Busbar Design

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David Chapman

Copper Development Association

[email protected]

Copper Development Association Copper Development Association

Busbar Design Basics

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

 High electrical conductivityHigh electrical conductivity

•• only silver is better than copperonly silver is better than copper



 Good thermal conductorGood thermal conductor

•• heat reaches surface quicklyheat reaches surface quickly



 Strong (at working Strong (at working temperature)temperature)

•• to withstand short circuit stressesto withstand short circuit stresses

•• low creeplow creep



 Easy to jointEasy to joint

•• resistant to corrosionresistant to corrosion

Materials for Busbar Systems

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Busbar System Current Ratings

Busbar ratings are determined only by the Busbar ratings are determined only by the maximum desired working temperature

maximum desired working temperature

At working temperature: At working temperature:

heat generated = heat lost heat generated = heat lost

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Busbar System Current Ratings

Busbar ratings depend on: Busbar ratings depend on:

•

• Working Working and and ambient ambient temperatutemperaturesres •

• Heat Heat lost lost from from the the busbarbusbar – by convection

– by convection – by radiation – by radiation •

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25 25 .. 0 0 25 25 .. 1 1

66

66 ..

7

7 v

v

P

cv cv

θ

= =

Power dissipated by convection is given by: Power dissipated by convection is given by:

where where

θ

θ is the temperature rise above is the temperature rise above ambientambient v is the vertical height of the surface

v is the vertical height of the surface

Busbar System Current Ratings

P P_cv1_cv1 P

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Power dissipation per metre

Power dissipation per metre length v Vertical heightlength v Vertical height

0 0 40 40 80 80 120 120 160 160 0 0 5500 110000 115500 220000 Vertical height (mm) Vertical height (mm) P P o o w w e e r r d d i i s s s s i i p p a a t t i i o o n n

p p e e r r m m e e t t r r e e l l e e n n g g t t h h ( ( W W ) )

Convection (for 80 C temperature rise) Convection (for 80 C temperature rise)

Busbar System Current Ratings

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Power dissipated by

Power dissipated by radiationradiation is given by:is given by:

8 8 4 4 1 1 4 4 2 2

10

7

7 ..

5

₋₋ _×_× −− = =

T

P

_r_r

_ε

where where P

P_rr is the power dissipated per square metreis the power dissipated per square metre T

T₂₂ is the working temperature, Kis the working temperature, K T

T₁₁ is the ambient temperature, Kis the ambient temperature, K εε is the emissivityis the emissivity

Busbar System Current Ratings

P P_r_r

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The emissivity,

The emissivity, εε, describes how effectively, describes how effectively the surface radiates heat

the surface radiates heat

For a perfectly polished surface, the value is For a perfectly polished surface, the value is close to zero - a very

close to zero - a very poor radiatorpoor radiator

For a matt black surface, the value is close to For a matt black surface, the value is close to 1 - a very good radiator

1 - a very good radiator

Busbar System Current Ratings

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Bright copper has an emissivity of about 0.1 Bright copper has an emissivity of about 0.1 During use, the emissivity of the copper

During use, the emissivity of the copper surface increases - and the current rating surface increases - and the current rating

increases - as the copper darkens to reach an increases - as the copper darkens to reach an emissivity value of about 0.7

emissivity value of about 0.7

Tin plated copper has an emissivity of about Tin plated copper has an emissivity of about 0.3 to 0.5

0.3 to 0.5

But painting bars reduces the current rating! But painting bars reduces the current rating!

Busbar System Current Ratings

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Busbar System Current Ratings

P P_r_r P P_r_r P P_r_r P P_r_r P P_r_r PP_r_r

No radiation heat loss No radiation heat loss from internal surfaces from internal surfaces

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Radiation power dissipation v Working temperature Radiation power dissipation v Working temperature

0 0 20 20 40 40 60 60 80 80 100 100 2 27733 332233 337733 Absolute Working Temperature (K)

Absolute Working Temperature (K) P P o o w w e e r r d d i i s s s s i i p p a a t t i i o o n n ( ( W W p p e e r r s s q q m m ) )

Radiation (for 30 C ambient) Radiation (for 30 C ambient)

Busbar System Current Ratings

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for 100 mm vertical height, 30 C ambient for 100 mm vertical height, 30 C ambient

Total power di

Total power dissipation ssipation v Working v Working temperaturetemperature

0 0 100 100 200 200 300 300 400 400 500 500 600 600 700 700 800 800 900 900 1000 1000 4 400 6600 8800 110000 112200 114400 P P o o w w e e r r d d i i s s s s i i p p a a t t i i o o n n ( ( W W p p e e r r s s q q Convection Convection Radiation Radiation Total Total

