SS8 electric locomotives in Hong Kong

Despite both Hong Kong and Mainland China using the same 25 kV AC electrification system for their mainline railways, for many years DF11 diesel locomotives were used to haul the Intercity Through Train that crossed the border.

Diesel locomotive DF11 0009 leads a northbound train into Fo Tan

The reason – the pantographs fitted to China Railways electric locomotives was incompatible with the overhead wires in Hong Kong.

Pair of electric locomotives head between the platforms at Shanghai Railway Station

Chinese-language Wikipedia covers the gory technical details.

China Railways SS8 electric locomotives use TSG3 630/25 single-arm pantographs with metal slide plate and straight bows.This is different from the European standards used by Hong Kong’s Kowloon-Canton Railway Corporation, which requires curved bow heads and a carbon slide plate.

The first modified pantograph was installed and tested in March 1999, with the modified SS8 locomotive used to haul through trains from 1999 to 2002 and 2004, but the KCRC believed that even if the TSG3 pantograph was modified, the risk of damaged to the contact network was still high.

In 2000 the German company of STEMMANN-TECHNIK and Datong Electric Locomotive Plant came to an agreement to use the German DSA150, 200, and 250 series pantograph technology. The Chinese produced DSA150 and DSA200 pantographs adopt European standards, with air springs that absorb high-frequency vibration, and are fitted with carbon slide plates.

In 2005 a DSA series pantograph was fitted to a SS8 electric locomotive, and on 3 January 2008 the first China Railways electric locomotive entered Hong Kong for many years – SS8 0191. By 2009 additional services were hauled by SS8 locomotives, and by 2015 all through trains were now electric hauled.

As of December 2012, SS8 electric locomotives that have entered Hong Kong include: SS8-0141, SS8-0148, SS8-0156, SS8-0163, SS8-0166, SS8-0173, SS8-0181, SS8- 0186, SS8-0191, SS8-0192.

Despite the opening of the Express Rail Link in 2018, SS8 electric locomotives still haul Intercity Through Trains into Hong Kong.

Electric locomotive SS8 0191 hauls a Through Train through Sha Tin station

The ten SS8 locomotives approved for operation into Hong Kong have been fitted with equipment for the Automatic Warning System (AWS) used on the East Rail Line, but are not fitted with equipment to automatically shut off power through neutral sections.

Instead train drivers have to shut off and restart power through neutral sections according to lineside signage, which is of the same design of that used by the Chinese Ministry of Railways, right down to the simplified Chinese characters.


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25 kV AC railway electrification in Hong Kong

Hong Kong MTR uses electric trains, powered by two different technologies – 1500 V DC on the ‘urban’ rail lines, and 25 kV AC for the former KCR network. Today we look at 25 kV AC railway electrification across Hong Kong.

MTR East Rail train passes Shatin to Central Link works at Ho Man Tin

Powering the trains

Each train has a pantograph.

Pantograph on a Metro Cammell EMU

Or maybe many.

Under the noise barrier tunnel at Mong Kok East

To collect power from the overhead wires.

Northbound EMU passing Science Park

Fed by a handful of substations.

Traction substation for the MTR East Rail at Ho Man Tin

Which have transfomers to convert 132 kV power from the CLP Group grid to the 25 kV power used by the railway system.

Traction substation for the MTR East Rail at Ho Man Tin

The substation at Fanling looking very much a product of the KCR in the 1980s.

Google Stret View

While that at Tai Wai looks like any other mosiac tile clad building in Hong Kong.

Google Stret View

Taking a deep dive

A total of six substations provide the 25 kV AC traction power to the MTR network, with fifteen 132 kV to 25 kV transformers between them – ten of which are active and five on standby.

East Rail, four active transformers in three substations:

  • Tai Wai: 1x 38MVA active, 1x 38MVA standby
  • Fanling: 2x 26.5 MVA active, 1x 26.5 MVA standby
  • Ho Man Tin: 1x 26.5 MVA

West Rail, five active transformers in three substations:

  • Ho Man Tin: 1x 26.5 MVA
  • Kwai Fong: 2x 26.5 MVA active, 1x 26.5 MVA standby
  • Tin Shui Wai: 2x 26.5 MVA, 1x 26.5 MVA standby

Ma On Shan Rail, one active transformer:

  • Tai Wai: 1x 38MVA
  • Wu Kai Sha: 1x 38MVA standby

Standby transformers are in place to ensure that if an active transformer fails, train service can be maintained by switching in a standby transformer, restoring the 25 kV AC supply to the overhead wires. Without them, neighbouring transformers can be switched in to supply the section, but the additional electrical load means train services need to be reduced.

Due to the nature of AC power, the power supply from each transformer needs to be separated by neutral section is required to prevent a train from short circuiting the different electrical phases.

