INTRO: Professor Satoru Sone of Kogakuin University examines the possibility of using compact power electronics to create a fully double-deck trainset within the constraints of a tight loading gauge

IN HIS ARTICLE on the development of double-deck power cars (RG 2.01 p107), John Dunn refers to the difficulty of accommodating traction and auxiliary power equipment in the roof of EMUs operating on Japan’s classic 1067mm gauge network. As he points out, it has up to now been necessary to use the space on the lower deck of the power cars to house equipment.

This raises the interesting question as to whether recent developments in power electronics now make it possible to construct fully double-decked EMU sets for Japan’s narrow gauge without sacrificing passenger space, even on the power cars.

The problem lies with the loading gauge, which is restricted by the maximum height permitted through some of the older tunnels. Many of these tunnels are single track, and they impose a rounded profile on the roof.

Series 215

Both the JR Group and private commuter lines such as Kinki Nippon Railway (Kintetsu) and Odakyu Electric Railway have built double-deck EMUs in an attempt to increase capacity. A good example is Series 215, the first version of this 10-car trainset having been placed in service by JR East in 1992. The objective was to provide a guaranteed seat to long distance commuters paying a small extra charge.

The maximum possible height above rail over the centre of the track is only 4070mm, and because of the curved roof profile, the height of the pantograph in the lowered position must be no more than 3970mm.

Thanks to the narrow gauge, the back-to-back distance between the wheels that is available for the traction motors is only 990mm. Japanese stations have high platforms, as in Britain, so the vestibule floor height is around 1200mm.

Given this overall height constraint, there is no space above the ceilings of the upper and lower saloons for anything more than thin light fittings, so all equipment had to be located on single-deck parts of the train.

A Series 215 trainset has 1010 seats, which is about 60% more than a similar formation of single-deck cars. As originally built, this EMU used conventional rheostatic control of power supplied for traction, with additional field excitation. Bulky and heavy equipment on the end driving motor cars was located in the space that would have been occupied by a lower deck saloon.

The only exceptions were air-conditioning modules and the pantograph, which have been placed in the roof space above the vestibules and outer ends of the car.

Table I shows where the equipment is located on the end cars, and on intermediate cars that are fully double-deck. Cars 1, 2, 9 and 10 each have four motored axles, with cars 2 and 9 supplied with traction power from cars 1 and 10. Even with rheostatic control, there is ample space on these cars beneath the upper saloon, thanks to the use of regenerative braking which avoids the need for large resistance banks and associated cooling plant.

Space-saving power electronics

Compared to the original Series 215, power electronics allows much heavy and bulky equipment to be dispensed with in more modern versions of this train. The list includes rheostats, switchgear, the field excitation source and its controller. In principle, power electronics are loss-less so there is little heat to be removed.

In the early years of power electronics, however, auxiliary circuits included turn-off circuits (using another thyristor with its capacitor and inductor), snubber circuits to ensure a safe turn-off, gate circuits generating a relatively large current to turn off GTO devices, and smoothing circuits to compensate for slow switching.

Once insulated gate bipolar transistors of sufficient power became available, most of these additional circuits or devices were no longer needed. The only bulky device left in the main traction circuit is the input filter reactor.

Consider a traction inverter supplying four traction motors of around 200 kW each. Using six 4·5 kV 2kA GTO devices with evaporation cooling weighing over 2 tonnes, the volume required would exceed 4m3. In contrast, the modern equivalent uses six 3·3 kV 1·2kA air-cooled IPMs; the volume is less than 0·8m3 and the weight under 500 kg. Thus the volume has been reduced by more than 80%.

In the opinion of an expert designer working for Mitsubishi Electric, ’as far as the traction system is concerned, fully double-decked EMU cars can easily be designed using the experience of Tangara commuter trains operating in Sydney, even if the more restricted space available in narrow gauge trains such as Series 215 is given.’

The original Tangara fleet, built in the late 1980s, was controlled by four-quadrant choppers. Inverter-controlled cars to the same specification were added to the fleet in 1995.

High-voltage AC more difficult

The two standard voltages found on Japan’s national narrow gauge network are 1·5 kV DC and 20 kV 50or 60Hz. Up to now, double-deck EMUs have only been used on DC lines where the voltage favours compact equipment. A little more space would be needed for electrical clearance on 3 kV lines, along with more semiconductor devices to cope with the higher voltage.

Compared to medium voltage DC, high voltage AC is far more difficult to accommodate on a fully double-deck EMU, mainly because of the heavy and bulky transformer. Low frequencies, such as 16 2/3 Hz make the transformer even heavier.

Such a high voltage transformer cannot easily be designed in a thin package for roof-mounting, nor can it be divided into several pieces. If the space between the bogies is occupied by a lower-deck saloon, then the transformer can only be located on the floor above a bogie. Assuming 860mm wheels, this floor will be 1050 to 1070mm high, and it would just be possible to fit a 950mm high transformer into the space below the floor of an upper deck, assuming this extended over the bogie.

High level gangways between coaches (Fig 3a) are popular in Europe and North America, and there is also one example in Japan. Odakyu’s Series 20000 cars are used for limited express trains, which means the number of entrance vestibules can be reduced.

On the Karlsruhe and Saarbrücken trams, which operate on DB tracks at 15 kV 16 2/3 Hz as well as at 750V DC on the city streets, the main transformer is located beneath the floor of the centre (high-floor) section of the articulated vehicles.

