Enclosure correction factor (k2) ratio of total conductor bus bar crosssection 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. 5.
6.
Correction factor (k3) for busbar material = 1 Up-rating factor (k4) for PVC Sleeving bus bar = 1
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 θ
f I
A T Isc
=Final conductor temp after the fault = 160°C. = Initial conductor temp before the fault = 75°C. = Cross sectional area of conductor (Sq. inch) =? = Duration of fault (sec.) = 1 Sec. = Short circuit current = 50KA. A
Isc x T ---------------------------------------------θ f + 258
Or
A=
14 x 10
log10 ---------------θ
50,000 x Or
A=
A=
1
---------------------------------------------- = 0.93 in 160 + 258
14 x 10
Or
I + 258
600 mm
.
log10 ---------------75 + 258
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 CONDUCTORS: -
RISE
CALCULATION
OF
Max. Temperature at full Load condition: i.e. When 3200Amp. Flows thru steady state temperature of 45 C.
Full Load Current T max = Ambient X ------------------------------------------------------- X Allow Trise Actual Current Rating of used Conductors 45 + (3200 / 3291) [45+40].
x 40 = 82.8
C which is within the limit of 85 C
Summary: Hence the designed bus bar for Main Panel is OK & within the safe limit. Reference:
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.
1.0 2.0 3.0
Used Current Rating in Amp. 1600Amp . 800Amp. 630Amp.
Used Bus Bar Size:
2x100x10 – For Ph. 1x100x10 – For N. 100x10 – For Ph. 100x6 – For N. 80x10 – For Ph. 80x6 – For N.
Current Rating as per INDALHand Book Table No. 8.4 in Amp.
