Solar system design : Over protection

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It is important to protect the solar pv system from over current and voltage fluctuations to get effective output. Solar pv system should have protection device like Dc fuses at string level and array level. Present days in the solar pv system typically about 20-24 modules are connected in series, which results around 700v D.C and 8.3Amp of current.

This article comprises about protection at string level and array level.

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How to select fuse links for string protection:

The current and voltage ratings of fuse links at string level should be 1.56 x Isc and 1.2 x Voc x Ns.

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Example calculation for fuse rating at string:

Let us calculate fuse rating for spv plant which has 4 strings in array and 24 solar panels are connected in series.

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So that fuse rating should not be less than1077v and 13.7A.

Array protection:

A fuse link on each sub-array will protect the conductors from fault current and help minimize any safety hazards. It will also isolate the faulted sub-array so that the rest of the PV system can continue to generate electricity.

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How to select fuse links for string protection:

The current and voltage ratings of fuse links at string level should be 1.56 x Isc x Np and 1.2 x Voc x Ns respectively.

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 Example calculation for fuse rating at array:

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So that fuse ratings should not be less than 55.08A and 1077v at Array level.

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