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DC Surge Protective Device SPD connected to installations of photovoltaic systems

Modular multipole surge protection device, arrester for use in PV & DC power supply systems with remote signalling contact for monitoring device (floating changeover contact)

Photovoltaic arrays are costly to install and demanding in terms of technology. Their service life must be measured in decades to see a return on the invested funds. Manufacturers usually provide about a twenty-year guarantee for photovoltaic systems.

To provide trouble-free technology throughout its service life, it is necessary to include comprehensive protection against atmospheric and induced overvoltage at the design stage to implement the technology into the project. Protection must be provided not only at the output side of the inverter but also at the photovoltaic panels.

Solar photovoltaic arrays are usually installed on rooftops, or on a “greenfield“. As for the anticipated risks (pursuant to EN 62305-2), director near lightning strikes is considered. Overvoltage or lightning strike can bring about financial loss, and for photovoltaic systems installed on rooftops where individuals could be working, the injury should also be considered.

Photovoltaic system designs, including lightning and overvoltage suppression, shall comply with the HD 60364-7-712 standard (Electrical installations of buildings – Solar photovoltaic (PV) systems), technical specification CLC/TS 50539-12 (SPD for specific application including DC – Selection and application principles – SPDs connected to PV installations) and the group of EN 62305 standards (Lightning protection).

The core (key device) of the whole photovoltaic system is the inverter, so the lightning and overvoltage protection should be focused on the inverter and, it should be incorporated into the whole lightning and overvoltage protection system. Furthermore, photovoltaic units and their bearing metal structures should be integrated into the grounding design.

SPD selection for DC side:

  • UCPV maximum continuous operating voltage
  • UOC STC standardized test circuit voltage of PV String: UCPV ≥ 1,2× UOC STC
  • If separating spark-over distance “s” is kept – Type 2 SPD PV is installed. If distance “l” between PV modules and inverter is longer than 10m – SPD is installed on both sides of the DC line
  • If separating spark-over distance “s” is not kept – Type 1 and 2 SPD PV is installed. It is always necessary to install SPD PV on both sides of the DC line

The DC side of the PV system can either be unearthed (insulated) or with one pole earthed. Figures 1 and 2 (see CLC/TS 50 539-12) show how SPDs on the DC side must be connected.

When mounting an SPD, the necessary length of the connecting conductors should have complied with HD 60364-5-534 (IEC 60364-5-53, chapter 534), clause 534.2.9.

LSP has designed a complete range of Type 1+2 and Type 2 surge protectors for these applications that are compliant with the EN 50539-11 product standard.

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