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10Hp, 3-phase, 415v, 50Hz induction motor.
The above motor is to run on Star-Delta connection, so how
do i make following hardware selection
1) MCB, 2) Contactor, 3) Wire Gage (Depending on P-P current
or Line Current), 4) OLR,
Please tell in detail how to do the above, so as to get the
ans. of it even if the Hp rating changes.
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Answer Posted / 7anoter4
10 hp=7.5 kW. The manufacturer has to indicate the starting
current.
Let's say the motor is designed for star/delta starting
then according to IEC 60034-12 Tab2 for 6.3 kw up to 25 kw
S1=12 then maximum permissible starting current will be
Istart=12*7.5*1000/1.73/415=125.2 A.
The short-circuit protection has to be set at
1.25*125.2=156.5 A.
The circuit breaker rating has to be 150 A. The motor
overload has to be set at 1.25*Irated and also will trip
the breaker if the current of 2*Irated will last more than
the permissible stall time [let’s say 4 sec].
The supply cable allowable current [see IEC 60364-5-52]
shall be 1.25*Irated.
Usually a 7.5 kW motor at 415 V rated current will be 13-16
A then the cable permissible minimum should be 20 A.
According to the above mentioned standard 2.5 mm^2 copper
conductor PVC insulated will be ok.
You have to check the voltage drop also: no more than 3%
rated and 10% at start. If DV=1.73*I*[R*cos(fi)+X*sin
(fi)].R,X =total resistance-at 70 dgr.C- and reactance
[ohm].
cos(fi)=0.85 [approx.] rated and 0.3 at start. Sin(fi)=
(1-cos(fi)^2)^0.5.
In this case if the cable length will be 80 m 4 mm^2 copper
conductor has to be employed.
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