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String box 1kV DC/280A

Photovoltaics is currently one of the greenest systems for the production of electricity from renewable sources. For this reason, engineering invests in the study and set-up of products that make this solution usable.

The Engineering Hub of C.R. Technology Systems actively contributes to the energy transition by creating technologies that comply with these new needs:

  • High-voltage substations, which allow utility-scale photovoltaic plants to connect to the grid;
  • Transformation Cabin;
  • String Box.

String Boxes represent one of the most important elements in a photovoltaic plant. They are grouping boxes of strings, designed to convey the electricity coming from the photovoltaic strings and direct it to the inverter which will convert the current from direct to alternating. These boxes are placed in the field, usually hooked to poles of the support structures of photovoltaic panels.

The inputs are the solar cables, coming from the photovoltaic string, which are inserted into the box through MC-4 connectors, while the outputs are two low voltage terminals that will go towards the Transformation Cabin.

The String Box includes the following electrical devices:

  • Fuse holders equal to the number of inputs (up to 32) that intervene in the event of overcurrents
  • Disconnector that ensures the absence of voltage to carry out maintenance activities in safety
  • Surge arrester for the protection of the box in the event of a lightning strike

In some plants in Italy, the arrester has been replaced by a low-voltage circuit-breaker in direct current, equipped with a shunt relay capable of opening the switch if the emergency button of the respective Transformation Cabin is pressed.

String Boxes are “smart” as they support the Operation & Maintenance service to monitor the production of strings and to detect any faults. The shunt ensures a direct measuring for more accurate monitoring, which has a zero-insertion input terminal, where it is connected to one or more strings. The measuring through the hall effect transformer is less precise but guarantees its continuity. The communication of the intelligent String Box with the cabin SCADA can take place via RS-485 cabling, or via a wireless solution with distances up to 15km.

Case study

C.R. Technology Systems has studied and tested a String-Box with proprietary technology, customizable according to customer requests.

Herewith under two of our key projects: