EE568-Selected Topics in Electrical Machines

< EE568-Selected Topics in Electrical Machines

class: center, middle

# EE-568 Selected Topics in Electrical Machines

## Losses & Thermal Design

## Ozan Keysan

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

Office: C-113 <span class="meta">•</span> Tel: 210 7586
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# Losses in an Electrical Machine
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# Losses in an Electrical Machine
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- ## Stator Ohmic Losses
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- ## Rotor Ohmic Losses (or field excitation)
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- ## Core losses (hysteresis & eddy)
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- ## Additional eddy losses (rotor surface, magnets, sleeves etc.)
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- ## Mechanical losses (bearing, windage etc.)
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- ## Stray Losses (leakage flux induced losses)

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## Factors effecting core losses
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## Material Quality and Thickness

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## Factors effecting core losses

## Lamination cutting techniques

- ### Stamping,  Laser Cutting etc.

- [High Speed Laser Cutting](https://www.youtube.com/watch?v=7-M6pgUO5XE)

- [Lamination Stamping](https://www.youtube.com/watch?v=s-9PhX6vKpI)

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## Factors effecting core losses

## Fixing Stacking Together

- ### Riveting
- ### Welding

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## Losses: End Plate Losses

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## Losses: Press Plate Losses

## Stepped laminations at the press plate , but why?

<img src="./images/ee564/endplate2.png" alt="Drawing" style="width: 600px;"/>
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## Losses: Press Plate Losses

### Axial component of the fringing flux creates eddy current on large surfaces

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## Losses: Press Plate Losses

### Methods to reduce press plate losses:

- ### Partitioning of end plates
- ### Slitting of press fingers 
- ### Non-magnetic press plates (Aluminium, stainless steel) 
- ### Stepping of end packet
- ### Laminated glued press plates 
- ### Copper shielding

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## Rotor Pole Shoe Losses

- ### Especially dominant in open-slots

- ### Magnitude may be small, but the frequency is in the kHz range!

- ### \$f= f_s \times Q \$

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## Rotor Pole Shoe Losses

### Methods for reduction:

- ### Use [magnetic slot wedges](https://www.spindustries.at/product/magnetic-slot-wedges/)

- ### Laminated pole shoes, sectioned poles (or magnets in a PM machine)

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## Stray Field Losses

<img src="./images/ee564/stray_field.png" alt="Drawing" style="width:550px;"/>
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# 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}}\$

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# Skin Effect
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### AC current tends to flow close to surface (valid for a conductor surrounded by air).
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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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<img src="http://www.anttilehikoinen.fi/wp-content/uploads/2017/03/2017-3-2_skin_effect_slot-139x300.png" alt="Drawing" style="width: 200px;"/>
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# Leakage Flux in Slot

### Leakage flux density increases in the direction of slot opening
### That leakage flux is pulsating with fundamental frequency, and creates eddy currents (into the page)
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# Eddy Current in a Slot

### Direction of the eddy current creates a field opposite to the original field (Lenz Law)

### Eddy current increases the current density at the top of the conductor, causes non homogeneous current distribution

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# Eddy Current in a Slot

### Current also reduces the leakage flux on the top of the winding, and hence reduces the leakage flux component

### Therefore, \$R\_{ac} \gt R\_{dc}\$ but 
### \$L\_{leakage-ac} \lt L\_{leakage-dc}\$

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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

<img src="http://www.anttilehikoinen.fi/wp-content/uploads/2017/03/2017-3-2_circulating_current.png" alt="Drawing" style="width: 800px;"/>
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# Ways to Reduce AC Resistances

### Just using parallel wires DO NOT cancel the circulating currents

### Twisting is also required!

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## Twisting (or Transponding)

### In a single layer winding all the flux can be cancelled,
### but in double layer winding, the flux on the top and bottom portion are different, so that reduces but does not eliminate all current

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## Twisting (or Transponding)

### Overhang connections can be used for twisting

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# Roebel Winding

### [Roebel Winding Manufacturing](https://www.youtube.com/watch?v=TaM3EuTMxBs)
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# Roebel Winding

### With 180 degrees transposition
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# Roebel Winding

### With 360 degrees transposition

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# Roebel Winding

### End winding connection options

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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