Sunday, November 22, 2009
Wednesday, November 11, 2009
b) Step 2
b) Step 2 Calculation of Short ckt forces & short ckt stress.
Calculate Peak electro-magnetic forces between phase conductors
Calculate Peak electro-magnetic forces between sub conductors
Calculate Peak electro-magnetic forces between phase conductors
Calculate Peak electro-magnetic forces between sub conductors
20)Step 1
a) Step 1
Collect the system data for which busbar system has to be design
VOLTAGE RATING 415V, 50Hz. 3Ph. - 3Wire
CURRENT RATING 2000Amp.
WELL VENTILATED ROOM
MAX. FAULT CURRENT 50 KA
LENGTH OF BUSBAR = 500mm
AVERAGE AMBIENT TEMP. = 50 deg. Centigrade
Calculate the derating factors for ambient temperature, enclosure, proximity effect.
1) Derating factor for Ambient Temperature
Df1=0.81
Actual average ambient temp. = 50 deg. C
Manufacturer average ambient temp. = 35 deg. C
Final ambient temp. = 85 deg. C
2) Derating factor for enclosure & ventilation
From table we can see that for well ventilated room, where cross-sectional area of busbar is 10% of total cross-sectional area of enclosure derating factor is
Df2=0.65
3) Derating factor for Proximity effect
For 3W phase spacing derating factor for proximity effect is
Df3=0.82
Calculate effective derating factor.
Df = 0.81 * 0.65 * 0.82
= 0.43
Select the busbar size
Minimum rating of busbar required
= 2000/0.43
= 4651 amp.
Busbar selected = 203.2 * 9.53 mm (3 flats)
Collect the system data for which busbar system has to be design
VOLTAGE RATING 415V, 50Hz. 3Ph. - 3Wire
CURRENT RATING 2000Amp.
WELL VENTILATED ROOM
MAX. FAULT CURRENT 50 KA
LENGTH OF BUSBAR = 500mm
AVERAGE AMBIENT TEMP. = 50 deg. Centigrade
Calculate the derating factors for ambient temperature, enclosure, proximity effect.
1) Derating factor for Ambient Temperature
Df1=0.81
Actual average ambient temp. = 50 deg. C
Manufacturer average ambient temp. = 35 deg. C
Final ambient temp. = 85 deg. C
2) Derating factor for enclosure & ventilation
From table we can see that for well ventilated room, where cross-sectional area of busbar is 10% of total cross-sectional area of enclosure derating factor is
Df2=0.65
3) Derating factor for Proximity effect
For 3W phase spacing derating factor for proximity effect is
Df3=0.82
Calculate effective derating factor.
Df = 0.81 * 0.65 * 0.82
= 0.43
Select the busbar size
Minimum rating of busbar required
= 2000/0.43
= 4651 amp.
Busbar selected = 203.2 * 9.53 mm (3 flats)
19) Calculation Example
19) Calculation Example
Up till now we have seen all the theoretical part of bus bar design & all the formulae which are required for calculating short ckt forces & stress.
Now will take one practical example for busbar calculation for better understanding.
The example is divided in three steps
Step 1) In this we are going to collect the system data for which busbar system is to be designed & then calculate derating factors for ambient temperature, ventilation& proximity effect. Then we will calculate effective derating factor & calculate the busbar size.
Step 2) After selecting the busbar calculate the value of “as” this is used to calculate peak electromagnetic short ckt forces between phase & between sub conductors. Then calculate peak electromagnetic short ckt forces between phase & between sub conductors. Then calculate total stress on busbar.
Step3) Adjustment should be carried out to maintain the stress within limit of busbar; accordingly busbar support must be selected.
Up till now we have seen all the theoretical part of bus bar design & all the formulae which are required for calculating short ckt forces & stress.
Now will take one practical example for busbar calculation for better understanding.
The example is divided in three steps
Step 1) In this we are going to collect the system data for which busbar system is to be designed & then calculate derating factors for ambient temperature, ventilation& proximity effect. Then we will calculate effective derating factor & calculate the busbar size.
Step 2) After selecting the busbar calculate the value of “as” this is used to calculate peak electromagnetic short ckt forces between phase & between sub conductors. Then calculate peak electromagnetic short ckt forces between phase & between sub conductors. Then calculate total stress on busbar.
Step3) Adjustment should be carried out to maintain the stress within limit of busbar; accordingly busbar support must be selected.
10)Stiffeners
Stiffeners
Formula for Design of insulating supports
Area of SMC reqd. = Peak force × Safety factor /Strength of SMC
...............
Formula for Design of insulating supports
Area of SMC reqd. = Peak force × Safety factor /Strength of SMC
...............
9)Calculation stresses created by short circuit force
1) Stresses because of s/c forces between Phase conductors
Where, z = section modulus
= 0.167*d2* b for horizontal orientation
=0.167 n* d* b2 for vertical orientation
2) Stresses because of s/c forces between sub-conductors
Where, zs =0.167d2 b
Total stress on busbar conductors
TOTAL = Stresses because of s/c forces between Phase conductors + Stresses because of s/c forces between sub-conductors
Where, z = section modulus
= 0.167*d2* b for horizontal orientation
=0.167 n* d* b2 for vertical orientation
2) Stresses because of s/c forces between sub-conductors
Where, zs =0.167d2 b
Total stress on busbar conductors
TOTAL = Stresses because of s/c forces between Phase conductors + Stresses because of s/c forces between sub-conductors
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