|Mercury Arc Rectifiers|
On the 29 June 2010 the mercury arc rectifiers were switched on and loaded to 48 amps, for the first time since 1997 when they were taken out of service at the Covent Garden Opera House. The rectifiers convert the incoming 415 volt 3-phase alternating current to the 200 volt direct current needed to operate various motors on pumps and compressors. Up to now we have used a modern solid state rectifier. When tested the no-load voltage was 242 volts, as expected, and dropped to 203 volts with a load of 2 amps as predicted by theory. The output voltage at 48 amps was 200 volts.
The mercury arc rectifiers originally installed in Triple House were destroyed when the building was decommissioned. A member, attending a planning meeting at the soon-to-be refurbished Opera House learnt that mercury arc rectifiers were being decommissioned and removed, and after negotiation the Opera House agreed to gift them to the Trust. The rectifiers had been used to power the stage lifts, driving First World War German U-boat motors, obtained in reparation.
The rectifiers were transported to Kempton in three parts, the two cubicles, the bulbs in their special crates, and the transformer. When they were first inspected they were in a far worse state than expected for equipment that had been in operation only weeks previously. It is likely that they had been in continuous use for more than 50 years. Every part of the cubicles and wiring was encrusted in oily dirt, the forced-air cooling ensuring that it penetrated every crevice. The wiring was insulated with vulcanised india rubber (VIR ) which had become brittle and no longer insulated properly.
Over the years, Tim Moth and David Walker, with the occasional help of others have painstakingly dismantled, cleaned, refurbished or replaced each part with as close to contemporaneous parts as possible, reassembled and tested. Virtually all the wiring was replaced with equivalent modern cable, sleeved to resemble the appearance of the original, the power transformer was refurbished and new controls were added.
The pictures to the right show the rectifier bulbs in operation and the two restorers.