On East Rail neutral sections include:

  • Lo Wu, at the connection to the Guangshen railway
  • Fanling, at traction substation
  • Tai Po Kau, at sectioning cabin
  • Tai Wai, at traction substation
  • Ho Man Tin, at traction substation

On West Rail:

  • Tin Shui Wai, at traction substation
  • Ho Pui, at sectioning cabin
  • Kwai Fong, at traction substation
  • Yau Ma Tei, at sectioning cabin

And on Ma On Shan Rail.

  • City One station

On the approach to each neutral section a magnet on the tracks indicates to passing trains to begin coasting through the section, and run onboard systems from battery power, until a second magnet after the section will indicate it is safe to switch back to overhead power.

Clear as mud? Dr. C.T. Tse from the The Hong Kong Polytechnic University included a diagram of the complete network in a presentation titled ‘Tackling Power Quality problems in Railway Systems’.

Presentation by Dr. C.T. Tse

A brief history of 25kV railway electrification in Hong Kong.

  • 1981: Commissioning of Tai Wai KCR substation, the new East Rail Line was supplied by two transformers.
  • 1989: Commissioning of Fanling KCR substation with two transformers. East Rail now supplied by four Tx in two s/s.
  • 2003: Commissioning of Tin Shui Wai West Rail substation, supplying power to the new line.
  • 2003: Commissioning of Kwai Fong West Rail substation, power was then supplied by four Tx in two s/s.
  • 2004: Commissioning of Ho Man Tin KCR substation, transformer HMTN replaced transformer TWS, and TWS was then at standby. ERL power was then supplied by four Tx at three s/s.
  • 2004: East Rail was extended to East Tsim Sha Tsui, power supplied by transformer HMTS. ERL power was then supplied by five Tx in three s/s.
  • 2005: Commissioning of new Ma On Shan Rail, power was supplied by one Tx of MOS.
  • 2009: Kowloon Southern Link was completed and East Tsim Sha Tsui extension became part of West Rail. Since then, West Rail power was supplied by five Tx in three s/s, and East Rail by four Tx in three s/s.

Something incredibly obscure

Dr. C.T. Tse also has a presentation titled Impact of Imbalance due to Single-Phase Traction Load that details the impact that the unbalnaced 25 kV AC traction network places on Hong Kong’s power grid.

AC traction is of single phase, and imbalance to 3-phase supply is inevitable.

To minimize the imbalance, an engineer should evenly shares load to each phase at design stage.

The imbalance for 3 or 3-multiple sections is zero. The imbalance for non-3-multiple sections decreases with more sections.

In AC traction design, the traction load of each line section depends on the line length, number of sections, the train headway (peak or off-peak), the number of cars in each train; all information are ready at design stage.

East Rail is the dominant line in KCR with three times transformer loading to those in other lines.

However since 2004 the East Rail transformers are only connected to two phases, resulting in a current imbalance of 25.5% between the phases.

This is worse than the 25% imbalance in the late 1980s when there were only 4 sections.


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Powering the MTR Light Rail network

The MTR Light Rail system in Hong Kong comprises of 68 stations on 36.2 km of route, served by 150 light rail vehicles. But how are they all powered?

Phase II LRV 1089 on route 507 approaches Siu Lun stop

How it works

The system is electrified using 750V DC overhead wires, like most modern light rail networks.

Overhead wires at Pui To station

Power is supplied by CLP Group via three 132kV / 11kV AC infeed substations – located at Tuen Mun, Yuen Long and Tin Shui Wai.

Google Street View

A network of 11kV AC underground cables then fan out to 16 rectifier stations operated by the MTR.

Rectifier station R2 on the MTR Light Rail

The 11kV / 750V transformers are located outside.

Rectifier station R10 on the MTR Light Rail at Yuen Long

And the rectifier equipment that convert AC power to DC power are inside.

Rectifier station R2 on the MTR Light Rail

Finally, underground cables run to the nearby light rail tracks, where the 750V DC power is fed into the network of overhead.

Traction power feeders at rectifier station R2

Tracking down the rectifier stations

In my time exploring the MTR Light Rail network, I’ve managed to stumble upon a handful of rectifier stations – R2, R3, R6, R7 and R10. So where are the rest?

We start at Tuen Mun Ferry Pier where rectifier station R1 is located in the middle of the reversing loop.

Google Maps

I fount R2 on my own – down a side street at Tsin Shan Tsuen.

Rectifier station R2 on the MTR Light Rail

R3 was an easier find – in the middle of the disused revering loop at On Ting.

Rectifier station R3 on Tuen Mun Heung Sze Wui Road at Siu Lun

R4 is further north at Ho Tin, and co-located with the CLP Group infeed substation.

