Answer / suresh kumar

The procedure for cable sizing is first to measure the
load in currents and voltage of load which is to be
connected in that particular cable. Then the length of
cable. Type of cable conductor whether copper or aluminium.
Medium of cable passing whether in opened cable tray (air),
closed cable tray, in open land, in cable trunch etc. The
usage of cable also to be taken care, ie like telephone
cable, control cable, power cable etc.
In an example the current rating of 10 sq. mm copper cable
in air is 40Amps. If the length of cable is shorter we can
use it and if the length of the cable more, we have to
calculate the voltage drop of that cable and may be have to
use 16 or 25 sq. mm cable instead of 10 sq mm.

Answer / surendra matharu

I really appreciate the efforts put by all.
I would like to throw some light on the matter.

There are three CRITERIA for cable sizing :
The criteria which gives the worst rating is adopted.

1. The maximum short circuit current which can pass through
the cable.
2. The maximum load current which the load can withdraw from
the system.
3. The maximum voltage drop allowed in the system.

Out of these, whichever criteria gives higher rating, that
is selected.

Hope, this satifies the query.

Answer / abhay

copper cable size for following

Panel Power Cable 63A 300mtr
15 HP VFD Cable x 325mtr
20HP VFD Cable x 325 mtr
10HP VFD Cable x 325 mtr
vfd panel 250 amp *50 meter
cable pass through pvc condut

Answer / raghavendran.r

Thanx to all for giving useful answer on that subject.I
would like to add that cable selection is also influenced
by certain factors like the Derating Factor.

A cables Current carrying capacity is reduced by the
following factors

a) Soil thermal resistivity.

b) Grouping Factor.

c) Ambient Temperature factor.

d) And the Depth at which Cable is to be laid.

Based on All these factor the current carrying capacity is
calculated and that also decides the number of runs of
cable to be laid.

Apart from this what Mr Matharu has stated is taken care of.

Formula to calculate SQMM is

Max short Ckt withstand current*sqrt[T(fault time)] /K.

for EX = 40 KA*sqrt(.25)/(.0928)

Answer / raul

the size of a cable depends upon the maximum dielectric
stress at the conductor surface.........
dielectric stress/potential gradient,g = V/xLOGeD/d
where V= system voltage; x= distance from conductor, D=
diameter of conductor and d= diameter of metallic
sheath....
so max. dielectric stress will b at conductor surface,i.e.
at g(max)= 2V/dLOGeD/d
d value of conductor diameter will be D/2.718 OR LOGe(D/d)
= 1

Answer / oarhe ize

We calculate cable sizes in order for us to know the amount
of load it can withstand (current rating)

what is earth resistance? how to measured? and give values at power station and mcc area?

0 Answers   Essar,

IF 5000amp current on LT 440V. then how much it will draw amp on HT 11KV side

10 Answers  

On what factors the generating voltage depends ? Generating voltage are (3.3kV, 6.6KV , 11KV, 13.8kV) Why so ?

5 Answers   Bhel,

what is the equation of insulating resistance of motor???

1 Answers   Birla,

What are the two basic types of transformers?

0 Answers  

Hi, Next week Iam appearing RRB exam for section engineer. So help me to get modal question papers for this position. Iam very thankful to you. Whether question will be fully techanical format or general form. Please give me a details regarding this exam.

0 Answers  

we have two motors 1250kW,6.6kV to be coupled on the same shaft ,so please provide assistance for their synchronisation.

0 Answers  

i have dry type transformers can you help me that how many tests i can do to know the performence of transformer and also please tell me about the BDV test and Insulation resistance test in oil cooled transformers

4 Answers   Hyundai,

one electromagnet is called

0 Answers  

1. A 380 / 220 V r.m.s. 3-phase 4-wire circuit carries loads of 8 + j8.1 ohm; 4 + j4.1 ohm; and 2 +j2.1 ohmin the three phases respectively. The length of the circuit is 100 m, and the resistivity of the phase conductors is 0.0005 Ω/m. The neutral conductor is of the same size as the phase conductors. a) Select a reference angle 0for the first phase. Then write down the three phase voltages in both polar format and complex number format. b) Make appropriate assumptions, and take temperature effects on resistance is insignificant. Calculate the currents in the three phases. (Note: Determine conductor resistance, and apply Kirchhoff’s Voltage Law) Based on the result, suggest a main switch rating for the circuit. c) Show your preferred direction of neutral current in a diagram, and then determine its value. (Note: Apply superposition principle, and Kirchhoff’s Current Law) Use its magnitude to show that in this circuit, the unbalanced load may increase the voltage drop in some of the phases. (Note: Also observe the common volt drip in neutral) State your assumptions, if there are any. d) Suddenly the neutral wire of the circuit is broken. Estimate the new currents in the first phase, i.e. Phase L1. State your assumptions, if there are any.

0 Answers  

what will happen if field winding supply of synch generator accidently got disconnected?

4 Answers  

If i have 200 test cases and we have to execute but we don't have time to execute all testcases.within 1 hour we have to execute that testcases and prepare the test report.so how i have to resolve this problem? is there is any technique in the testing.

3 Answers   Stag Computers,