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BUS DUCT DESIGN CALCULATION FOR 1000KVA TRANSFORMER

Capacity of transformer1000KVA (2000A Busses)Nominal voltage- 415 voltsSystem frequency50 HzShort circuit current28000ALocationIndoor well ventilated

Ambient temperature - 35Permissible temperature rise on steady state thermal condition -40Permissible temperature rise on short circuit condition - 100Initial temperature to be taken for short circuit condition-70Duration of fault -1 secMaterial for busesAluminium Alloy INDAL D50S WP

Allowable tensile stress on aluminium bus bar -1025 Kg/Youngs modules of aluminium-E =0.67 x Kg/Temperature coefficient of resistance 20 degree Celsius for aluminium- 0.00363Support for busesSMC

Allowable shear stress on SMC -55.5 Kg/Suggested size:

Bus size2 runs 127 x 10 mm for phase and 1 run 127 x 10 mm for neutralEnclosure size800 x 500 mm

Center to center distance between buses150 mmClearance between buses and enclosure100 mmSize of SMC support80mm width and 20mm thickness

Number of supports at a location2 No (one at top and other at bottom)Spacing between support500 mm

a)Steady state thermal condition :

Current rating of 2 runs of 127 x 10 mm buses of INDAL D50S WP to 50- 2930ADerating factor due to ambient temperature0.945Derating factor for Grade of Aluminium1.000Derating factor due to size of Enclosure -0.775

Derating factor due to proximity Effect1.000Derating factor due to frequency variation1.000Overall Derating factor=0.732

Conductor area = 127 x 10 x 8 =10160 Enclosure area = 800 x 500 =400000Conductor area in percentage =3%Actual current rating of proposed buses = 2930 x 0.732= 2144.76AConclusion:-Safe as the rating work out to be 2144.76 Amps as against 2000 Amps required.

b) Short circuit condition

Temperature rise in degree Celsius of conductor for one sec fault duration

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Permissible temperature rise is 100The minimum area of cross section of conductor shall be

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For fault level of 50 KA for 1 secThe minimum cross sectional area will be = 50/0.08269

=604.67 sq mm

Proposed buses have more sectional area.So adequate

c) Stress on busbars:

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