"Complete understanding of the project requirements as well as clear differentiation in the technical design and implementation of the connectivity solutions: these were the key criteria that we applied in selecting our partners," say Messrs Vendier and Panico from the French engineering group Spie. "And these are precisely the qualities that qualified Weidmüller for our project. The team secured our complete confidence over the entire duration of the partnership by listening actively to our needs and with technical tours de force."
Specific solutions for a record project
1,200 secondary and 300 primary junction boxes with integrated monitoring - this was the requirement made of Weidmüller. Installed between the solar modules and the power inverter, the generator junction boxes combinethe generated currents. They form an optimum connection component and enable the efficient operation of large-scale facilities like the EDF project.
Weidmüller has already developed a number of standard configurations based on recurring customer requirements. However, Weidmüller also implements specific solutions - as was the case with this major project in France - especially adapted to the individual architecture of large-scale facilities.
The secondary junction boxes installed on the photovoltaic modules contain fuses, an isolating switch and surge protection with remote monitoring. They have an output voltage of 712 or 760 V and a current rating of 10 to 70 A.
They are connected via buried aluminium cables to the primary junction boxes, which are accommodated along with power inverters and transformers in local cabinets. Each primary junction box is connected with around 20 to 26 upstream secondary junction boxes and is equipped with modules for measuring the string currents. This makes it possible to constantly optimise the performance of the facility.
The power cables that conduct the input current to the secondary junction boxes are connected to WDU feed-through modular terminals and WFF bolt-type screw terminals with a contact area of up to 300 mm² and are protected by a fuse. The WDU and WFF modular terminals have been certified by Weidmüller for 1,000 V DC applications after a partial discharge test with DC voltage.
The insulation thickness, terminal dimensions or other physical characteristics of the terminals do not, at first sight, seem suitable for DC applications. However, the various characteristics must be considered in combination. For this reason, Weidmüller has certified each modular terminal type individually for this type of application.The output current of the primary junction boxes may be over 1,000 A. Each distributor passes on 33 kV to the switching station located 15 km away, where it is stepped up to 63 kV and fed into the RTE grid.
Development and production in record time
Before production of the equipped housings started, Weidmüller developed prototypes of the secondary and primary junction boxes according to the specifications of Ingérop, the engineering consultancy engaged by EDF. The criterion was that the boxes had to comply with the French regulations for DC and the standards for the installation of photovoltaic facilities as per the practice guideline UTE C 15 712.
"Based on Ingérop's specifications, we have developed generator junction boxes, which are carefully adapted to photovoltaic systems and which are assembled and tested accordingly. This was where we were able to score with our extensive practical and market experience," recalls Weidmüller key account manager, Vincent Fiévet.
"With our familiarity with French technical regulations, we were able to furnish the customer with solutions, which fully complied with the applicable standards. Our prototypes therefore passed the tests in the application with flying colours."
To stay within the tight schedule, production at Weidmüller worked flat out: 30 secondary and five primary junction boxes per day rolled off the production lines in Barcelona between June and November 2011.
"To deal with such a production volume under time pressure requires absolute commitment,“ comment Spie's Vendier and Panico.
"This is where Weidmüller again proved themselves with values that mean a lot to us, such as closeness to the project and proactive acceptance of responsibility. In Weidmüller staff, we have found a partner who has impressed us in equal measure with their can-do attitude and their realism - the optimum combination with a tight project schedule like this."
In addition to Spie, EDF engaged two other companies to implement the project, Clemessy and Ineo. All three companies have something in common: they entrusted Weidmüller with the design, development and production of around 1,500 generator junction boxes in record time - and were ultimately, completely satisfied.