Example 2 – Selection & Sizing of solar DC Fuse
Problem:
Let’s consider a project with a four-string configuration. We have an array of 16 modules connected in series in a string.
Solution:
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.
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