Friday, August 14, 2009

City Street SciFi

In a lane off Little Collins Street, deep underground, is the Russell Place electrical substation. It is a particularly notable place because it has a working mercury arc rectifier, the last in Melbourne I believe. The substation was built in 1882, making it one of Australia's earliest.

When I say working, it doesn't actually supply power any more but has been kept operational for historical display purposes. So what does it do? Or did?

I don't know much about electricity. Here is what I think is right. AC, alternating current, is the type that comes out of your power point. This was not always the case. Maybe not in Australia, but some homes were powered with DC, direct current. I don't know why DC was preferred over AC, but it was, especially for powering lifts, trams and trains, machinery such as a wool press, pumps and other heavy equipment.

Electric substations for Melbourne trams were sprinkled around the city. They converted 240V AC to 600V DC. Some of the substations used mercury arc rectifiers to make the conversion. They were like a giant blue lit light bulb and contained mercury. As the power required waxed and waned, the lamps grew brighter or duller. The more power being drawn, the harder the rectifiers worked and the brighter they glowed.

If you have been around for a while, you might have ridden on an old W class tram and when they were out near their suburban termini and the power supply was low, you could see the interior lights get brighter or duller as the driver cut on or cut off power or other trams in the vicinity did the same. Back at the substation, the rectifier would have been doing the opposite to the tram lighting.

Now this might all sound very much old stuff, but it isn't that old. The mercury arc rectifier in Russell Place was still working in 2003 supplying DC current to the lifts in the nearby Victoria Hotel in Little Collins Street.

Here is the substation, such an innocuous looking building, but below ground level, it is massive with several levels.

Below is a Youtube clip by JennaDDDD. She? states it supplied 750V DC, but I think it was 600V DC for trams at least. I am sure I have seen one of these in the Tardis. Maybe Tardis is powered by 600V DC.


  1. Wow, that is fucking cool! It's like a sci-fi nerd's multiple-orgasm wet dream!

    Can I touch it?

  2. You can touch it gently Mutant. Break it and mercury will be everywhere.

  3. Anonymous11:36 pm

    Old technology, but fit for purpose. Trams still run on DC, a legacy of that time, but the mercury vapor rectifiers - long gone. Doubt if the one in the substation is anything but a prop, fired up when they have open days.
    The problem used to be that it was very difficult to speed control AC motors, but DC motors were easy - so, the trams, trains, lift motors (ie, anything that needed to be speed controlled) were run on DC. DC is terribly inefficient as a means of power distribution, so AC is used. 3 phase AC rectified will give you 600-700vdc. (cant remember the math) so the rectifier units were located as close as possible to the feed point to decrease transmission line losses.
    Nowadays, speed control of 3-phase AC motors is easy due to modern electronics, (called VFD's - variable frequency drives) the mercury vapor rectifiers have been replaced with silicon diodes which are much more efficient, ie no need to waste power in vaporising the mercury. And, mercury is a toxic material, not nice to breath the fumes, gives you brain damage - they need to be run up carefully from cold otherwise they explode - remember the Mad Hatter in Alice in Wonderland who had the shakes - hatters used to use mercury to "block" hats, so constant exposure eventually killed them by eroding the synapses in the central nervous system.

    Michael (a specialist in useless trivia - never pulled anyone at a party using such lines, but it interest me, anyway)

  4. Ooooo, shiny!!!!!!!

  5. Michael, they are not that long gone. Yes, the one in the substation is a prop. It is artificially loaded. So that is why DC was used, to control speed. Makes sense. Yes, mercury is dangerous. Ask the people of Minamata in Japan. Oh, there are none left.

    A shiny bauble hey Jayne.

    I reckon so too Cazzie.