Busbar System Current Ratings

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R

I

P

₌₌ 22

a

l

I

P

₌₌ 22

ρ

The power generated by current in the busbar is: The power generated by current in the busbar is:

where where

ρ

ρ is the resistivity of the materialis the resistivity of the material

a

a _{is the cross sectional area}_{is the cross sectional area} l

l _{is the length}_{is the length}

Busbar System Current Ratings

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At some temperature, the heat generated in the At some temperature, the heat generated in the busbar is equal to the total heat lost by convection busbar is equal to the total heat lost by convection and radiation. and radiation.

[

[ ]

cc

] [

[ ]]

r r ii

P

₌₌ ₊₊

Busbar System Current Ratings

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Calculation method: Calculation method: 1

1 SSeelleecct t wwoorrkkiinng g aannd d aammbbiieennt t tteemmppeerraattuurreess 2

2 AAssssuumme e iinniittiiaal l ccuurrrreennt t ddeennssiitty y oof f 8 8 aammppss//mmmm22

3

3 FFiinnd d aapppprroopprriiaatte e ssiizze e iin n ssttaannddaarrd d rraannggee 4

4 CCaallccuullaatte e hheeaat t ggeenneerraatteed d dduue e tto o ccuurrrreenntt 5

5 CCaallccuullaatte e hheeaat t lloosss s aat t wwoorrkkiinng g tteemmppeerraattuurree 6

6 IIf f 44>>55, , iinnccrreeaasse e ssiizze e aannd d rreettuurrn n tto o 44 When 4=<5, this is

When 4=<5, this is smallest possiblesmallest possible sizesize

Minimum size calculation

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The

The most economicmost economic size gives the lowestsize gives the lowest lifetime cost

lifetime cost _._{. It}_{It is}_{is the}_{the minimum total}_{minimum total cost}_{cost of}_of •material

•material •

•installation andinstallation and •energy costs •energy costs

over the circuit lifetime. over the circuit lifetime.

Higher

Higher purchase cost -purchase cost - lowerlower running costsrunning costs

Best economic sizing

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Best economic sizing

Cost of bar Cost of bar 0 0 5 5 10 10 15 15 0 0 110000 220000 330000 440000 550000 660000 Cross sectional area (sqmm)

Cross sectional area (sqmm)

C C o o s s t t o o f f b b a a r r p p e e r r m m e e t t r r e e ( ( $ $ ) )

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Best economic sizing

Cost of losses - 5 years Cost of losses - 5 years

0 0 10 10 20 20 30 30 0 0 110000 220000 330000 440000 550000 660000 C C o o s s t t o o f f l l o o s s s s e e s s o o v v e e r r 5 5 y y e e a a r r s s ( ( $ $ ) )

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Economic Sizing of Busbars

Total

Total cost cost - - 5 5 yeye arsars

0 0 10 10 20 20 30 30 0 0 110000 220000 330000 440000 550000 660000 Cross sectional area (sqmm)

Cross sectional area (sqmm) L L i i f f e e t t i i m m e e

c c o o s s t t p p e e r r m m e e t t r r e e ( ( $ $ ) ) Cost of bar Cost of bar Cost of loss Cost of loss Total Total

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Busbar calculation software

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Busbar calculation software

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Busbar calculation software

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Further considerations

Having calculated the size of the bar, there Having calculated the size of the bar, there are three further considerations:

are three further considerations:

•• voltage dropvoltage drop

•• skin effectskin effect –

– increases apparent resistance by reducingincreases apparent resistance by reducing effective area - important for:

effective area - important for: ◊

◊ thick busbarsthick busbars ◊

◊ high frequencieshigh frequencies ◊

◊ harmonics generated by non-linear loadsharmonics generated by non-linear loads

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Summary of Busbar Material Characteristics

High Conductivity High Conductivity

•

• low loss, low voltage droplow loss, low voltage drop •

• >>110011..5 5 % % IIAACCSS

Easy Formability Easy Formability

•

• due tdue to smao small gll grain rain sizsize ane and advd advancanced pred produoductioctionn technology

technology •

• easeasy to y to benbend wid withouthout surt surface face defdeformormatioationn

Good Flatness Good Flatness

•

• simple reliable jointingsimple reliable jointing

Good Straightness Good Straightness

•

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David Chapman

Copper Development Association

[email protected]

Copper Development Association Copper Development Association