EE361-Electromechanical Energy Conversion

class: center, middle

# EE-361
# DC Machine Types

## Ozan Keysan

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

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

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# Review: 
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Induced Voltage in Armature

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## \\(E\_a = K\_a \omega\_m \Phi\_{pp}\\)
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- ### \\(E\_a\\): Induced armature voltage (DC-average)
- ### \\(K\_a\\): Armature Constant
- ### \\(\omega\_m\\): Mechanical Speed (rad/s)
- ### \\(\Phi\_{pp}\\): Flux per-pole (DC-average)

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# Equivalent Circuit of a DC Motor

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## If \\(V\_a > E\_a\\) motoring action
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## If \\(E\_a > V\_a\\) generating action
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# Torque Relation

## \\(P\_{mech} = T \omega = E\_a I\_a   \\)
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## \\( T \omega = K\_a \omega \Phi\_{pp} I\_a \\)
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## \\(T =K\_a  \Phi\_{pp} I\_a \\)
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# DC-Machine Equations

- ## Induced Voltage Proportional to Speed
## \\(E\_a = K\_a \omega\_m \Phi\_{pp}\\)
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- ## Torque Proportional to Armature Current
## \\(T =K\_a  \Phi\_{pp} I\_a \\)
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#Power Flow in a DC Motor
<img src="http://blogs.itb.ac.id/el2244k0112211027gemarizaldi/files/2013/04/shuntppwerflow.png" alt="Drawing" style="width: 600px;"/>
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## What about a generator?
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# Efficiency
## \\(\eta = \dfrac{P\_{out}}{P\_{in}}\\)
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## Efficiency of a DC Motor
### \\(\eta = \dfrac{P\_{mech}}{P\_{elec}}\\)
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\\(=\dfrac{T\_m \omega\_m}{V\_t I\_a}=\dfrac{T\_m \omega\_m}{T\_m \omega\_m + Losses} \\)
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# Efficiency
## \\(\eta = \dfrac{P\_{out}}{P\_{in}}\\)

## Efficiency of a DC Generator
### \\(\eta = \dfrac{P\_{elec}}{P\_{mech}}\\)
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\\(=\dfrac{V\_t I\_a}{T\_m \omega\_m}=\dfrac{V\_t I\_a}{V\_t I\_a + Losses} \\)

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# DC Machine Types
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## Everthing is same just different ways of connecting the field winding!
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<img src="images/dc_machine_types.jpg" alt="Drawing" style="width: 800px;"/>

### As a result \\(\Phi\_{pole} \\) is not constant but a function of field current.

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<img src="images/dc_machine_types.jpg" alt="Drawing" style="width: 800px;"/>

## - Series Excited
## - Shunt Excited
## - Compound Machines
## - Separately Excited

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# Separately Excited DC Machines

### Field is excited with a separate source
### Flexible Control (Field Current controls \\(\phi\_{pp}\\))

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# Magnetization Characteristics
## What is the relation between \\(I_f\\) and \\(E_a\\)?
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![](http://www.electrical4u.com/wp-content/uploads/2013/10/magnetic-curve-of-dc-generator-25.10.13.png)

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#Magnetization Characteristics
### In the Linear Region

## \\(\phi = K_f I_f\\)
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### Induced Voltage
## \\(E_a = K_a \omega_m \phi = K_a \omega_m K_f  I_f\\)
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### Torque
## \\(T = K_a K_f I_a I_f\\)
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## We have a motor running at constant speed under constant load.
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## What happens if we suddenly increase the load?
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#Speed Regulation
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## Speed Regulation \\(=\dfrac{\omega\_0 - \omega\_{rated}}{\omega\_{rated}}\\)

- ### \\(\omega_0\\) : Rotational Speed at no-load
- ### \\(\omega\_{rated}\\) : Rotational Speed at full load

####(Note the similarity with the voltage regulation in transformers)
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# Now let's operate as a generator
## Constant mechanical power, constant speed.
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## What happens if we increase the electrical load (armature current)?
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# Separately Excited DC Generator
## Vt-Ia Characteristics

<img src="http://nuclearpowertraining.tpub.com/h1011v2/img/h1011v2_92_1.jpg" alt="Drawing" style="width: 600px;"/>
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# Voltage Regulation

## Terminal voltage difference from no-load to full-load

#\\(=\dfrac{V\_{t(no-load)} - V\_{t(full-load)} }{V\_{t(full-load)}}\\)

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#Armature Reaction
### What happens to the airgap magnetic field if a current applied?

