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Calculate Short Circuit Current of any Transformer in just 3 steps

Calculate Short Circuit Current of any Transformer in just 3 steps 1024 576 Gaurav Joshi

In this tutorial I’ll explain three simple steps to calculate short circuit current of any transformer. It will also help you in deciding circuit breaker rating. So, let’s start !

Step 1

Get the following details
  • KVA/MVA rating of a transformer (for understanding purpose assume it is 100KVA)
  • Secondary Voltage (Assue 440 volts)
  • % Impedance (You’ll get it from the name plate of transformer, for our example assume 5%)

Step 2

Calculate Full Load Current

For 3 phase transformer, use following formula

I_{secondary}={KVA \times 1000\over \sqrt3\times V_{secondary}}

For 1 phase transformer, use following formula

I_{secondary}={KVA \times 1000\over \ V_{secondary}}

Let’s calculate full load current in our example.

I_{secondary}={100 \times 1000\over \sqrt3\times 440}=131.21A

Step 3

Calculate the short circuit current

We’ll now calculate the actual short circuit current using the following formula.

I_{SC}={I_{Secondary}\over Impedance or Z}

I_{SC}={131.21\over 0.05}

I_{SC}=2624.2A

So, this is our Short circuit current. This will help you to decide the rating of circuit breaker. In this case you need a breaker who’s fault current breaking capacity is more than 2624.1A or 2.6kA.

You can also calculate primary current of any transformer in just 2 steps, to know more about it, click here.

Gaurav Joshi

Gaurav, also known as TheElectricalGuy, is an accomplished electrical engineer with over 8 years of experience in the high and medium voltage switchgear industry. In addition to his professional endeavors, Gaurav has made significant contributions to the global electrical engineering community through his highly successful YouTube Channel. With over 195K subscribers and a prestigious silver play button from YouTube, he has become a trusted resource for electrical engineers worldwide. Gaurav's dedication to sharing knowledge extends to the creation of comprehensive courses, which have already attracted over 3000 students eager to enhance their skills in the field.

All stories by: Gaurav Joshi
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