Answer Posted / rupesh usadadiya

Calculate Size of Bus bar having Following Details

Bus bar Current Details:
Rated Voltage = 415V,50Hz ,
Desire Maximum Current Rating of Bus bar =630Amp.
Fault Current (Isc)= 50KA ,Fault Duration (t) =1sec.
Bus bar Temperature details:
Operating Temperature of Bus bar (θ)=85°C.
Final Temperature of Bus bar during Fault(θ1)=185°C.
Temperature rise of Bus Bar Bar during Fault (θt=θ1-θ)=100°C.
Ambient Temperature (θn) =50°C.
Maximum Bus Bar Temperature Rise=55°C.
Enclosure Details:
Installation of Panel= Indoors (well Ventilated)
Altitude of Panel Installation on Site= 2000 Meter
Panel Length= 1200 mm ,Panel width= 600 mm, Panel Height= 2400 mm
Bus bar Details:
Bus bar Material= Copper
Bus bar Strip Arrangements= Vertical
Current Density of Bus Bar Material=1.6
Temperature Co efficient of Material Resistance at 20°c(α20)= 0.00403
Material Constant(K)= 1.166
Bus bar Material Permissible Strength=1200 kg/cm2
Bus bar Insulating Material= Bare
Bus bar Position= Edge-mounted bars
Bus bar Installation Media= Non-ventilated ducting
Bus bar Artificial Ventilation Scheme= without artificial ventilation
Bus bar Size Details:
Bus bar Width(e)= 75 mm
Bus bar Thickness(s)= 10 mm
Number of Bus Bar per Phase(n)= 2 No
Bus bar Length per Phase(a)= 500 mm
Distance between Two Bus Strip per Phase(e)= 75 mm
Bus bar Phase Spacing (p)= 400 mm
Total No of Circuit= 3 No.
Bus bar Support Insulator Detail:
Distance between insulators on Same Phase(l)= 500 mm
Insulator Height (H)= 100 mm
Distance from the head of the insulator to the bus bar center of gravity (h)= 5 mm
Permissible Strength of Insulator (F’)=1000 Kg/cm2

Untitled
Calculation:
(1) De rating Factors for Bus bar:

(1) Per Phase Bus Strip De rating Factor (K1):
Bus bar Width(e) is 75mm and Bus bar Length per Phase(a) is 500mm so e/a is 75/500=0.15
No of Bus bar per phase is 2 No’s.
From following table value of de rating factor is 1.83

Number of Bus Bar Strip per Phase (K1)
e/a No of Bus Bar per Phase
1 2 3
0.05 1 1.63 2.4
0.06 1 1.73 2.45
0.08 1 1.76 2.5
0.1 1 1.8 2.55
0.12 1 1.83 2.6
0.14 1 1.85 2.63
0.16 1 1.87 2.65
0.18 1 1.89 2.68

0.2
1 1.91 2.7



(2) Bus bar Insulating Material De rating Factor (K2)
Bus bar having No insulating material. It is Bare so following Table
De rating Factor is 1.

Bus Bar Insulating Material (K2): De rating Factor
Bare 1
PVC Sleeving 1.2
Painted 1.5



(3) Bus bar Position De rating Factor (K3)
Bus bar Position is Edge-mounted bars so following Table
De rating Factor is 1

Bus Bar Position(K3): De rating Factor
Edge-mounted bars 1
1 bar base-mounted 0.95
several base-mounted bars 0.75



(4) Bus bar Installation Media De rating Factor (K4)
Bus bar Installation Media is Non-ventilated ducting so following Table
De rating Factor is 0.8

Bus Bar Installation Media(K4): De rating Factor
Calm indoor atmosphere 1
Calm outdoor atmosphere 1.2
Non-ventilated ducting 0.8



(5) Bus bar Artificial Ventilation De rating Factor (K5)
Bus bar Installation Media is Non-ventilated ducting so following Table
De rating Factor is 0.9

Bus Bar Artificial Ventilation Scheme (K5): De rating Factor
without artificial ventilation 0.9
with artificial ventilation 1



(6) Enclosure & Ventilation De rating Factor (K6)
Bus bar Area per Phase = Bus width X Bus Thickness X Length of Bus X No of Bus bar per Phase
Bus bar Area per Phase = 75x10xX500X2= 750000mm
Total Bus bar Area for Enclosure= No of Circuit X( No of Phase + Neutral )X Bus bar Area per Phase
Here we used Size of Neutral Bus is equal to Size of Phase Bus
Total Bus bar Area for Enclosure=3X(3+1)X750000mm
Total Bus bar Area for Enclosure=9000000 Sq.mm
Total Enclosure Area= width X Height X Length
Total Enclosure Area=1200x600x2400=1728000000 Sq.mm
Total Bus bar Area for Enclosure / Total Enclosure Area =9000000/1728000000
Total Bus bar Area for Enclosure / Total Enclosure Area=0.53%
Bus bar Artificial Ventilation Scheme is without artificial ventilation so following Table
De rating Factor is 0.95

Volume of Enclosure & Ventilation De rating Factor (K6)
cross Section area of Bus bar/Total Bus Bar Area Indoors ( Panel is well Ventilated) Indoors ( Panel is Poorly Ventilated) Outdoor
0% 0.95 0.85 0.65
1% 0.95 0.85 0.65
5% 0.9 0.7 0.6
10% 0.85 0.65 0.5



