01.03.2007 (Rev.)

CALCULATIONS IN SUPPORT OF FAULT LEVEL OF 65 kA FOR ONE SECOND

4000 A TP ALUMINIUM BUS DUCT

DRAWING NO.G 7643 R0

i) Rating 4000 Amps ii) Bus Bars Per Phase 3 x 200 mm x 12 mm iii) Fault Level 65 kA for 1 Second iv) Enclosure In a ventilated room v) Ambient Temperature 50OC vi) Working Temperature 85OC vii) Rating Chart INDAL Electrical Grade Aluminium

(1) THERMAL RATING

a) Rating as per Table 2 (INDAL) 5300 Amps For 3 x 200 mm x 12 mm Aluminium Bus Bars

b) Derating Factor

• Temperature Rise of 35OC 0.817 over an ambient of 50OC. • Magnetic Enclosure 0.850

• Proximity Factor 1.000

• Enclosure Factor 0.920 • Paint / Sleeving Factor 1.250 • Combined Derating Factor 0.817 x 0.850 x 1.000 x 0.920 x 1.250

0.799 Say 0.80

c) Actual Current Rating of above 0.80 x 5300 Bus Bars 4240 Amps

Conclusion Safe as the rating works out to be 4240 Amps as against 4000 Amps required.

….Contd..2

(2)

(2) SHORT TIME RATING

I Short Circuit Current = 65 kA T Short Circuit Time = 1 Second Q1 Initial Temperature = 85OC Q2 = Final Temperature = 200OC A = Cross Sectional Area in Sq. inch A = I x t

14 x 10 4 Q2 + 258

log 10 Q1 + 258

X) Cross sectional Area in case of initial temperature of 85OC and final temperature of 200OC. = 65 x 103 x 1

14 x 10 4

458 log 10

343 = 1.309 Sq. inch = 845 Sq.mm

Conclusion Area considered is 7200 Sq.mm – Hence SAFE

(3) MECHANICAL STRESS & INSULATOR SPAN FM Mechanical Force Developed at the time of Short Circuit.

I Short Circuit Current.

K Space Factor For Rectangular Bus Bar.

S Spacing between the Phases = 190 mm.

FM = 16 x I 2 x 10 - 4 x K N/M S

….Contd..3

(3)

The value of K as calculated from the graph given in J&P Hand Book page 212 by taking the ratio (S-a) / (a+b) on comparing it with a/b will be 0.50. Hence FM = 16 x 65 x 70 x 10 6 x 10 - 4 x 0.50

190

= 19158 N/M = 1954.88 Kg Per Meter

Force Developed at a span of 350 mm = 1954.88 x 0.350 = 684.20 Kg.

Since there are two supports – one at on top and one at bottom, force per support will be 342.10 Kg.

a) Powermat supports (SMC) type 312-K having capacity to withstand force of

2000 kg will be provided meaning thereby that there will be a safety factor of 5.85 times.

b) Distance : The support to support distance of max 350 mm will be

maintained.

c) Above calculations / recommendations are OK for a phase to phase gap of 130 mm.

(4) FINAL DESIGN OFFERED

Chamber Size 700 mm (minimum) Bus Bars 3 x 200 mm x 12 mm per phase Phase to Phase Gap 130 mm Support to Support Distance 350 mm