Voltage conversion on the fly

[Kiha66]

I came across an interesting video tonight explaining how electrified trains in Japan can switch AC/DC and AC/AC overhead power systems without stopping.  Seems the train enters a Zone where one power car passes through an insulated "dead zone", the overhead conduits mechanically switch from one type power system to the next.  The car then coasts (or in case of multiple power cars gets pushed) into the next powered section, where the car is already set to receive the different type of power feed.  A very ingenious solution to the vexing problem of differing power feeds. 

 

 

[Kiha66]

And another video, this time from the JR East Railway Museum in Saitama where they have a 485 series motor car preserved so that they operate the rooftop equipment.  You can see the fast switching action intended to minimize arcing as the car goes from AC feed to DC, and vice versa.  You can tell which side is DC due to the cylinder after the insulator, which is most likely some kind of inductor acting as a choke for the inrush current. 

 

[Kiha66]

Also notice on the diorama how the insulated section of the catenary is longer than a train car.  I assume this is to ensure that even cars (or locomotives) with two pantographs will always have time for the entire car to be electrically dead, keeping any electrical arcs out of the car equipment and ensuring most wear happens at the replaceable contact strip on the top of the pantograph.  A downside of this is that the car will monumentally loose all power other than emergency lighting.  The conductor will announce the blackout a few moments before to avoid passenger worry.  This can be seen in the following video, where the conductor announces the momentary power loss then 30 seconds later the lights go dark for a few seconds.  Fascinating stuff!

 

Edited May 19, 2018 by Kiha66

[Kiha66]

The wiki.jp article on dead sections, with a helpful list of all the ones in Japan with their corresponding voltages and types. 

https://ja.wikipedia.org/wiki/デッドセクション#日本の主なデッドセクション設置箇所

 

And a few technical diagrams for those interested
https://astamuse.com/ja/published/JP/No/1999069505

[kvp]

I would like to add that older units had two different pantographs, one for AC and one for DC, often quite different designs due to isolation requirements and one went down before the end of one section and the other went up on the other section. This was superseded by the common AC/DC pantograph and the manual control got replaced with trackside signalling so dead sections could be reduced from full train lengths to much shorter. Also static inverters, battery backup and trainwide power buses mostly eliminated the power gaps. This could even allow the whole train to retain traction power across the gaps.

[JR 500系]

Interesting stuff indeed.... and I would like to say what a great diorama the first video has done! Really realistic and impressive! 

[Khaul]

5 hours ago, Kiha66 said:

I came across an interesting video tonight explaining how electrified trains in Japan can switch AC/DC and AC/AC overhead power systems without stopping.  Seems the train enters a Zone where one power car passes through an insulated "dead zone", the overhead conduits mechanically switch from one type power system to the next.  The car then coasts (or in case of multiple power cars gets pushed) into the next powered section, where the car is already set to receive the different type of power feed.  A very ingenious solution to the vexing problem of differing power feeds. 

 

 

 

Oh, that's a Cygnus video. Be careful, they are a bit addictive 🙂

 

[ToniBabelony]

Ah yes, the voltage change. That happens on the Mito Line as well after exiting Ōyama sta. for Tomobe. The now retired 415-1500 series would have the blackout, but the E501 and E531 series have negated that issue. A bit unfortunate, as I kind of liked the idea of the voltage change as a transition from the big city connection line (Tohoku Main Line) to the rural life.