## Increases at the upper portion, decreases at the lower portion

## Flux density distribution is distorted.

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## Armature Reaction
## Becomes significant with increasing \\(I_a\\)

#Armature Reaction
## Becomes significant with increasing \\(I_a\\)

#Armature Reaction
### Armature reaction can be neglected at small \\(I_a\\)

###  \\(\phi\_f = \dfrac{MMF}{\mathrm{R}\_{eq}}= \dfrac{N\_fI\_f}{\mathrm{R}\_{eq}}\\)

### With armature reaction

### \\(\phi\_f = \dfrac{N\_fI\_f - N\_a I\_a}{\mathrm{R}\_{eq}}\\)
### Thus, \\(E_a\\) reduced due to increasing \\(I_a\\)

### - Vt-Ia Characteristics?

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# Shunt Wound DC Machine

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<img src="http://electriciantraining.tpub.com/14177/img/14177_29_1.jpg" alt="Drawing" style="width: 400px;"/>

## Field winding is connected in parallel to the Armature
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## \\(V_f=V_t\\) 
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==> \\(I_f = V_t/R_f\\)
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# Shunt Motor

## Shunt motor has good speed regulation
###(5-15% difference from no load to full load)
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# Shunt DC Generator
## Can we start generating voltage without any external source(i.e. self-excitation)?
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<img src="http://4.bp.blogspot.com/-2LzEQAU5wjk/TePx5d9UEaI/AAAAAAAAABI/ESfExlaYVFU/s320/10.JPG" alt="Drawing" style="width: 500px;"/>
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# Shunt DC Generator
## Self-Excitation only occurs if Rf is low enough
<img src="http://3.bp.blogspot.com/-Kp4Jzkv5uk4/TePyi8Nd1eI/AAAAAAAAABM/yKX0knuhhuA/s320/11.JPG" alt="Drawing" style="width: 500px;"/>
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#Shunt DC Generator
## \\(V_t\\)-\\(I_L\\) Characteristics
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<img src="http://www.scrigroup.com/files/limba/engleza/electronics/63_poze/image046.jpg" alt="Drawing" style="width: 500px;"/>
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# Series Wound DC Machine

## Field winding in series with armature

## Field current = Armature Current  ==> \\(I_f = I_a\\)
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# Series Wound DC Machine

## What happens if AC is applied to series DC motor?
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# Universal Motor

## Series DC motors work both with DC and AC

## [Universal Motor](https://www.youtube.com/watch?v=0PDRJKz-mqE)

[More Information](https://en.wikipedia.org/wiki/Universal_motor)

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# What is the origin of AC/DC band's name?

## [Highway to Hell](https://youtu.be/gEPmA3USJdI?t=89)

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<img src="images/ee361/singer.jpg" alt="Drawing" style="width: 800px;"/>

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# Series Wound DC Motor

### \\(V\_t = E_a + (R\_a + R\_f) I_a\\)
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### \\(E_a = K_a \omega_m \phi \\) ==> \\(\phi = K_s I_a\\)
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### \\(T_e = K_a \phi I_a = K_a K_s I_a^2\\)

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# Series DC Motor

## Never run a series DC motor at no load!

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# Series DC Motor

## Torque increases with the square of the armature current
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# Series DC Motor

### High starting torque
### Applications: Traction motors,cranes, 
### At no load speed increases dangerously

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# Series DC Generator

### Not suitable to be used as a generator as the voltage regulation is very bad.

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# Compound DC Machines

## Shunt and Series windings combined together
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### Series winding can be additive(more common) or subtractive
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# Compound DC Generators

### Commonly adjusted to be flat compounded, thus to achieve zero voltage regulation.
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# Example:
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## A 10 kW DC Shunt motor connected to 200 V supply and driving a load with the following characteristics.

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## \\(P_l = k n^2 = 3.9\;10^{-3} n^2\\) (n: speed in rpm)
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## Friction losses of the motor are constant and equal to 250 W.
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## Field winding is \\(40\;  \Omega\\),

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## a) Calculate the motor speed if the motor is supplying rated power from its shaft at steady state.
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## b) Determine the armature current and armature resistance  of the motor at rated load.

## Induced voltage vs. field current characteristics obtained at 1500 rpm are as follows:

## <table>
  <tr>
    <th>Ea(V) </th>
    <th>153.7 </th>
    <th>161.8 </th>
    <th>164.8 </th>
    <th>170.2 </th>
    <th>175 </th>
    <th>178.3 </th>
  </tr>
  <tr>
    <td>If(A)</td>
    <td>2</td>
    <td>3</td>
    <td>3.3</td>
    <td>4</td>
    <td>5</td>
    <td>6</td>
  </tr>
</table>
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## c) Calculate the total current drawn from the terminals and motor efficiency

<!-- 
d) If the shaft speed is measured as 1700 rpm, when the armature current is 54.8 A;

## i) Calculate the generated voltage (neglect armature reaction),

## ii)Calculate the generated voltage with armature reaction (refer to magnetization curve),

## iii) Calculate the extra field current supplied to compensate the armature reactance
-->

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# Summary

### All DC machines have same equations;
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but different field winding connections give different characteristics.
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## DC Machine Types
### - Separately Excited
### - Shunt Excited
### - Series Excited
### - Compound Machines

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## You can download this presentation from: [keysan.me/ee361](http://keysan.me/ee361)