Why short circuit calculation is not required in LT cable
sizing and requiredin HT cable sizing only

Answers were Sorted based on User's Feedback

Why short circuit calculation is not required in LT cable sizing and requiredin HT cable sizing on..

Answer / sudhanva madhukar mahamuni

Generally LT Cable size are not calculated based on Fault current basis, Due to High Fault current on LT System. For e.g. consider that 2500 kVA Transformer, %Z = 6.25%, 415 Volts at Secondary. Fault Current at Secondary system will be 55.64 kA. Now if we would have to select the Cable size based on Fault current then it would be ---
If √t
A = ----------------- Sq.mm --- For XLPE Cable Aluminum Conductor

585 sqmm, nearest standard rating of cable is 630 sqmm. Hence Commercially as well as laying point of view the same is not recommended nor as per good engineering practice.

HT Cable Sizing :

Cable sizing based on Fault current is possible In HT System, based practically and commercially point of view. Consider that 11kV system is feeding the power supply. As per IS 2026, 11kV Power system will have max 500MVA Fault Level. It means it will have 26 kA. 300sqmm cable will be sufficient to withstand 26 kA for 1 Sec.

Summary : System Design shall not be strictly as norms, it should be design considering Laying / installation, Practically and Commercially viable.


Sudhanva Madhukar Mahamuni

Is This Answer Correct ?    0 Yes 0 No

Why short circuit calculation is not required in LT cable sizing and requiredin HT cable sizing on..

Answer / xyz

Short Circuit withstand capacity is to be checked for HT
cables. For LT breaker controlled motor feeders, the cable
impedance reduces short circuit current considerable, hence,
short circuit withstand capacity is not required to be
checked for the rated fault level of the LT motors.

Is This Answer Correct ?    2 Yes 4 No

Post New Answer

More Electrical Engineering Interview Questions

i karmveer bharti persuing b.tech . plz send me syllabus and name of reference books. for preparation of section eng.

0 Answers  

what is pressure relief valve in D.G ?state its function?

3 Answers  

How is the percentage impedence of a transformer fixed at design stage???

0 Answers  

Why collecting electrode of ESP to be earthed

0 Answers   NBVL,

what you mean by vector group of a 3 ph transformer

1 Answers  

what is tpmo switch

3 Answers  

please tell 1 ton equal to how many kilo watt?? in some converter software's that is 3.5 kw. is it right?

8 Answers   Mitsubishi,

What is the difference between diode and a transistor in terms of the direction of current flow?

0 Answers  

1 no. 22 kV feeder is taken from state electricity board. 350 MVA is the S.C. MVA. now i am feeding this feeder to HT Panel having 2 outgoings which further supply to 2 Transformers. Can you please suggest me the type & rating of cables are 3 of these cables same? or they are different? please help...............

2 Answers   TCE,

If any one's require of phoenix contact like( relay , termilnal block , surge protection device ) , product please contect me 09878206357 chetan verma

0 Answers  

Whats the diference between Induction motor and servo motor

3 Answers   Essar, PMT Machines,

why 3 phase motors are preferable over single phase motors ?

4 Answers  

  • Civil Engineering Interview Questions Civil Engineering (4645)
  • Mechanical Engineering Interview Questions Mechanical Engineering (3704)
  • Electrical Engineering Interview Questions Electrical Engineering (15785)
  • Electronics Communications Interview Questions Electronics Communications (2638)
  • Chemical Engineering Interview Questions Chemical Engineering (762)
  • Aeronautical Engineering Interview Questions Aeronautical Engineering (79)
  • Bio Engineering Interview Questions Bio Engineering (30)
  • Metallurgy Interview Questions Metallurgy (95)
  • Industrial Engineering Interview Questions Industrial Engineering (199)
  • Instrumentation Interview Questions Instrumentation (2882)
  • Automobile Engineering Interview Questions Automobile Engineering (171)
  • Mechatronics Engineering Interview Questions Mechatronics Engineering (41)
  • Marine Engineering Interview Questions Marine Engineering (62)
  • Power Plant Engineering Interview Questions Power Plant Engineering (170)
  • Engineering AllOther Interview Questions Engineering AllOther (1336)