Answer / ariel

- Draw the per phase diagram of the system
- Express all impedance in per unit values
- Choose a common MVA base and express all Zpu on the
selected common MVA base

Znew= Zpu(MVA base/ MVA)
-Calculate the total per unit impedance of the system
using circuit principle
- Calculate the fault power
MVA fault= MVA base/ Z total per unit

I fault = MVA fault/ 1.73* V

Answer / mak

The fault current of a power transformer will depend on the following;
Transformer Rating (in KVA/MVA)
per unit impedence of the transformer (%p.u.)
line/phase Voltage (VL/VP)
the following formula can be used to find the fault current on the secondary side of a transformer
Fault Current = Transformer Rating /(per unit impedance x phase voltage)

The Values of Transformer Rating, per unit impedance & phase/line voltage will usually be mentioned on the transformer rating plate / data sheet
As an example a 500kVA, 11kV/400V/3-Phase/50Hz transformer with 5% p.u impendence will have the following fault levels on the secondary side

Fault level = 500/(5%)=10000kVA


Fault current = 500/(5% x 400 x 1.732) = 14.4 kA

Remember to use 3phase voltage!

What is the difference between relays and contactor construction wise?

0 Answers  

---

Dry type transformers

0 Answers  

---

Based on what the rating of machines are provided??(ANswer should in single word)

19 Answers   Asian Paints, Bhel,

---

AC covered area by ton calculation

2 Answers  

---

I am an electrical engg and has got selected in wipro should i go there now or try in some core company ?

3 Answers   Wipro,

---

What happen in ups if phase reverse?

0 Answers  

---

what is 400kv doble circuit quadpole tower?

0 Answers  

---

is it possible to flow currnet between earth and nutral wire in a circuit???

2 Answers  

---

how many types of cbs?with pcific ratings?

1 Answers   Bhel,

---

In some countries it is found that an Earthing Transformer is connected at the LV sides of the Transmission and Distribution Substation Transformers.Actually what is the purpose the Earthing Transformer?

1 Answers  

---

How to measure size of cable on a given load

0 Answers   Green India Engineering Solutions,

---

is that any software calculator to calculate the size of cable

0 Answers   JSW,

---