Electrical Cable section calculation

[Hakim Eng]

Hello guys,
i have a 15 KW three phase motor situaded at about 600 meters away from the power source, which cable section do i need to use ?
thanks in advance

 

[waross]

#2 AWG copper cable and raise the voltage until full load current drops below 90 Amp.
Edit: My bad. I slipped a bunch of decimal places. Should be:
#12 AWG copper cable and raise the voltage until full load current drops below 20 Amp.
Thanks for overlooking my stupid mistake, Mr. Che.
or
Hire an expert. If you need help with cable size for a 15 kW motor, you need more help than you will ever get over the 'net.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. Hakim Eng (Electrical)
1. Your information is inadequate for anyone to give a useful answer. Please advise the following basic data:
a) power supply voltage(V): [single-phase or three-phase], frequency [50/60Hz],
b) motor name-plate data,
c) starting method: [direct-on-line, star-delta, auto-transformer reduced voltage starting etc.] ,
d) location: whether IEC, NEC or local/regional code/regulation to be observed.
2. "... or... Hire an expert. If you need help with cable size for a 15 kW motor, you need more help than you will ever get over the 'net..." as observed/advised by Mr. Waross.
3. DO NOT play around with electricity. You don't see it, smell it but could be dangerous!
Che Kuan Yau (Singapore)

 

[7anoter4]

If you said kW and meters, I suppose you are from IEC World.
If you are an electrical engineer of any kind -not energetical-you better start to learn a local safety standard as BS7671 or VDE/DIN or else.
The nominal system voltage it is 400 V[380-415V as per IEC 60038]
A 4% voltage drop for full load steady state current and 15% for start it is usual.
It will be better if you can see the motor name plate for voltage, current and starting to nominal current ratio.
If it is not possible let's take 400 V,30A and 8.
You can start with 50 mm^2 and find the a.c. resistance and reactance from a cable supplier catalogue [as ABB, for instance] or from BS7671, for instance.
A cosine fi for load it could be 0.8 and for start 0.3.
The voltage drop will be= sqrt(3)*In*(r*cosfi+x*sinfi) or for start put Istart instead of In.

 

[che12345]

Dear Mr. Hakim Eng (Electrical)
Further to my earlier post dated 5 Sep 21 21:30, it is essential to advise:
4. The installation method: i.e. indoor, outdoor, on poles or buried etc.,
5. The type of conductor (i.e. armoured/non-armoured) you intended to use; taking the local code into consideration.
Che Kuan Yau (Singapore)

 

[waross]

Hakim Eng hasn't been back.
It is probably past the deadline for his homework top be handed in.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Hakim Eng]

Thank you so much guys for your replies and precised answers,
i am an Automation Engineer not Electrical Option,
these are the main characteristics of my situation:
- the motor is three phase motor in star connection with power factor of 0.8 indoor installation.
- 50 Hz frequency with 400 v line to line voltage.
- a copper armoured wire.

i am here to learn from you guys and share knowledge.

Thanks in advance

 

[waross]

In Canada there are two steps.
Use 125% of the motor's rated full load current and the ampacity tables in your code book to determine the minimum cable size.
Some codes mandate that the current value be chosen from a Horse Power table so that the wiring will be adequate in the event that the motor is changed for a less efficient motor sometime in the future.
We would use the 75 degree C column for three or more conductors in raceway or cable.
Determine the voltage drop from the voltage drop table. The CEC voltage drop table includes information on extrapolating for different lengths and per unit voltage drops.
Our code limits the voltage drop to 3%
You still haven't provided the rated current of the motor.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Jacob Henry]

To find voltage drop in a cable, follow the simple steps given below.

1. First of all, find the maximum allowable voltage drop.

2. Now, find the load current.

3. Now, according to the load current, select a proper cable (which current rating should be nearest to the calculated load current) from table 1.

4. From Table 1, find the voltage drop in meter or 100 feet (what system you prefer) according its rated current.

(Stay cool We will follow both methods and systems for finding voltage drops (in meters and 100 feet) in our solved example for whole electrical installation wiring).

5. Now, calculate the voltage drop for the actual length of the wiring circuit according to its rated current with the help of following formulas.

(Actual length of circuit x volt drop for 1m) /100 ===> to find Volt drop in per meter.
(Actual length of circuit x volt drop for 100ft) /100 ===> to find volt drop in 100 feet.

6. Now multiply this calculated value of volt drop by load factor where;

Load factor = Load Current to be taken by Cable/ Rated Current of Cable given in the table.

7. This is the value of Volt drop in the cables when load current flows through it.

8. If the calculated value of voltage drop is less than the value calculated in step (Maximum allowable voltage drop), than the size of selected cable is proper

9. If the calculated value of voltage drop is greater than the value calculated in step (Maximum allowable voltage drop), than calculate voltage drop for the next (greater in size) cable and so on until the calculated value of voltage drop became less than the maximum allowable voltage drop calculated in step.

https://mwi.solutions/technologies/wms-wcs-and-oms-software/

 

[che12345]

Dear Mr. Hakim Eng (Electrical)
[COLOR=]"...You had given: 3-ph400V 50Hz 15kW motor; copper armoured cable indoor installation, length 600m. Question is, what size of conductor?..."[/color]
1. But, you did not state the motor I)rated current, II)Ist/Ir or the starting current, III)method of starting, IV) permissible voltage-drop for a)running and b)starting, V)Standard etc.
2. I assumed the following additional data for my calculation:
I)=29A approx; II)=6; III)=DOL; IV a)4%, b)15%; V) IEC, BS7671.
3. Refer to BS 7671 Tables on "Armoured PVC insulation or PLPE insulation " , installed in free air...three or four core cable ... (voltage drop mV/A/m)
4. Due to the long 600m length, try 120mmsq:
a) it would fulfilled the 4% V.D., running at 29A,
b) it would also fulfilled the 15% V.D., on starting at 174A.
5. Please verify and add any other climatical/installation factors etc as appropriate.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr. Hakim Eng (Electrical)
@ All learned peer
1. Please refer to my post dated 12 Sep 21 13:38. All comment/advice are welcome. I need help and peer-review/advice on whether am I using the correct method, which ended up [extremely large 120mmsq cable] for a small 3-ph 400V 15kW motor, located 600m away.
2. I treat the proposal as Plan A. I have some thoughts on how the problem may be mitigated marginally. I have another Plan B which propose a more drastic changes on the design, but hopefully with better savings.
3. I would hold back the refinement on Plan A and Plan B till upon receipt of learned advice from the peer.
Che Kuan Yau (Singapore)