2677322 Busbar Design

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David Chapman

Copper Development Association

[email protected]


Busbar Design Basics

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High electrical conductivity

only silver is better than copper

Good thermal conductor

heat reaches surface quickly

Strong (at working temperature)

to withstand short circuit stresses

low creep

Easy to joint

resistant to corrosion

Materials for Busbar Systems

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Busbar System Current Ratings

usbar ratings are determined only by the

ma!imum desired working temperature

"t working temperature#

heat generated $ heat lost

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usbar ratings depend on#

% &orking and ambient temperatures

% Heat lost from the busbar

' by convection

' by radiation

% Heat generated in the busbar

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25.0

25.166.7

v

Pcv

=

ower dissipated by convection is given by#

where

is the temperature rise above ambientv is the vertical height of the surface


Pcv1Pcv2 v

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Power dissipation per metre length v Vertical height

0

40

80

120

160

0 50 100 150 200

Vertical height (mm

Powerdissipationpermetrelength(!

onvection (for *+ temperature rise)


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Power dissipated by radiationis given by

84

1

4

2 107.5

= TTP

r

wherer is the power dissipated per square metre

,-is the working temperature. /,0is the ambient temperature. /

is the emissivity


Pr

Pr

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,he emissivity. . describes how effectivelythe surface radiates heat

1or a perfectly polished surface. the value is

close to 2ero 3 a very poor radiator

1or a matt black surface. the value is close to0 3 a very good radiator


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right copper has an emissivity of about +40

5uring use. the emissivity of the coppersurface increases 3 and the current rating

increases 3 as the copper darkens to reach anemissivity value of about +46

,in plated copper has an emissivity of about+47 to +48

ut painting bars reduces the current rating9


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Pr

Pr

Pr

Pr

Pr Pr

!o radiation heat loss

"rom internal sur"aces

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"adiation power dissipation v !or#ing temperat$re

0

20

40

60

80

100

2%& &2& &%&

A'sol$te !or#ing emperat$re ()

Powerdissipation(!p

ers*m

:adiation (for 7+ ambient)


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for 0++ mm vertical height. 7+ ambient

otal power dissipation v !or#ing temperat$re

0

100

200

&00

400

500

600

%00

800

+00

1000

40 60 80 100 120 140

!or#ing temperat$re (C

Powerdissipation

(!p

ers*

Convection

"adiation

otal


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RIP 2

=

a

lIP 2

=

,he power generated by current in the busbar is#

where

is the resistivity of the material

a is the cross sectional area

l is the length


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"t some temperature. the heat generated in the

busbar is equal to the total heat lost by convection

and radiation4

[ ] [ ]rci

PPP +=


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alculation method#

0 Select working and ambient temperatures

- "ssume initial current density of * amps;mm-

7 1ind appropriate si2e in standard range

< alculate heat generated due to current

8 alculate heat loss at working temperature

= >f

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,he most economicsi2e gives the lowest

lifetime cost4 >t is the minimum total cost of

%material

%installation and

%energy costs

over the circuit lifetime4

Higherpurchase cost 3 lowerrunning costs

Best economic sizing

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Cost o, 'ar

0

5

10

15

0 100 200 &00 400 500 600

Cross sectional area (s*mm

Costo,'arpermetre(-

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Cost o, losses . 5 /ears

0

10

20

&0

0 100 200 &00 400 500 600


Costo,lossesover5/ears(-

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Economic Sizing of Busbars

otal cost . 5 /ears

0

10

20

&0

0 100 200 &00 400 500 600


0i,etimecostp

ermetre(-

Cost o, 'ar

Cost o, loss

otal

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Busbar calculation software

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Further considerations

Having calculated the si2e of the bar. there

are three further considerations# voltage drop

skin effect

' increases apparent resistance by reducing

effective area 3 important for#

thick busbars

high frequencies

harmonics generated by non3linear loads

short circuit current

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Summary of Busbar Material Characteristics

High onductivity

% low loss. low voltage drop

% ?0+048 A >"S

Easy 1ormability

% due to small grain si2e and advanced production

technology% easy to bend without surface deformation

Good 1latness

% simple reliable jointing

Good Straightness

% easy installation. lower joint stress

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David Chapman


[email protected]


Documents

2677322 Busbar Design