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Calculation for Short Circuit Current Calculation using IEC / IEEE Standard. This report contains the description for calculating the short circuit current using IEEE 909 and circuit breaker…Full description
SCDeskripsi lengkap
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
(1)
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
THERMAL RATING a)
Rating as per Table 2 (INDAL) For 3 x 200 mm x 12 mm Aluminium Bus Bars
b)
Derating Factor
c)
5300 Amps
•
Temperature Rise of 35OC over an ambient of 50OC.
0.817
•
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
Actual Current Rating of above Bus Bars
Conclusion
0.80 x 5300 4240 Amps
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
=
85 C
Q2 =
Final Temperature
=
200OC
A
Cross Sectional Area in Sq. inch
=
A =
Ix
O
t
14 x 10
4
Q2 + 258 log 10 Q1 + 258
X)
O
Cross sectional Area in case of initial temperature of 85 C and final temperature of 200OC.
=
3
65 x 10 x 14 x 10
1
4
458 log 10 343 = =
1.309 Sq. inch 845 Sq.mm
Conclusion
(3)
Area considered is 7200 Sq.mm – Hence SAFE
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
xK 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 =
6
16 x 65 x 70 x 10 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.
(4)
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.