Assume PF of transformer is .8.
rating of transformer=1500kVA=1500X.8=1200kW
V=433(3phase)
So that maximum current-
I= P/V*PF
=1200*1000/1.732*433*.=1600A
So cable size required if copper cable
1mm=4amp= 400sqmm(by consedering all factors)
For aluminium cable
1mm=2.5A=640sqmm
Generally HT cable sizing is not done based on the full
load current of the equipment but based on the prospective
fault level. For a 11kV network, generally it shall not be
less than 150sqmm XLPE.
Fault level at 11kV(furnished by respective EB)=100 MVA(say)
Details on EB's fault level can be obtained from EB.
Therefore fault current= 100*1000/(SQRT(3)*11000)
= 5.25 kA
Short circuit current rating (for 3-sec duration)of HT 11kV
XLPE cables with Alu conductor is as below:
95 sqmm: 5.16 kA
120 sqmm: 6.51 kA
150 sqmm: 8.14 kA
First calculate the current of primary side(HT) and derate the cable by atleast 0.7.
Eg:1500*1000/(1.732*11000)=78.73A
Current I after Derating =78.73/.7 =112A (0.7 if laid on the trays or value will vary if buried in the ground).
Cable equivalent to rating has to be selected.
Now Short circuit withstand capacity (sq. of I X t in sec) has to be checked from the cable catalogue.This value of cable should be higher then SC withstand capacity of the ground usually it is 50KA.it less go for next size and finalise.
when an induction motor runs on load.at that time if we
reduce the supply voltage the current increases.But when it
runs without load,if we reduce the supply voltage the
current also reduced.why?.i checked it practically also.
11 kv metering is done in my factory.Meter show PF 1.000
but kvarh lag&lead show 24&94 respectively & Avg.PF
is .956 .? is what i do for inproove my PF to 1.000
hi i am aziz electrical associate engineer. i am faceing
problem in acs800 vvvf drive.it is tripping wothout any
alarm/fault.i cheaked all parameters and fault function of
drive, all are correct as well as communication
parameters.but still it is tripping (drive is tripping in
running position not in starting)
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