Electrical -Bus Bar Sizing
9
Bus Bar Calculation for Main LT Panel A. Bus Bar size calculation for 3200A Rating Panel: - CONDITIONS Rating Current: 3200Amp. System: 415Vac, TPN, 50Hz. Fault Level: 50KA. For 1 Sec. Operation Temp: 40°C rise over 45°C ambient. CONSIDERATION Enclosure size: 1400mm. wide X 400mm. height Bus bar Size: 2:200x10 per Ph., 1:200x10 for Neutral. Bus bar material: Electrolytic gr. Al. (IS 63401/AA6101) CALCULATION 1. AC Current rating for Dual Al. Flats 200x10mm considered = 4750Amp. (As per Table – 8.4 as INDAL hand book) 2. Ambient correction factor (k1) 45°C rise over 35°C (ambient) = .88 (As per Table – 5 as INDAL hand book) If ambient Temp. 45°C instead of 35°C than De-rating Factor = 1-θ° C x α
description
Electrical -Bus Bar Sizing
Transcript of Electrical -Bus Bar Sizing
Bus Bar Calculation for Main LT Panel
A. Bus Bar size calculation for 3200A Rating Panel: -
CONDITIONS
Rating Current: 3200Amp.
System: 415Vac, TPN, 50Hz.
Fault Level: 50KA. For 1 Sec.
Operation Temp: 40°C rise over 45°C ambient.
CONSIDERATION
Enclosure size: 1400mm. wide X 400mm. height
Bus bar Size: 2:200x10 per Ph., 1:200x10 for Neutral.
Bus bar material: Electrolytic gr. Al. (IS 63401/AA6101)
CALCULATION
1. AC Current rating for Dual Al. Flats 200x10mm considered = 4750Amp.
(As per Table – 8.4 as INDAL hand
book)
2. Ambient correction factor (k1) 45°C rise over 35°C (ambient) = .88
(As per Table – 5 as INDAL hand book)
If ambient Temp. 45°C instead of 35°C than De-rating Factor = 1-θ° C x α
θ = Temp difference = 45°C - 35°C = 10
α = Resistance-Temp. Coefficient for Al. Bus= 0.00403
k1A = 1-10 x 0.00403 = 0.96
3. Enclosure correction factor (k2) ratio of total conductor bus bar cross-
section to enclosure cross-section.
(3 x 2 x 200 x 10) x 100
--------------------------------- = 2%
1400 x 400
De-rating factor for enclosure = 0.82
(As per Table – 5 as INDAL hand book)
4. Correction factor (k3) for busbar material = 1
5. Up-rating factor (k4) for PVC Sleeving bus bar = 1
6. Total Combined De-Rating factor = k1xK1Axk2xk3xk4
= 0.88 x 0.96 x 0.82 x 1 x 1
= 0.693
So, actual rating of considered busbar = 4750 x 0.693 = 3291Amp.
Conclusion: -
It means 2:200x10mm Al. Bus Bar is much sufficient for
3200A Rating as per actual operating conditions.
B. Minimum Conductor size for Stand 50KA Fault : -
While considering short circuit condition, assuming a steady state average
temperature of 75°C and final temperature of 160°C then required bus
section:
CALCULATION: (As per table – 17)
Let θ f =Final conductor temp after the fault = 160°C.
θ I = Initial conductor temp before the fault = 75°C.
A = Cross sectional area of conductor (Sq. inch) =?
T = Duration of fault (sec.) = 1 Sec.
Isc = Short circuit current = 50KA.
A θ f + 258
Or Isc = 14 x 10 ------ log10 ----------------
T θ I + 258
Isc x T
Or A = ----------------------------------------------
θ f + 258
14 x 10 log10 ----------------
θ I + 258
50,000 x 1
Or A = ---------------------------------------------- = 0.93 in
160 + 258
14 x 10 log10 ----------------
75 + 258
Or A = 600 mm. Considered bus section = 2x200x10 = 4000mm.
Conclusion: -
It means 2:200x10mm Al. Bus Bar is much sufficient for
stand 50KA Fault Current for 1Sec.
C. TEMPERATURE RISE CALCULATION OF
CONDUCTORS : -
Max. Temperature at full Load condition: -
i.e. When 3200Amp. Flows thru steady state temperature of 45C.
Full Load Current
T max = Ambient X ------------------------------------------------------- X Allow T rise
Actual Current Rating of used Conductors
45 + (3200 / 3291) x 40 = 82.8C which is within the limit of 85C
[45+40].
Summary: Hence the designed bus bar for Main Panel
is OK & within the safe limit.
Reference: INDAL hand book
And IS: 8623 (Part – 1) of 1993.
Bus Bar Calculation for Bus Duct
A. Bus Bar size calculation for 3200A Rating Bus
Duct: -
CONDITIONS
Rating Current: 3200Amp.
System: 415Vac, TPN, 50Hz.
Fault Level: 50KA. For 1 Sec.
Operation Temp: 40°C rise over 45°C ambient.
CONSIDERATION
Enclosure size: 750mm. wide X 450mm. height
Bus bar Size: 2:200x10 per Ph., 1:200x10 for Neutral.
Bus bar material: Electrolytic gr. Al. (IS 63401/AA6101)
CALCULATION
1. AC Current rating for Dual Al. Flats 200x10mm considered = 4750Amp.
(As per Table – 8.4 as INDAL hand book)
2. Ambient correction factor (k1) 45°C rise over 35°C (ambient) = .88
(As per Table – 5 as INDAL hand book)
If ambient Temp. 45°C instead of 35°C than De-rating Factor = 1-θ° C x α
θ = Temp difference = 45°C - 35°C = 10
α = Resistance-Temp. Coefficient for Al. Bus= 0.00403
k1A = 1-10 x 0.00403 = 0.96
3. Enclosure correction factor (k2) ratio of total conductor bus bar cross-
section to enclosure cross-section.
(3 x 2 x 200 x 10) x 100
--------------------------------- = 3.5%
750 x 450
De-rating factor for enclosure = 0.78
(As per Table – 5 as INDAL hand book)
4. Correction factor (k3) for bus bar material = 1
5. Up-rating factor (k4) for Black Matt Painted bus bar = 1.2
6. Total Combined De-Rating factor = k1xK1Axk2xk3xk4
= 0.88 x 0.96 x 0.78 x 1 x 1.2
= 0.79
So, actual rating of considered bus bar = 4750 x 0.79 = 3752Amp.
Conclusion: -
It means 2:200x10mm Al. Bus Bar is much sufficient for
3200A Rating as per actual operating conditions.
Summary: Hence the designed bus bar for Bus Duct is
OK & within the safe limit.
Reference: INDAL hand book
And IS: 8623 (Part – 1) of 1993.
Bus Bar Calculation for Other Panels [Main Bus]
Sl.
No.
Used
Current
Rating in
Amp.
Used Bus Bar Size:
Current Rating
as per INDAL-
Hand Book
Table No. 8.4
in Amp.
Max.
[Approx]
Total De-
Rating
Factor
Actual
Current
Rating
1.0 1600Amp
.
2x100x10 – For
Ph.
1x100x10 – For N.
2650Amp. 0.7 1855Amp
2.0
800Amp.
100x10 – For Ph.
100x6 – For N.
1565Amp. 0.7 1095Amp
3.0
630Amp.
80x10 – For Ph.
80x6 – For N.
1250Amp. 0.7 875Amp
