Panel Arrangement

BUS BARS AND TERMINALS

Following factors must be considered while selecting the busbars

Permissible temperatures of bus bar and equipments at rated currents and at short circuit conditions.

Max.temperature for bus bar joints permissible as per DIN 43673 is 120°C

Permissible temperature rise for external connection as per IEC 694-1 is 60°C for Cu and 70°C for Silver plated terminal.

Permissible temperature rise limits of equipments in the vicinity

Permissible temperature rise limits of insulating materials

Power loss =Heat loss due to convection + Heat loss due to radiation. I²R = 2.74(T-T0)1.25 X h+b/ h1/4 XL+ 5.669 X 10-8 X 2(h+b) Є (T4 – T0

4) XL

R- Resistance at TºC = R40(1+ aXΔTºC),T 0 = Ambient temp in K(273 +40)T = End temperature of bus bar in K(273 + T°C) R35= ς L/aς= receptivity of conducting material (0.0265 for Al,0.0178 for Cu)a.= coefficient of resistively (0.0043 for Al, 0.00393 for Cu)Є= emissivity (0.216 for Al,0.0921 for Cu) L = length of bus bar(in m)h = width of bus bar (in m)b= Thickness of bus bar (in m)

Note:- The calculated value of current is in open air, actual value will be less as the heat loss is not higher in the enclosed panel.Actual capacity is to be checked on a sample panel to know the correction factor to be applied for the particular design of panel.

The current carrying capacity of bus bars can be calculated by equating the power loss in the busbar by the current to the heat loss due to convection and radiation.

Temperature rise limits as per IEC 947

Current carrying capacity for Al bus bars can be determined from DIN 43670Ambient of 35°C and operating temperature of 65°C

Current carrying capacity for Cu bus bars can be determined from DIN 43671Ambient 35°C and operating temperature of 65°C

Correction factor k1 for lesser conductivity of Al

Correction factor k2 for different ambient temperature,

Ambient

Correction factor k3 for horizontal mounting

Correction factor k4 for distance between phases

Correction factor k5 for operating 1000m above see level