VEE VEE CONTROLS PVT. LTD.
Bangalore
DESIGN CALCULATIONS
FOR
THERMAL WITHSTAND CAPABLITY, TEMPERATURE RISE &
SHORT CIRCUIT RATING
11kV, 26.3kA FOR 3 Sec, 800A, COPPER BUSBAR
Prepared By Checked By Approved By
D.R.JAYARAM
Page 1 of 4
VEE VEE CONTROLS PVT. LTD. Bangalore
Design parameters
1 Rated Voltage - 11kV
2 Frequency - 50Hz
3 Rated Current - 800A
4 Enclosure Material - CRCA
5 Busbar Material - Copper (EC-Grade)
6 Busbar Size - 1Rx80x10mm Flat.
7 Cross Sectional Area of the busbar - 800 Sq. mm
8 Short Circuit Current (Isc) - 26.3 kA.
9 Duration of Short Circuit (T) - 3 Sec.
10 Altitude - less than 1000Mts
11 Design Ambient Temperature - 500 C
12 Temperature rise over specified ambient temp. - 350 C
13 Hot spot temperature of Conductor Carrying Rated Current - 850 C
14 Hot spot temperature of Enclosure - 700 C
15 Max. Temperature Rise of Conductor during fault condition
While carrying rated current - 2000 C Over design ambient temperature
Page 2 of 4
VEE VEE CONTROLS PVT. LTD. Bangalore
Thermal Withstand Capability
Continues Current Rating
LASCPT PANEL
50°C = Designed Ambient Temperature
85°C = Final Temperature.
Required current as per specification = 800A.
Bus bar size = 1Rx80x10mm Copper
Current carrying capacity of Copper bus bar after correction due to various factors
Correction factor- K= K1xK2xK3xK4xK5
Continuous current carrying capacity of 1Rx80x10mm Cu. Bus bar as per DIN 43671 for initial
ambient temperature of 50°C & Conductor temperature of 85°C = 1500A
K1:- Conductivity factor = 1.0 (for Copper Busbar load variations relating to conductivity is
56m/Ωmm2) (
K2:- Correction factor for initial temperature of 50°C and final temperature of 85° C = 1.05
K3:- Correction factor bus bar more than 2mtr. = 0.80 (considered minimum factor for 2 nos.)
K4:- Correction factor for bus bar layout = 1.0 (K4 is applicable for bubsar more than 1 run/phase,
we have consider deration factor 1 because we have used 1 run bus bar in Panel.
K5:- Correction factor for influence specific to location = 0.99 (reduction in load at altitude below
2000mts, height above sea level)
Correction factor- K= K1xK2xK3xK4xK5
Correction factor K= 1.0x1.05x0.8x1.0x0.99= 0.8316
Corrected current rating = K x 1500 = 0.8316x 1500= 1,247.4A
Current rating required = 800A.
Current rating arrived after considering correction factors = 1,247.4A
Conclusion: The bus bar 1Rx80x10mm carries current rating of 1247.4A. Which is more than the
requirement of 800A
Temperature Rise Calculation for Continuous Current Rating
Current Rating ( Ir ) = 800A
Continuous Current Rating of the Busbar ( Ic ) = 1247.4A
Final Temperature ( Tf) = 85ºC
Ambient Temperature (Ta ) = 50 ºC
Rise in Temperature ( Tr ) = ( Tf-Ta) = 35 ºC
Estimated = 35( Ir/Ic) ^1.7
35(800/1247.4) ^1.7
16.44 ºC
Page 3 of 4
VEE VEE CONTROLS PVT. LTD. Bangalore
Calculation of Short Circuit Rating:
Minimum Cross section required to rise the Temperature of conductor from 85 0 C to 2000 C is
calculated using the formula (Refer Annex A.3):
Icu
A = ------------------------------------------------------
0.22 x 104 x log 2 -20 + (25400/G)
t 1 + 20 + (25400/G)
Where
Icu = Maximum rms amperes for copper conductor- 26300 A
A = cross-sectional area in square inches - -- sqin
t = the duration of the constant current flow - 3 Sec.
1 = Operating Temperature - 850 C
2 = Max. Temperature allowed on SC - 2000 C (Min.)
(Note: Max. Allowed is 3000 C)
G = the conductivity in percent IACS - 95% (Min.)
26300
A = ------------------------------------------------------
0.22 x 106 x log -20 + (25400/95)
3 + 20 + (25400/95)
26300
A = ------------------------------------------------------
0.22 x 106 x log
3
A = 0.727522083 Sq.in
Minimum Area of conductor required = 0.7334745 Sq.in
Minimum Area of conductor required in mm = 0.7334745 * 645.16 Sq.mm
= 473.2 Sq.mm
The Cross section area actually adopted = 800 Sq. mm
Page 4 of 4