Google Street View

R5 is out in the open beside the tracks at Shek Pai.

Google Street View

As we head north towards Yuen Long, we find R6 at Siu Hong.

Google Street View

R7 at Chung Uk Tsuen.

Rectifier station R7 at Chung Uk Tsuen

R8 at Tong Fong.

Google Street View

R9 at Shui Pin Wai – the second rectifier station co-located with a CLP Group infeed substation.

Google Street View

And end at R10 at the Yuen Long terminus.

MTR Phase I LRV 1038 on route 615 departs the Yuen Long terminus

R11 is back at the Tuen Mun end of the network, hidden away inside the Light Rail depot.

Google Maps

R12 is on a side street at Hoh Fuk Tong, constructed as part of the eastern Tuen Mun extension in 1992.

Google Street View

And finally we end in Tin Shui Wai – R13 is beside the bike path at Tin Shui, and opened with the northern extension of the network in 1993.

Google Street View

Followed by R14 in 2003 – north of Tin Shui Wai station, and the site of the third CLP Group infeed substation.

Google Street View

R15 at Tin Wing. (once the Tin Shui Wai terminus)

Google Street View

And R16 – located in the middle of the reversing loop at Tin Yat terminus.

Google Street View

So how did I find the rest of the rectifier stations?

I had a little help – the unofficial MTR 365 website has a full track and electrical diagram of the MTR Light Rail system, which combined with an hour or so exploring on Google Maps, got me to where I am now.



I’ve also managed to track down the traction power substations that power the trams and trains of my home city of Melbourne, Australia.

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Driverless baggage tractors at Hong Kong International Airport

December 2019 saw a new kind of vehicle enter service at Hong Kong International Airport – an “Autonomous Electric Tractor”.

Airport Authority Hong Kong photo

The tractor was developed by Beijing-based autonomous driving technology startup Uisee Technology, and is used to transport baggage from Terminal 1 to SkyPier.

With the Airport Authority Hong Kong media release describing the reason for their introduction.

The Autonomous Electric Tractor (AET) at Hong Kong International Airport started operating at Hong Kong International Airport on 30th December 2019. It is the first AET to be put into live operation at an airport anywhere in the world. AET has extended its service area starting from October 2020, running between SkyPier and the Baggage Hall at Terminal 1 to deliver baggage for air-to-sea and sea-to-air passengers.

Steven Yiu, Deputy Director, Service Delivery, Airport Authority Hong Kong, said, “Airport Authority Hong Kong spent more than one and a half years, testing the AET operations at Hong Kong International Airport, to develop it to be more reliable, safer and the operation smoother than traditional tractors. Many traffic accidents are caused by drivers having long working hours and fatigue, as well as poor weather conditions like heavy rain or fog. Hong Kong International Airport has deployed the AET based on the considerations of low labour availability, accidents reduction and efficiency improvement.”

By the first quarter of 2021, all traditional baggage tractors operated manually at SkyPier will be replaced by AET tractors.

And the technology behind it.

There is no driver or passenger in the cabin of AET, but this tractor is running between SkyPier and the Baggage Hall at Terminal 1 at a speed of 20km per hour to deliver baggage for air-to-sea and sea-to-air passengers.

The AET is equipped with a highly accurate dGPS system with a range of error of just 10 to 15cm.

Steven Yiu said, “If anything appears within 10 metres of the AET, it will stop immediately. The response is even faster than a human can react. This is because the AET instantly detects objects and calculates the distance of its surrounding within a range of 10 to 35 metres. The braking system will be triggered if anything detected, and the AET will slow down until it stops within 10 metres of the detected object.”

There are two sets, a total of eight HD cameras mounted on the sides of the AET and three lidar sensors to ensure safety and flexibility.

Further reading

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The evolution of MTR network maps over time

Recently I got an interesting question from a reader – “do you have a photo that shows the MTR network map on a station concourse during the mid-late 1980s”. Unfortunately I didn’t have one on hand, but it led me down an interesting rabbit hole.

The massive list of MTR ticket options detailed at Tung Chung station


The earliest map I found was this one from 1980, showing the completed ‘Modified Initial System’ between Kwun Tong and Chater (now Central).

Scan via Stand News


Next up is this map from 1998, featuring the Tsuen Wan line opened in 1982, the Island line in 1985, and the Kwun Tong line extension in 1989. photo

The same network map appeared on the reverse side of single journey tickets.

@sgcty12 photo

And I found a photo from showing the map in the context of a station concourse. photo


In 1998 the Tung Chung line and Airport Express were added to the network map, following the completion of the Lantau Railway. photo


In 2002 the first stage of the Tseung Kwan O line opened. photo

And today

In the years since the MTR has continued expanding – you can watch the network grow here.

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