10Hp, 3-phase, 415v, 50Hz induction motor. The above motor is to run on Star-De

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.

Question Posted / girish bodhale

1 Answers
5836 Views
Engro, I also Faced
E-Mail Answers

10Hp, 3-phase, 415v, 50Hz induction motor. The above motor is to run on Star-Delta connection, so h..

Answer / 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.

Is This Answer Correct ?

6 Yes

0 No

Post New Answer

More Electrical Engineering Interview Questions

WHY CAN WE NOT CHAGE SPEED OF SYNCHRONOUS MOTOR...............................JUSTIFY

2 Answers ISMT,

what are the disadvantages in GIS over AIS

0 Answers Tata Steel Limited,

difference between local breaker backup relay or backup protection relay ?

1 Answers

there is a line fault some where on the ove head distribution line. how will i locate the fault for clearing it? ofcourse i have to megger the line but what information makes me clear that the fault is in that section of the line?

2 Answers

1. Can a 12v DC choke operate a 60v/12w PL lamp ? 2. Can a 230v ballast fire / operate a 60v/12w PL lamps.

0 Answers ICS Integrated Computer Solutions,

whati s the sludge current in ups

0 Answers Future Group,

After synchronizing the running generator with grid, the avr getting tripped and the generator breaker also oettong tripped, before tripping the avr the pf meter of generator is showing leading pf please kindly give a suggestion to rectify this problem.

2 Answers Thermax,

WHAT IS counter flux IN CT?

0 Answers

plz explain the auot-reclosing circuit in electrical engineeing

0 Answers BMC, KFC,

what are the protection equipments used betbeen HT line and transformer in a power plant

4 Answers

How is the speed of a DC shunt motor related to the armature current?

0 Answers GE,

what is Wave Trap? And its Function ? Detail? Where it is Used?

7 Answers

For more Electrical Engineering Interview Questions Click Here