(7) Proxy Effect De rating Factor (K7)
Bus bar Phase Spacing (p) is 400mm.
Bus bar Width (e) is 75mm and Space between each bus of Phase is 75mm so
Total Bus length of Phase with spacing (w) =75+75+75+75+75=225mm
Bus bar Phase Spacing (p) / Total Bus length of Phase with spacing (w) = 400 / 225 =2
From following Table De rating factor is 0.82

Proxy Effect (K7): De rating Factor
1 0.82
2 0.82
3 0.82
4 0.89
5 0.95
6 0.99
7 1



(8) Altitude of Bus Bar installation De rating Factor (K8)
Altitude of Panel Installation on Site is 2000 meter so following Table
De rating Factor is 0.88

Altitude of installation site (Meter) (K8) De rating Factor
2200 0.88
2400 0.87
2500 0.86
2700 0.85
2900 0.84
3000 0.83
3300 0.82
3500 0.81
4000 0.78
4500 0.76
5000 0.74

Total De rating Factor= K1XK2XK3Xk4Xk5Xk6Xk7Xk8
Total De rating Factor =1.83x1x1x0.8×0.9×0.95×0.82×0.88
Total De rating Factor =0.90

(2) Bus bar Size Calculation:

Desire Current Rating of Bus bar (I2) =630 Amp
Current Rating of Bus bar after De rating Factor (I1)= I2 X De rating Factor or I2 / De rating Factor
Current Rating of Bus bar after De rating Factor (I1)=630×0.9
Current Rating of Bus bar after De rating Factor (I1)=697Amp
Bus bar Cross Section Area as per Current= Current Rating of Bus bar / Current Density of Material
Bus bar Cross Section Area as per Current= 697 / 1.6
Bus bar Cross Section Area as per Current= 436 Sq.mm
Bus bar Cross Section Area as per Short Circuit= Isc X√ ((K/( θtx100)x(1+ α20xθ) xt
Bus bar Cross Section Area as per Short Circuit= 50000X√ ((1.166/( 100×100)x(1+ 0.00403×85) x1
Bus bar Cross Section Area as per Short Circuit=626 Sq.mm
Select Higher Size for Bus bar Cross section area between 436 Sq.mm and 626 Sq.mm
Final Calculated Bus Bar Cross Section Area =626 Sq.mm
Actual Selected Bus bar size is 75×10=750 Sq.mm
We have select 2 No’s of Bus bar per Phase hence.
Actual Bus bar cross section Area per Phase =750×2= 1500 Sq.mm
Actual Cross Section Area of Bus bar =1500 Sq.mm
Actual Bus bar Size is Less than calculated Bus bar size.

(3) Forces generated on Bus Bar due to Short Circuit Current

Peak electro-magnetic forces between phase conductors (F1) = 2X(l/d)X(2.5xIsc)2/100000000
Total width of Bus bar per Phase(w)=75+75+75=225mm =2.25cm
Bus bar Phase to Phase Distance (d)=400+225=625mm=6.25cm
Peak electro-magnetic forces between phase conductors (F1) =2x(50/63)x(2.5×50000)2/100000000
Peak electro-magnetic forces between phase conductors (F1)=250 Kg /cm2
Peak electro-magnetic forces between phase conductors (F1)=2.5 Kg /mm2
Actual Forces at the head of the Supports or Bus Bar (F)=F1X(H+h/H)
Actual Forces at the head of the Supports or Bus Bar (F)=2.5x(100+5/100)
Actual Forces at the head of the Supports or Bus Bar (F)= 3 Kg /mm2
Permissible Strength of Insulator (F’) is 10 Kg/mm2
Actual Forces at the head of the Supports or Bus Bar is less than Permissible Strength
Forces on Insulation is in within Limits

(4) Mechanical strength of the bus bars

Mechanical strength of the bus bars=(F1X i /12)x(1/ Modulus of inertia of a bus bar )

Value of Modulus of inertia of a bus bar or of a set of bus bars (i/v)
No of Bus Strip per Phase Vertical Bus Bar (cm3) Horizontal Bus Bar (cm3)
1 1.66 16.66
2 14.45 33.33
3 33 50



From above table Value of Modulus of inertia of a bus bar=14.45
Mechanical strength of the bus bars=(250×50/12)X(1/14.45)
Mechanical strength of the bus bars= 72 Kg/cm2
Mechanical strength of the bus bars= 0.72 Kg/mm2
Permissible Bus bar Strength is 12 Kg/mm2
Actual Mechanical Strength is less than Permissible Strength
Mechanical strength of Bus bar is in within Limit

(5) Temperature Rise Calculation

Specified Maximum Temperature Rise (T1) is 35°c
Calculated Maximum Temperature Rise (T2)=T/(log(I1/I2)1.64)
Calculated Maximum Temperature Rise (T2)=35/(Log(697/630)1.64)
Calculated Maximum Temperature Rise (T2)= 30°c
Calculated Bus bar Temperature rise is less than Specified Max Temperature rise
Temperature Rise is in within Limit

Results:

Size of Bus bar = 2No’s 75x10mm per Phase.
Total No of Feeder =3 No’s
Total No’s of Bus bar = 6 No’s 75x10mm for Phase and 1No’s 75x10mm for Neutral.
Forces at the head of the Supports or Bus Bar (F)= 3kg/mm2
Mechanical strength of the bus bars= 0.7 Kg/mm2
Maximum Temperature Rise=30°c

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