ArcEnergy
Electrical
- Aug 25, 2015
- 8
Hello all.
I have posted this question in Thermodynamics forum and I am posting here again to get some opinions by electrical engineers who might have experience with similar situation as mine.
My question is to estimate the amount of temperature rise inside the enclosure due to solar loading. I am writing in two Parts. the PART 1 is what I am trying to achieve and PART2 is what I have already calculated.
PART 1:
I have a Switchgear enclosure (made of aluminum) of LxWxH of 2.4mx1.15mx1.97m , Thickness would be around 0.01m
The internal power Dissipation is 900W .. it is because of a current of 12.5kA flowing in a conductor of resistance 6x10^-6 Ohms
The ambient temperature (Tamb) is 40°C
I am considering the Solar Radiation of 1100W/m^2. The enclosure is painted with light Grey color with Absorption coefficient of 0.5 and emittance coeff of 0.87 (correct me if I am wrong)
h for the Aluminum as 2 W/m^2K (not sure if this value make sense)
I would like to know how much would be the temperature rise inside the enclosure (Tenc).
PART 2:
I have done the calculations based on just current and temperature rise values as explained below
The switchgear is tested with 12.5kA of rated current at 40°C of ambient temperature. according to standards we are allowed to have a 65K of rise inside the switchgear cubicle. this value is mainly because the current carrying conductor has only tested to withstand 105°C. as you see the allowed temperature rise is 105°C-40°C = 65K
I have then calculated the effect of different ambient temperatures on conductor current by keeping the conductor temperature of 105°C constant using the formula
Inew/Irated = sqrt[(105°C - Tamb new)/Temp rise allowed]
Eg: If the Tamb new is 50°C, then Inew = Irated x sqrt [55/65) gives us the new Current of 11.5kA .. That means when the out side temp is 50°, I am only allowed to pass 11.5kA in the conductor.
Now considering the situation of placing the switchgear in outdoors. The additional effect is solar radiation. According to the standard "C37.24-2003 - IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-Enclosed Switchgear"
for grey painted enclosures, the absorption is 0.50 which increases a temperature rise of 7.7K when the solar radiation is 1044 W/m2... So in my new calculation, I have added this 7.7K to my allowed 65K temp rise and calculated the Inew for the amb temp of 40°C. I get the value of 11.64 as allowed current in the conductor when placed my switchgear in outdoors at 40°C.
I don't know if my above calculations make sense because they didn't consider the enclosure dimensions or heat convection and radiation etc.
Can someone tell me if the calculations based on IEEE standard are trustable.. If yes then why? or is there any other way to estimate the temperature rise considering the all the parameters that I mentioned in the first part.
Thanks in advance
regrads,
ArcEnergy
I have posted this question in Thermodynamics forum and I am posting here again to get some opinions by electrical engineers who might have experience with similar situation as mine.
My question is to estimate the amount of temperature rise inside the enclosure due to solar loading. I am writing in two Parts. the PART 1 is what I am trying to achieve and PART2 is what I have already calculated.
PART 1:
I have a Switchgear enclosure (made of aluminum) of LxWxH of 2.4mx1.15mx1.97m , Thickness would be around 0.01m
The internal power Dissipation is 900W .. it is because of a current of 12.5kA flowing in a conductor of resistance 6x10^-6 Ohms
The ambient temperature (Tamb) is 40°C
I am considering the Solar Radiation of 1100W/m^2. The enclosure is painted with light Grey color with Absorption coefficient of 0.5 and emittance coeff of 0.87 (correct me if I am wrong)
h for the Aluminum as 2 W/m^2K (not sure if this value make sense)
I would like to know how much would be the temperature rise inside the enclosure (Tenc).
PART 2:
I have done the calculations based on just current and temperature rise values as explained below
The switchgear is tested with 12.5kA of rated current at 40°C of ambient temperature. according to standards we are allowed to have a 65K of rise inside the switchgear cubicle. this value is mainly because the current carrying conductor has only tested to withstand 105°C. as you see the allowed temperature rise is 105°C-40°C = 65K
I have then calculated the effect of different ambient temperatures on conductor current by keeping the conductor temperature of 105°C constant using the formula
Inew/Irated = sqrt[(105°C - Tamb new)/Temp rise allowed]
Eg: If the Tamb new is 50°C, then Inew = Irated x sqrt [55/65) gives us the new Current of 11.5kA .. That means when the out side temp is 50°, I am only allowed to pass 11.5kA in the conductor.
Now considering the situation of placing the switchgear in outdoors. The additional effect is solar radiation. According to the standard "C37.24-2003 - IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-Enclosed Switchgear"
for grey painted enclosures, the absorption is 0.50 which increases a temperature rise of 7.7K when the solar radiation is 1044 W/m2... So in my new calculation, I have added this 7.7K to my allowed 65K temp rise and calculated the Inew for the amb temp of 40°C. I get the value of 11.64 as allowed current in the conductor when placed my switchgear in outdoors at 40°C.
I don't know if my above calculations make sense because they didn't consider the enclosure dimensions or heat convection and radiation etc.
Can someone tell me if the calculations based on IEEE standard are trustable.. If yes then why? or is there any other way to estimate the temperature rise considering the all the parameters that I mentioned in the first part.
Thanks in advance
regrads,
ArcEnergy