Selecting DC protective fuses for solar systems: Currently, solar systems are gradually gaining popularity because of their low installation cost, high economic efficiency, and easy construction and installation.

Selecting DC protective fuses for solar systems: Currently, solar power systems are gradually gaining popularity because of their low installation cost, high economic efficiency, and easy construction and installation. However, in the process of designing and installing, the designer also has many concerns in choosing equipment, deciding which equipment is necessary, when to install this equipment, and when not to install it. In this article, Solar INS gives a method to select DC fuses according to IEC 62548. Solar INS Hope to receive comments from the Solar Power community to complete the calculation method.

– First, we need to determine that we use DC fuses to protect DC conductors, PV modules… from short circuits. However, it is not always necessary to use a DC fuse for your solar system. Sometimes it does not help but also brings bad effects to your system.

– So when to use DC fuse when not?

The answer here is to use DC fuses only when the short-circuit current is greater than the conductors can bear.

a.In case of 1 string:

The short circuit current is approximately the working current of the module => no need to use a DC fuse.

b. In case of 2 strings in parallel:

The short-circuit current from the non-short-circuited string to the short-circuited string is determined:: I_max = 1.25*I_sc.

 If our conductor is selected according to IEC 62548 clause 7.36 then:

I_{conductor tt} ≥ 1.25*I_sc*(number of strings in parallel-1)

Assume I_sc = 10A

If you choose dây 4mm²  wire with (I_dd ≈ 15 đến 20A)

In this case I ≥ I_max => No need for fuse protection.

c. The case of 3 strings in parallel.
Short circuit current from 2 strings without short circuit to string maximum short circuit is determined: I_max = 1.25*2*I_sc.

Assuming this case I_sc = 10A, if we use a DC wire of size 4mm² (I_dd ≈ 15 đến 20A)  it is necessary to use a DC fuse to protect the conductor because in this case I_max = 25A >Idd. Selected fuse size:

1.5*I_{sc_module} ≤ I_{cầu chì} ≤ 2.4*I_{sc_module} ( theo IEC 62548).

 15A ≤ I_{cầu chì}  ≤ 24A

Similar calculations for other cases.

Installing protective equipment for your solar system is necessary, but don't let imaginary dangers affect the design and quality of your system.