Another bulky device is air-conditioning, both the volume and the mass being determined by the prevailing climate, the extent to which the trains are liable to become heavily loaded, and the frequency of stops where chilled air is lost through open doors. Fortunately, very thin roof mounted air-conditioning packages have been developed for metro trains with small profile tunnels.

Other bulky devices necessary on an EMU are the main circuit breaker and air compressor. A height of 550mm is already adequate to house these, and 450mm is thought to be possible in the future.

Articulation benefits

Articulation reduces the number of bogies for a given train, and therefore the total mass, while increasing the proportion of the total length that can be double-deck.

In a practical design for 20m long independently mounted car bodies, the space between the bogies is about 14m and the lower saloon is about 10m long.

Provided the axleload can be increased, as is usually the case with EMUs, an articulated trainset 200m long can have bogies at 14m centres, so the number of bogies for a given length of passenger accommodation is only 73%. There is one fewer bogie per intermediate vehicle, but constraints on axleload, throw on curves and overall train length would result in an articulated trainset having a greater number of shorter bodies (14 cars of 13·6 m versus 10 of 20 m).

At the same time, articulation will cut the single-deck proportion of total length to 41%. Given that equipment must be located in or over the single-deck portions, this 41% seems very critical if high capacity air-conditioning is required (Fig 3b). However, some equipment can be housed under seats, as is done in London Underground tube stock and low-floor LRVs.


The development of power electronics technology has advanced to the point where there should be no difficulty in building an all double-deck EMU for Japan’s narrow gauge 1·5 kV DC lines. For AC lines, when coupled with a requirement for high power air-conditioning, difficulties remain but it still looks possible.

When it comes to high speed inter-city services, we already have the TGV-2N double-deck articulated train in service on AC and DC lines, but with what amounts to a locomotive at each end. It cannot be converted readily into a fully double-deck EMU formation.

But the application of this concept to something like JR East’s E4 all-double-deck shinkansen trainset raises very interesting possibilities, since the benefits of distributed power that permit electric braking are now widely recognised.

Table I. Location of major equipment on Series 215 EMUs

TABLE: Car Type Position Apparatus

1, 10 driving motor underfloor main circuit devices (circuit breaker, controller, field exciter, resistor, switchgear), auxiliary power source, air compressor

lower deck air reservoir, air filter, battery

small room ATP device, brake controller, ground device, low voltage relay

on roof * pantograph, arrester, air-conditioning units

2, 9 non-driving small room air reservoir, brake controller, monitoring device motor over roof * air-conditioning units

3, 5, 8 trailer small room water tank, air reservoir, brake controller,

monitoring device

over roof * air-conditioning units

4, 6, 7 trailer small room air reservoir, brake controller, monitoring device

over roof * air-conditioning units

* above roof of single-deck sections at vehicle ends

Table II. Comparison in size and mass of traction

inverter equipment using different technologies

TABLE: Type conventional GTO IGBT IPM latest IPM

Input voltage kV DC 1·5 1·5 1·5 1·5

Number of motors per inverter 4 1 1 4

Number of inverters per box 1 4 4 1

Motor power kW 165 205 220 200

Output levels 2 3 3 2

Power semiconductors GTO IGBT IPM IPM

Voltage kV 4·5 1·7 2·0 3·3

Current A 2000 400 600 1200

Cooling evaporation heat pipe heat pipe running air cooled dry panel

Number of devices 6 48 48 6

Height of equipment module mm 720 720 650 650

Width mm 2060 1490 600 550

Length mm 3000 3200 3000 2200

Volume m3 4·5 3·43 1·7 0·79

Area m2 6·18 4·77 1·80 1·21

Mass of apparatus kg 2·15 1·95 0·83 0·456

Source: Mitsubishi Electric Corp

CAPTION: JR-East’s Series 215 EMU has 1 010 seats in a 10-car all-double-deck formation. Traction equipment is shared between cars 1, 2, 9 and 10

CAPTION: The upper deck of the Series 215 has a low and sharply curved roof line

CAPTION: Keihan Electric Railway’s Series 8800 EMU trailer car (above left and Fig 1) is one of the smallest double-deck vehicles operating in Japan. However, the cars run in Series 8000 EMUs (left) with conventional single-deck power cars

CAPTION: Fig 3. a) High-level gangways release more useable space for equipment than the classic over-roof position above the bogies.

b) Articulation can increase the amount of space in the body that is available for passenger use, but at the cost of less equipment space

CAPTION: Fig 2. JREast’s Series E4 double-deck shinkansen trainset includes an intermediate car carrying the main transformer and traction converter in end compartments

Are double-deck EMU power cars possible on Japan’s 1067mm gauge?

Professor Satoru Sone of Kogakuin University examines the possibility of using compact power electronics to create a fully double-deck trainset within the constraints of a tight loading gauge. The reduction in size and weight of traction control equipment may enable the development of articulated trainsets, but high-voltage AC applications are likely to prove more difficult, especially where low-frequency supplies require a bulky transformer

Des voitures à deux niveaux sur la voie japonaise de 1067mm, est-ce possible?

Le Professeur Satoru Sone de l’Université de Kogakuin étudie la possibilité d’utiliser des équipements électroniques compacts afin de créer une rame complète à deux niveaux malgré les contraintes dimensionnelles d’un gabarit de chargement restrictif. La réduction des dimensions et du poids des équipements de traction peut rendre faisable le développement de rames articulées, mais la tension élevée d’applications à courant alternatif risque de rendre l’opération plus difficile, plus spécialement lorsque les alimentations à basses fréquences nécessitent un volumineux transformateur

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