Short Circuit Current Calculations for Symmetrical and Unsymmetrical faults

In this, you will learn how to manually calculate the short circuit current.

Short Circuit Current Calculations for Symmetrical and Unsymmetrical faults

It is not practical to design a power system which is free from failure. Hence we need to design the system which is capable of withstanding the faults till the fault is cleared by circuit breakers. It is necessary to select the circuit breaker which has the capability to interrupt the worst case fault current. In order to do that we need calculate the worst case fault current. This article talks about the calculations of Short circuit current for various faults (three phase fault, single line to ground fault, Line to Line fault and double line to ground fault) for the given
network.

Case 1: Under No load

Grid: 110 kV, Short circuit current of 40 kA, X/R = 14,

Transformer: 25 MVA, 110/11 kV with %Z of 10, X/R = 20

The fault is created at 11kV bus and the fault impedance considered to be zero (Bolted fault).
The step by step procedure and calculations are made below.

Procedure & Calculations:

Step 1: Let us consider 100 MVA and 110 kV as base MVA and Voltage respectively

Step 2: Find the R P.U & X P.U values and validate with ETAP results

Step 3: Convert the Impedance to common base i.e, 100 MVAb

Step 4: Draw the Impedance diagram and find Positive, Negative and Zero Sequence
impedance. Step 5: Calculate the fault current and validate with ETAP results

Not sure how to get started with design engineering? want a free consulting call?

We’ve got you covered!

Fill out the form to get personalized guidance on how to:
✱ Transform your career in electrical engineering
✱ Discover the best tools and software to learn
✱ Identify the next steps to take toward design engineering

Start your journey today!