Mercury arc rectifier.

[emeritus]

The first (circa 1960) generation of electric multiple unit trains on the Lea Valley services from London Liverpool Street, and services around the Clyde in Scotland, used on-board Mercury arc rectifiers to obtain their DC traction current from the 25kV AC supply, later changed to silicon rectifiers.

[Richard_FM]

Some of the earlier AC electric locos (83 & 84 I think) had Mercury arc rectifiers which proved to be troublesome & replaced with germanium ones.

[kalee20]

Hmm. Yes I can imagine that a liquid-state rectifier might have had issues on a moving, jolting, going-round-corners-fast application!

[The Philpott]

The 'Glass versus UV' discussion came up recently when i was shifting stuff around in a glasshouse under strong sunlight. As is often the case the answer wasn't straightforward- ie what sort of glass....and what sort of UV...what type of effects- tanning, burning, skin atrophy or eye damage.

It's perhaps a sign of the times that urban explorers 'Urbex' are becoming the only ones to see MAR's and similar equipment in their natural habitat. By and large there is adherence to 'no forced entry,leave nothing but footprints, take nothing but footage' and if they use a video camera often the material is made public. At the very least this documents old installations before someone decides to demolish then build 200 houses on the plot. It's a small step in rectifying the cultural vacuum in modern living..

Dave

[kalee20]

Originally Posted by The Philpott

It's perhaps a sign of the times that urban explorers 'Urbex' are becoming the only ones to see MAR's and similar equipment in their natural habitat. By and large there is adherence to 'no forced entry,leave nothing but footprints, take nothing but footage' and if they use a video camera often the material is made public. At the very least this documents old installations before someone decides to demolish then build 200 houses on the plot. It's a small step in rectifying the cultural vacuum in modern living..

Dave

Love the puns

[Synchrodyne]

Originally Posted by kalee20

Hmm. Yes I can imagine that a liquid-state rectifier might have had issues on a moving, jolting, going-round-corners-fast application!

Most traction applications used single-anode pumpless MARs, mostly of the ignitron type. Westinghouse developed a “tractionized” version of the ignitron, first deployed in 1949, then cross-licensed the technology to GE. There were one or two multi-anode locomotive installations, but most of these were experimental. Excitron single-anode MARs were also used, mostly by SNCF, France and JNR, Japan, and SNCF retained this type for regenerative locomotives into the era when silicon rectifiers had otherwise displaced MARs. The traction ignitrons and excitrons presumably had greater immunity to the high short-term accelerations and jerks prevalent in railway service.

Whilst not trouble-free, these single-anode traction MARs were evidently considered adequate in the 1950s. Their advent more-or-less immediately stopped the further development and application of single-phase commutator motors for 25 Hz systems, and whilst there was some development of 50 Hz commutator motors during the 1950s, this quickly fell away in favour of MAR-based AC-DC locomotives. Of course, by the early 1960s, traction-suitable solid-state rectification became available and quickly displaced MARs, with quite a bit of retroactive conversion.

The point is that despite the fact that traction MARs are remembered mostly as being troublesome, for close to a decade they were the technology of choice for new as well as established railway AC electrification systems. The MAR was certainly versatile, and more broadly the “valve story” as it were encompassed production traction applications. (And those railway ignitrons and excitrons were usually metal rather than glass encased.)


Cheers,