Tech questions anew: Power control gear on JNR era electrics

[NGT6 1315]

Afternoon all!

 

I was just thinking whether a unified "Basics of Japanese railway stock designs" kind of thread might make sense, but I'll leave that to the moderators!

 

Anyway, I have been trying to understand how electric locomotives built during the JNR era are designed. I'm quite familiar with common European electric traction design principles, but I wouldn't be surprised if JNR had had different ideas entirely!

 

I suppose that locomotives built for the 1.5 kV DC system only would usually have been equipped with rheostatic power control…but were there chopper-equipped locos as well, and if so, which classes would those be?

 

As for AC or multi-system AC/DC locos, I tried to make sense of a Google translation of the Japanese Wikipedia article on the class ED79 locomotives, and seem to have understood that these were equipped with a low tension tap changer on the secondary transformer side, and either thyristor-based (ED79-0 and -50) or mercury (ED79-100) rectifiers beyond that. Would that be the usual power control setup for JNR era AC motive power? I figure that with the technology of the time, building what would essentially have been DC locomotives with added AC components would have been the most straightforward approach, and also allowed for more economic spare keeping.

 

I'd be happy if, again, anyone knowledgeable could help me out here. It's not always easy to interpret the semi-gibberish put out by online translations!

 

Cheers,

Dom

[kvp]

The Japanese railways imported lots of technology from the start, so both british, amercian and even swiss technology found their way to Japan. What is special is that japanse designers managed to combine all of these into unique designs.

 

For DC systems, the most common way was resistor control until various more modern japanse designed system began to appear. For AC systems, the most trival is to use tap changers. especially that it allows various AC overhead voltages and frequencies that are used in various regions of Japan. When you want to make an AC/DC system, you can combine tap changing with resistor control and create universal locomotives and emu-s, that can run on both systems. This requires the use of universal motors or electronic AC/DC converters. Some early systems used the series wound universal motor approach that could be run on both AC and DC, but soon more modern systems appeared that finally led to the use of silicon rectifiers then IGBT and now full FET control first with DC motors and nowdays AC motors are quite popular. Many older units were modernised and got new power bogies and control systems when they became available. This is why some of the older trains have or had all possible traction system variants over the years.

 

The 'classic' JNR locomotives and emus mostly used series wound universal motors that can be powered by low voltage AC and DC and could be controlled with tap changing, resistors and field weakening, depending on what is available in the region the train is used. One of the last trains with this design were the 205 series emu-s, designed just 2 years before the end of the JNR. These trains are still in service and some of them got upgraded to more modern IGBT control systems during the years. The general rule nowdays is anything goes that works, but higher performance modern systems that require less energy are preferred.

[NGT6 1315]

Thanks! Interesting to learn about sources of foreign inspiration, and about modernisation of existing stock being even more common than I had realised.

 

As for power regulation on AC motive power, I suppose the somewhat more complex approach of combining tap changers and secondary side rectifiers would have been justified by being able to use the same types of traction motors across different classes built for all OHLE power systems?

 

And speaking of electric power, do you know what the usual ETS/HEP voltage is (assuming there are nationwide standards)?

[kvp]

 

As for power regulation on AC motive power, I suppose the somewhat more complex approach of combining tap changers and secondary side rectifiers would have been justified by being able to use the same types of traction motors across different classes built for all OHLE power systems?

While some systems were built with rectifiers and even choppers (in europe too), if you use series wound motors, you don't need the rectifiers. These motors will work pretty much with any kind of AC or DC power, since the stators change polarity together with the rotors. This means you don't have to rectify the AC power, just decrease the voltage to the operating voltage of the motors, which is most of the time the standard ovearhead DC voltage. Auxiliary systems might need a rotational converter (motor-dynamo set), but even interior lighting and air compressors can work with both AC and DC as long as voltages and delivered power match. The 25kV AC only series 0 shinkansen was using simple tap changing. This is a very effective way to control a train as there is very little loss, but without rectification, the motors have to be series wound. This technology was used for example in the american GG1 electric locomotive built in 1934. The shinkansen was special that it empolyed a control system commonly found on many pre ww2 commuter emu-s, the classic and simple traction system of a tap changer locomotive and the high voltage line frequency overhead power developed before the war in europe.

 

 

And speaking of electric power, do you know what the usual ETS/HEP voltage is (assuming there are nationwide standards)?

There are no nationwide standards for the private companies, but afaik JNR used 1500V for the trainlines on the 1xx series emu-s as this was what came off the overhead in DC operation and it was easy to get 1500V even from the 20/25kV 50/60 Hz AC lines.

[NGT6 1315]

While some systems were built with rectifiers and even choppers (in europe too), if you use series wound motors, you don't need the rectifiers. These motors will work pretty much with any kind of AC or DC power, since the stators change polarity together with the rotors. This means you don't have to rectify the AC power, just decrease the voltage to the operating voltage of the motors, which is most of the time the standard ovearhead DC voltage. 

 

Knowing common design principles of various traditional German AC electrics, I have been aware of tap changers with on-load assisting thyristor units for smoother power regulation and reduced propensity of wheelslip, but the layout I understood to be present on Japanese AC locos with a full secondary side rectifier beyond the tap changer is a design which was not at all common in German locomotive design.

 

Do you know how many power notches (roughly) were, or are, available on electric motive power from the JNR period?

[kvp]

There were lots of european examples, the oldest one is the hungarian V43 'sily' locomotive series with a transformer, a tap changer, a full bridge silicium rectifier and two huge full bogie DC motors, making it a B-B. Some french and german locos followed it, especially french ones. It's still in service after half a century later, since it's a simple and reliable construction. There were some less successful US mercury rectifier locos earlier.

 

However i would like to point out that most japanese JNR locos did not use a rectifier or thyristor at all. You can find the number of standard speed steps in the Usui pass topic somewhere on the forum. (can't find it atm, but the answer is several dozen)