Sunday, May 15, 2011

One flash or two?

While sitting in the lounge room at the Highrise in the evenings, flashes from down below reflect from our blinds. Since the speed/redlight camera has been installed, we have seen many flashes; the camera takes two shots, two flashes.

But another flash has appeared, a single flash. I investigated thoroughly and intensively, by taking my drink out onto the balcony.

The tramway authority has done something to the wire that is in front of the Highrise, but only the wire for the trams going to the city, not the outbound ones. Where the tram pantograph meets the overhead wire, an electric flash occurs as tram passes. The flash is quite a pretty colour but it does not happen every time. This is curious. With trams passing the Highrise in huge numbers, I get to know about them, especially their roofs and overhead wiring and the pantograph things. Maybe there is something on the wire? I never think to look in the daylight and it is a bit far away to see properly. I wondered if some variety of tram flashes and some don't. That would be odd and after study, no matter what variety of tram it is, it flashes, or does not.

I have worked it out now. The flash happens when the tram is under power. If the tram is coasting, no flash, as it not drawing the electric power. There is never a flash from the trams going the other way. Why has this flash device been installed?


  1. The number of flashes is in direct relation to the amount you have been drinking...

  2. What a pity it's the tram system and not someone who's "flashing"!


  3. Quite possibly correct Stephen.

    I have a story about that Peter. I'll write about it soon.

  4. Put on the tin foil hat, the Martians are signalling the mothership... :P

  5. Hi Andrew,

    Having a background in electronics helps me to understand whats going on with your flashing tram power wire. I will try to explain.

    An electric motor like those in the trams, has windings which form electromagnets when power is flowing through them. One of the effects of a coil of wire with a current flowing through it is, it does not 'like' the current to change suddenly. An effect called Inductance. When you try to break the current in a circuit like this, a large voltage spike is produced as the electromagnetic field in the motor starts to collapse.

    The spot in the overhead cable is probably an insulating join which is keeping 2 sections of the overhead electrically separate from each other, this would be so one length of track gets its power from one substation, and the track the other side of the join gets its power from a different substation.

    I remember years ago, the tramways used to install little round yellow signs hanging from the overhead, with the words "CUT OFF" on them, meaning the driver should cut the power to the motors when crossing that part of the overhead wire.... sadly another feature that has gone missing from our tram system, along with the key operated time clocks beside the tracks. Anyhoo, in days of old, this section of overhead would have had one of those signs so the passing trams would not produce the flash / spark / radio and TV interference, and not burn bits off the overhead cables! The green of the flash is copper being vaporised!

    I like Jayne's answer though, better put the foil hat on just in case.


  6. Maybe you could sell balcony viewing space for a new urban phenomenon (damn, I can never recall how to spell that!!)?? Downside is you'd probably have to supply drinks ...

  7. Jayne, I can take them out from the balcony.

    That all makes sense Pip, but normally the insulators are on both in and out wires. Why not in this case? I haven't noticed for a while, but I think some of the cut off discs are still hanging around. There is another disc, with a black cross. I was once told it was where someone had been killed by a tram, but maybe it is just a danger alert.

    Nice idea Red, but seeing a tram overhead wire sparking as a tram passes is no novelty to us. This one is just a bit unusual.

  8. Yeah, but your 'ordinary' is someone else's tourist attraction!!!

  9. It was made to flash so that you could ponder it a while :)

  10. I suppose it is Red. I suppose to someone who has never seen trams, the sparking on wires must look dramatic and dangerous.

    And it succeeded Fen.