The construction of the charger was based around two substantial steel fabrications. The main cabinet frame was made from 50X50X5mm and 100X50X5mm wall box section steel, and the top and bottom chassis sections were made up from 10g (3mm) steel sheet, the whole assembly being fully welded throughout. We are grateful to our suppliers for a first-class job in which all parts came together with no 'adjustments' being required!

The whole assembly was then powder coated in semi-gloss black. The doors, corner and centre posts were made up from 2mm steel sheet which was then powder coated in RAL7032 semi-gloss, which gave a nice finish to the assembled cabinet. The control panels and internal chassis were done in gloss white powder.

The main framework arrives from the painters.

Once inside the factory, the main framework had its subframe fitted and the work of assembling the mains transformer and smoothing chokes could take place. The from centre column of the main frame was made detachable so that we could fit the transformer in without being impeded by the column. Cladding panels cover all the framework.

Base of the unit with main subframe in place. Cable access was by 16 gland holes up to 40mm.

Because of the weight of the transformer and chokes, it was decided at an early stage that they would sit on a fabricated subframe, thus relieving the main framework of any stresses relating to their weight and position. While this added extra weight to the finished product, we felt that it would be better mechanically to keep the heaviest items on their own chassis, just as we do in all our other large chargers.

Base of the unit with mains transformer and smoothing chokes in place.

The size of the mains transformer dictated everything else's position in the cabinet, and although we had originally intended to have a slightly different layout, it eventually fell together quite naturally in the final layout that we built, although there were some minor changes made to accomodate access or cabling.

Looking across the charger from the right-hand side, showing the two smoothing chokes.

The fields from the two smoothing chokes would not interact as only one side of the unit would be used at a time, so only one choke would be in operation. Electrolytic capacitors were used after the smoothing chokes to give a low voltage and current ripple figure. Bleed resistors were also used to keep the voltage steady under zero load and to prevent the high voltage cap's remaining charged after shutdown.

Further progress with internal chassis and external corner cladding in place.

The electronics control systems were mounted on two right-angle chassis plates that were mounted in the upper half of the cabinet. Generally it was assembled with the 620V side on the left and 60V on the right, although in practice there was more equipment on the left hand side due to the mains control switchgear being placed there also.

Most of the major parts assembled, with output breakers and thyristor modules in place.

Output contactors were ABB Clapper types, which we have used before with great success. For cabling convenience they were placed side by side, and the available space also had a bearing on their positioning! Blocking diodes on fan-cooled heasinks were position just above them, but not shown in the photograph. A large 10g (3mm) steel tray was bolted onto the top of the mains transformer to house many of the smaller controls PCB's and the PLC enclosure which was supplied pre-assembled by the customer.

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