.e. grid)?
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- ## High Start-up Current
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- ## Low(or high) Torque at Start-up

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# Starting Methods (Source Side):
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## 1- Use Auto-transformer (Variac)

### Apply a smaller voltage during start-up, and increase it gradually.

### Remember: Torque \\( \propto V^2 \\)
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# Starting Methods (Source Side):

## 2- Use (\\(Y - \Delta \\)) switch

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# Starting Methods (Source Side):

## 3- Soft Starters

[Soft Starters](https://www.youtube.com/watch?v=PjhhOgud4Lo), [Soft starter vs Motor Drive](https://www.youtube.com/watch?v=kX0LKxeIobc&list=PLuu0KknSI2tSmpnQjFdCKD0m0-4Jmyi79)

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# Starting Methods (Source Side):

## 4- Induction Motor Drives

### Variable Voltage-Frequency Source (or Variable Frequency Drives)

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# Starting Methods (Source Side):

## 4- Induction Motor Drives

### Variable Voltage-Frequency Source (or Variable Frequency Drives)

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# Starting Methods Comparison:

<img src="https://img1.daumcdn.net/thumb/R1280x0/?scode=mtistory2&fname=https%3A%2F%2Fblog.kakaocdn.net%2Fdn%2Fb891d5%2Fbtq5uHB9RpE%2FMzqD47s0ncSjU4QDEpOer1%2Fimg.png" alt="Drawing" style="width: 650px;"/>
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# Starting Methods (Machine Side):

## How to increase the starting torque, but reduce the starting current at the same time?
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### \\(s\_{maxT}= \dfrac{r'\_2}{\sqrt{R\_{1}^2+ (X\_{1}+X'\_2)^2}}\\)

### \\(T\_{max} = 3 \dfrac{ 0.5 V^2}{\omega\_s}\dfrac{1}{(R\_{1}+\sqrt{R\_{1}^2 + (X\_{1}+X'\_2)^2}}\\)

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# Starting Methods (Machine Side):

## Increase rotor resistance (\\(r'\_2\\))

#### [Torque Graphs](https://docs.google.com/spreadsheets/d/1YVq94hV64z6VSiN8q-v7XydcfLR3xLdcp-5GhdYZg6Y/edit?usp=sharing)

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# Starting Methods (Machine Side):

## Increase rotor resistance (\\(r'\_2\\))

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# How to modify (\\(r'\_2\\))?

## 1 - Add External Resistor
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: Easy for wound rotor induction motors by using external resistance

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# How to modify (\\(r'\_2\\)) for squirrel cage motors?
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## 2 - Use Deep Rotor Bars: Utilize rotor resistance change with skin effect
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# Rotor Bar Shapes

For curious students: [Rotor design](http://www.mhhe.com/engcs/electrical/chapman/fundamentals/ind_motor.pdf)
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# Complete Torque Characteristics

## Can slip be larger than 1, or can it be less than 0?

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### Full Operating Range of Induction Machines

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# Operation Modes of Induction Motors

# 1- Motoring

# 2- Generating

# 3- Braking (Plugging)

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# Motoring

## Slip: \\(0 < s < 1\\)

## Power Flow: Electrical to Mechanical

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# Generating

## Slip: \\(s < 0\\)

## Power Flow: Mechanical to Electrical

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# Braking (Plugging)
### Slip: \\(s > 1\\)

## Power Flow: Mechanical+Electrical to Heat

### Plugging obtained by interchanging two stator phases

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# Machine Dynamics

## Torque Balance Equation

## \\(T\_{elec} - T\_{load} = J \dfrac{d \omega}{dt} \\)

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### If there is no difference between the electrical torque and load torque, the machine operates at the steady-state

### (i.e. the intersection point at between the motor torque line and the load torque line).

### but beware of unstable intersection points.

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# Four-Quadrant Operation

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## You can download this presentation from: [keysan.me/ee362](http://keysan.me/ee362)