Why do japanese electric trains run with all pantographs up?

[martin67]

Hi all,

 

something that haunts me for many years.... With few exceptions, most electric trains in the world run with only one pantograph raised. Normally, it should be the rear one. If this one fails or gets torn off, it won't damage the roof mounted electric equipment and leaves the front pantograph left as a back-up. Exceptions to the rule are (speaking for most railways in Europe):

 

- the first car behind the loco carries flammable liquids, automobiles or a canvas cover (sparks may damage the load), use front pantograph

- a multi-current loco having only one pantograph for each system

- ancient pantograph with only single pick up shoes (pre-WWII locos in Germany)

- limited current draw due to ice on catenary (needs two to get enough power)

- no electric connection between power cars (i.e. 1st generation ICE in Germany)

 

In Japan I've never seen an electric loco with only one raised pantograph. Anybody knows why?

 

Cheers,

 

Martin

Edited September 3, 2018 by martin67

[bikkuri bahn]

You’ve never seen locos with only one pantograph raised because you’ve only seen DC locomotives. AC locomotives in Japan run with only one pantograph raised as at the low current and high voltage of 20kV it’s adequate. *note scenes running with two pantos up, that’s in a DC section, as this loco is dual current.  

OTOH on lines electrified at 1500v DC, the low voltage requires a high current, and two pantographs are raised to handle that high current.  This is not just on Japanese railways, but on other systems using the same system.  For example, the now defunct Woodhead Line in the UK, which also was electrified at 1500v DC:

 

Edited September 3, 2018 by bikkuri bahn

[railsquid]

3 minutes ago, bikkuri bahn said:

 AC locomotives in Japan run with only one pantograph raised as at the low current and high voltage of 20kV it’s adequate. 

 

 

Except when they're dual-mode ones and running on DC of course; note different pantograph usage on the same class of locos (EF510) here:

 

 

[bikkuri bahn]

This is a common  misperception among foreign railfans, probably because DC electrified lines are common (and older) in the more populated regions of Japan, and thus are more photographed and filmed.  Interestingly, most Japanese think of two pantos raised as the norm, and find single panto operation as novel/strange.  

[Sacto1985]

Which explains why JR East E5 and E6 only use one pantograph operating, probably because of their electrical design. The 700, N700, N700A and soon N700S trainsets use two pantographs operating.

[katoftw]

The E5 and E6 only use one pan each when coupled together to save wear as only 2 raised is needed. Once split, they use both.

[kvp]

I would like to add the very common cow-calf arrangement of motor cars, with two motor cars sharing one pantograph. The series 0 shinkansen had this setup too, with each pair of cars having one 25kV AC pantograph, at the end where the pair was coupled. This meant a 16 car train had 8 pantographs up. This strategy was used on many other cape gauge JNR emu-s too, with Mp-M pairs and no through high voltage lines. This means two motor cars share a single DC pantograph. For locomotives with higher powered motors and thus higher current draw, this is often not enough and they need both pantographs in DC mode.

 

In Europe for example, the RhB Allegra railcars use a single pantograph on AC sections and DC sections with lower gradients. Only the high gradient DC section needs both pantographs to get enough current for the trip through steep parts of the Bernina pass. An example video with both single and dual panto mode on the same line:  https://www.youtube.com/watch?v=KJU9bLWqLw4

 

[Kiha66]

2 hours ago, Sacto1985 said:

Which explains why JR East E5 and E6 only use one pantograph operating, probably because of their electrical design. The 700, N700, N700A and soon N700S trainsets use two pantographs operating.

 

Actually all shinkansens use 25kv ac, the only difference here is whether the line is 50hz or 60hz.  The only exception is the Akita Shinkansen as it shares part of the trackage with the ou main line, and as such runs at 20kv ac.

[railsquid]

Exception to the DC two-pantograph rule:

 

 

 

Edited September 18, 2018 by railsquid
fix video start time

[chadbag]

 

@railsquid  So what am I looking for with the "Exception to the DC two-pantograph rule" ?

 

Sorry for being a bit dense.

[Kiha66]

10 minutes ago, chadbag said:

 

@railsquid  So what am I looking for with the "Exception to the DC two-pantograph rule" ?

 

Sorry for being a bit dense.

 

Looks like it was squids mess-up, the time stamp is wrong.  If you go back to the start of the video an earlier locomotive comes through with only one pantagraph up.

[railsquid]

5 hours ago, Kiha66 said:

 

Looks like it was squids mess-up, the time stamp is wrong.  If you go back to the start of the video an earlier locomotive comes through with only one pantagraph up.

 

Odd, dunno how that happened. Fixed.

[kvp]

That was a very short train. On flatland tracks and a light load the loco does not need that much power and could get away with only one pantograph. Even with one working bogie.

[AllScales]

You’ll probably find that in stations the contact wire is doubled. Again this is to allow trains running on 1500V DC to draw the current without melting the wires.

 

If you’re in Japan check what happens overnight in winter, you’ll probably find lots of pantographs up in low voltage yards when low temperatures are predicted....