BTH Rectifier
The machine shown in the reference was designed by Read and Gimson et al., at British Thomson-Houston (BTH) Rugby, Warwickshire, England, in the early 1950s. It is a three-phase mechanical rectifier working at 220 volts and 15,000 amperes, and its application was the powering of huge banks of electrolysis cells.
The central shaft was rotated by synchronous motor, driving an eccentric with a throw of about 2mm. (0.077 inch) Push-rods from this operated the contacts. The timing was critical, and was adjusted by rotating the position of the eccentric on its shaft, and by sliding wedges between the eccentric and push-rods.
Crucial to this system were the commutating reactors, inductors that ensured the contacts closed when the voltage across them was small, and opened when the current was small. Without these, contact wear would have been intolerably heavy. These were series inductors that operated for most of the cycle with saturated cores. When the current decreased below that for saturation, their inductances reduced the current considerably. Contact switching was timed to occur while their cores were un-saturated.
In the USA, similar rectifiers were made by the I-T-E circuit breaker company.
This machinery was undoubtedly successful; its efficiency was determined to be 97.25%. Contact life was never fully determined but considerably exceeded 2000 hours. However, the rapid development of the silicon diode made it ultimately redundant.
Read more about this topic: Mechanical Rectifier, Motor-driven Type