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
0.094

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.

Regards

Sudhanva Madhukar Mahamuni
electricmahamuni@gmail.com

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.

What is the formula for calculating transformer Efficiency?

2 Answers  

---

what will happen if instead of neutral we use earth wire as return conductor?if we can use ,then why we are not using in our day to day appliances?please justify the answer

11 Answers   NTPC, ONGC,

---

v/f drive basic princeple

0 Answers  

---

describe the fully control circuit diagram of ac drives

0 Answers  

---

why phase & neutral is use in tv? why earthing not use ?

2 Answers  

---

WHAT IS THE USAGE OF Buckoltz relay IN POWER TRANSFORMER AND AND HOW ITS FUNCTIONS?

3 Answers  

---

why power is generatd at 50 hz only..? can we do this on another freq...?

7 Answers  

---

If we tell 60 sq.mm. 3-1/2 core cable,then what does it mean ? 1) Each core section in the whole cable is of 60 sq. mm. 2) The whole cable is of 60 sq. mm. which is sub-divided into 3-1/2 core.

3 Answers   Cura HealthCare,

---

can u please mail me the syllabus for GET exam for damodar valley corporation?

0 Answers  

---

What is the form name of 'c' license, I want to download in web

0 Answers   BMM, Ceebros Hotels,

---

Will any motor burn if voltage provided is lesser than the rated voltage???? If yes, then how is speed control possible with voltage control

0 Answers  

---

we have provided 30 mA rccb to water cooler.but we feel shock in cooler body.what is the reason?

3 Answers   FCC,

---