EE564-Design of Electrical Machines

class: center, middle

# EE-564 Design of Electrical Machines

# Resistances

## Ozan Keysan

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

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

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# Resistances
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## DC Resistance

### \\(R\_{dc}= \dfrac{l}{\sigma A}\\)

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# AC Resistance

### \\(k\_{Ru}=\dfrac{R\_{AC}}{R\_{DC}}\\)

# Resistances
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## DC Resistance

### \\(R\_{dc}= \dfrac{l}{\sigma A}\\)

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# AC Resistance

### Resistance factor: \\(k\_{Ru}=\dfrac{R\_{ac}}{R\_{dc}}\\)

<img src="https://raw.githubusercontent.com/ozank/ozank.github.io/master/presentations/images/coil.png" alt="Drawing" style="width: 300px;"/>
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# Critical Conductor Height

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# Skin Effect
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### AC current tends to flow close to surface
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### [Skin Effect](https://en.wikipedia.org/wiki/Skin_effect), [AC Resistance](https://www.youtube.com/watch?v=Cf80ZybFgoE)
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# Skin Effect

### Current Density distribution in [solid copper in a slot](http://www.anttilehikoinen.fi/technology/electrical-engineering/what-are-circulating-eddy-currents/)
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# Proximity Effect
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### Close conductors effect each other's current distribution
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### Conductors with the same current direction

### [Proximity Effect](https://circuitglobe.com/proximity-effect.html), [Skin and Proximity Effect](http://www.anttilehikoinen.fi/technology/electrical-engineering/what-are-circulating-eddy-currents/)
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# Proximity Effect

### Close conductors effect each other's current distribution

### Conductors with the opposite current direction

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# Proximity Effect

### Distribution in a slot (same winding)

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# Proximity Effect

### Distribution in a slot (same winding)

### Current Density distribution in [a copper winding in a slot](http://www.anttilehikoinen.fi/technology/electrical-engineering/what-are-circulating-eddy-currents/)
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# Proximity Effect

### Distribution in a transformer winding

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# Ways to Reduce AC Resistances
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- ### Divide conductors into subconductors
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- ### Instead of dividing large conductors and transposing them, use parallel paths
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- ## Use multi-thread twisted conductors (litz wire, roebel cable)

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# Circulating Currents

### Different leakage inductance, length, phase difference in induced voltage causes circulating current

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# Ways to Reduce AC Resistances

# Transponding
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### [Continuously Transposed Conductor](http://www.powertransformerdesign.net/2012/01/power-transformers-load-losses-basics.html)

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# Ways to Reduce AC Resistances

## Transponding
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### [Continuously Transposed Conductor](http://www.powertransformerdesign.net/2012/01/power-transformers-load-losses-basics.html)
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# Ways to Reduce AC Resistances
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## Transponding

### [Continuously Transposed Conductor](http://www.powertransformerdesign.net/2012/01/power-transformers-load-losses-basics.html)

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# Roebel Cable

### For very high frequencies, superconductors

[More info](http://www.itep.kit.edu/hts4fusion2011/downloads/1C3.pdf), [Transpositiion of conductors](http://www.electrotechnik.net/2011/10/transposition-of-conductors.html), [Transposition](http://en.wikipedia.org/wiki/Transposition_%28telecommunications%29), [Continuously Transposed Conductors](http://www.samdongamerica.com/products/ctc-continuously-transposed-conductor)

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# Ways to Reduce AC Resistances

# Litz Wire

[Types](http://www.newenglandwire.com/products/litz-wire-and-formed-cables/types-and-constructions), [Litz Wire Applications](http://www.litz-wire.com/applications.php), [Litz Wire theory](http://www.newenglandwire.com/products/litz-wire-and-formed-cables/theory)
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# Ways to Reduce AC Resistances

# Litz Wire

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# Insulation
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## Average dielectric strength: 1 kV/mil (~ 40 kV/mm)

#### (*)1000 mil = 1 inch
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## Stator should be insulated for:

- ### In-turn shorts
- ### Phase-Ground shorts
- ### Phase-Phase shorts

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# Insulation

<img src="https://raw.githubusercontent.com/ozank/ozank.github.io/master/presentations/images/insulation.png" alt="Drawing" style="width: 700px;"/>
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# Insulation

<img src="https://raw.githubusercontent.com/ozank/ozank.github.io/master/presentations/images/slot_insulation.png" alt="Drawing" style="width:600px;"/>
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# Slot Insulation Types

<img src="https://raw.githubusercontent.com/ozank/ozank.github.io/master/presentations/images/slot_insulation_types.png" alt="Drawing" style="width:750px;"/>
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# Insulation Temperature Class

- ## Class A: 105 C
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- ## Class B: 130 C
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- ## Class F: 155 C
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- ## Class H: 180 C

### Insulation life time halves for each 10 C rise in operating

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# Insulation

- ## PWM inverters cause voltage spikes or standing voltage waves

- ## PWM inverters can cause corona insulation faults

- ## Under 250 VAC, phase-to-phase insulation is not required

- ## For higher voltages end turns should be insulated

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# Slot Design

Ref: Tim Miller - Lecture 14
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# Slot Design

Ref: Tim Miller - Lecture 14

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# Common Faults in Windings
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: Good Winding