The word busbar, derived from the Latin word omnibus ('for all'), gives the idea of a universal system of conveyance. In the electrical sense, the term bus is used to describe a junction of circuit...
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Descripción: GEV de Pullman Bus. Se incluyen 6 partes del plan de un total de 10.
1) ALUMINIUM BUS BAR SIZING CALCULATIONS FOR 4000A Specifications for Busbar 1. Rated currents 2. Rated voltage 3. Ambient temp 4. Final temp 5. Busbar section
: 4000A : 415V AC : 45ºC : 85ºC : 4 Runs X 125 X 10 mm per phase 2 Runs X 125 X 10mm per neutral
6. Material
: Aluminum
Current Carrying Capacity of Conductor (2 Runs x 127mmx 9.53mm) =2930A (As per INDAL & CO, IN TABLE NO.2) Approximation for busbars of 4 Runs x 125mmx 10mm = 6052 A Base on the above following de-rating factors are considered 1. Temperature correction factor for 40° C rise over ambient of 45° C = 0.88 2.
Since the Busbar are enclosed in sheet steel enclosure & the cross sectional area of the aluminum is less than 3% of cross sectional area of Busbar chamber, the above obtained rating is further decreased by a factor = 0.91.
Therefore total current capacity of 4 Runs x 125 X 10 mm Aluminium busbar = 6052A x 0.88 X 0.91
=4846A Which is greater than required rating 4000 A (Considered as 40 deg rise on ambient of 45 deg. C).
2) Temperature Rise Calculations (11 / 12) 1.7= θ1 / θ2 11 = Rated current required = 4000A 12 = Rated current obtained =4846A θ2 = Max. Temp. rise Permissible = 40ºC θ1 = Max. Temp. Rise obtained θ1 = (11 / 12) 1.7 x θ2 = (4000/4846) 1.7 X 40 = 28.86ºC Max Temp. rise obtained=28.86ºC over & above the ambient temperature of 45º C is within the limits
2. EFFECTS OF SHORT CIRCUIT CURRENT FOR ALUMINIUM BUSBARS
FROMJ & P SWITCHGEARHANDBOOK- 7 THEDITION PAGE 207 II
THE MAGNITUDE OF THE CURRENT WHICH FLOWS ON THE OCCURANCE OF A SHORT CIRCUIT CAN BE EXCEEDINGLY HIGH AND EVENTHOUGH IT PERSISTS FOR A VERY SHORT WHILE, IT MUST BE CONSIDRED BOTH IN DERATING THE SECTIONAL AREA OF THE BUSBAR AND CONDUCT TO MATERIAL AND IN THE DESIGN OF SUPPORTING STRUCTURES. 2.1 THE FIRST OF THESE PROBLEM IN THERMAL IN THAT THE CONDUCTOR TEMPERATURE MAY RISE, IF THE SECTIONAL AREA IS INADEQUATE, TO A DANGEROUS LEVEL. IT HAS TO BE NOTED THAT THIS IS DIRECTLY RELATED TO THE R.M.S. VALUE OF THE FAULT CURRENT AND THE TIME IT HAS TO BE CARRIED. THREFORE, TO DETERMINE THE SECTIONAL AREA OF THE CONDUCTORS TO CARRY THE ASSIGNED FAULT CURRENT FOR THE CONDUCTORS THEMSELVES, BUT ALSO FOR ANY INSULATION WHICH MAY BE IN CONTACT OR NEAR THE CONDUCTORS AND FORMULA FOR CALCULATING THE TEMPERATURE RISE IN DEG.
FROM CURVES PRODUCED BY ALCAN INDUSTRIES LTD. REPRODUCED IN J&P SWITCHGEAR BOOK IN PAGE NO.209 THE VALUE IA X √t CANBE DEDUCTED
DIRECTLY FOR A KNOWN INITIAL TEMPERATURE AND A DESIRED FINAL TEMPERATURE. THE CURVES ARE BASED ON THE FORMULA.
For fault level of 50kA for 1 sec The minimum cross sectional area will be =50/ 0.775 =645 sq mm Hence for 50kA, But We have considered 5000sq mm, which is a safe design.
Also for 65kA A= 65/ 0.0775 A= 838.7 sq mm But we have considered 5000Sq mm, which is safe design for 65kA fault.
