Example 2 – Selection & Sizing of solar DC Fuse


Let’s consider a project with a four-string configuration. We have an array of 16 modules connected in series in a string.

System Configuration
Module Specifications


Step 1: Requirement of Overcurrent Protection Device

Requirement of overcurrent protection device (or a DC Fuse) is assessed by using below formula

[(Ns – 1) x Isc_mod] > [Imod_max_ocpr]

Putting values of parameters as provided in the problem :

[(Ns – 1) x Isc_mod] = [(4 – 1) x 12.28] = 36.84 A

Imod_max_ocpr = Max Series Fuse Rating = 20 A

Since, 36.84 A is more than 20 A, the above condition is met.

Hence, there is a requirement of an Overcurrent device or a Solar DC Fuse in the system .

Step 2: Sizing of Overcurrent Protection Device

Current rating of the DC fuse as per IS/IEC 62548 should be computed using below mentioned three conditions:

  • In > 1.5 x Isc_mod > 1.5 x 12.28 > 18.42 A
  • In < 2.4 x Isc_mod < 2.4 x 12.28 > 29.47 A
  • In <= Max Series Fuse Rating <= 20 A

Hence, Current Rating of the Fuse should be 20 A

Voltage rating of the DC fuse should be :

Voltage rating of the DC fuse > Max Voltage of the String

Voltage rating of the DC fuse > Voc of Module x Number of Modules in a String > 51.7 V x 16 > 827.7 V

Hence, we will select a 20 A, 1000 V Solar DC Fuse on each string.

For a video of the same article use the link: https://youtu.be/dK09KxYg8Gc

For any suggestions on the topic please write us at info@solarsaarthi.com.


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