Westinghouse Style K Powerframe in Malmö, Sweden

The Westinghouse Brake & Signal Co. Ltd. Style 'K' power frame at Malmö Central was the only Westinghouse frame in Sweden, but it was important as it pioneered the switch from german-style to british-influenced signalling principles in Sweden. Only by taking this step was it possible to control large stations from a single signal-box. It was also an incentive to the swedish Signalbolaget (a subsidiary of  the Ericsson telecom company) to develop an electrically-locked frame.

Until 1925 Malmö Central Station was controlled from several mechanical signalboxes.  The station was rebuilt during the 1920s, and the State Railways wanted to rationalise the signalling and control the whole layout from a single box. This was only possible if shunting could take place on signalled and locked routes. All previous interlockings in Sweden were of german types, where trains run on locked routes, but shunting is regulated by hand-signals.  Track circuits were uncommon. At all but the smallest stations several boxes where necessary to control the layout. These boxes were under the control of a local controller (train director) using electrical releases for the signal levers.

In british-style interlockings it is customary for shunting operations to be directed by fixed signals on locked routes, so the State Railways decided to buy a Style K frame from the british Westinghouse Brake & Saxby Signal Co.  The Swedish Signalbolaget (signalling subsidiary of the Ericsson telecom company) acted as an intermediary.

 The powerbox was brought into use in 1925.  The picture shows the box in 1965  [Göteborgs Landsarkiv]

Exteriörbild stlvhuset

Interiörbild 1929
The picture above, from 1925 - 1933,  shows the frame and the illuminated diagram.  [Swedish Railway Museum, picture number 6081].  

The signal levers were of the push-pull-type. The lever could control two routes, as the signalman could either push or pull the lever from the neutral position. The annotation for the routes accordingly used the suffix psh for push and pll for pull.  

Ställverksapparaten snett bakifrån
This picture, probably from the 1970s or 1980s, shows a variety of telecommunications equipment. [Swedish Railway Museum, picture number 6082].  

Technical description

This description is based on data in Banavdelningens berättelse (State Railway infrastructure department's annual report)1925 pp 102 -

The frame was equipped with

A small installation compared to the style K frame at London Bridge (311 levers)!

There were 57 track circuits. 77 main routes and 186 shunting routes could be set up. The interlocking used 98 AC relays and 173 DC relays.

Power supply:


The diagram reproduced below is from Banavdelningens berättelse 1925, page 105.  The all-over roof covering the main platforms is  near the left edge. Platform tracks VIII to XII belong to the so called Local Station, used by short-distance trains. The 'box is near the upper edge.

The double-tracked Southern Mainline to Stockholm leaves to the right. Connecting tracks to the freight yard are brought over the mainline on a viaduct.  The two tracks disappearing near the lower right corner of the diagram are the so called Contintental Line to Trelleborg and the track to the State Railway's rolling stock works.  Breaks in the track on the diagram are used where the actual distance is considerably longer than shown.

The home signals are fixed to a gantry (Signalbro) spanning most of the lines. A single green light is shown for routes to the short tracks of the Local Station. Routes to the longer platform tracks number  I - VII are signalled by two green lights. This was contrary to later practice.

Inner starting signals could be found near the ends of most platforms. These signals co-acted with repeater signals on the outer edge of the all-over roof. Outer starting signals were mounted on the same gantry as the home signals.

Shunting routes where signalled by position-light dwarf signals.

"Blockpost A" and "Blockpost B" are automatic block signals for the Southern Mainline.  Automatic block was necessary as, due to the distance,  the signalmen could not observe the tail lights of all trains.
Schematisk bangårdsritning med signaler mm

Signaler och rysk sovvagn
This picture, from february 1980, shows some of the inner starting signals and a few position-light dwarf signals.  The Southern Mainline was only electrified during the 1930s, so no overhead line portals were available for mounting  the signals when the power interlocking was built.  The coach visible behind the locomotive of the departing train is a sleeper bound for Moscow via Trelleborg - Berlin.

The Malmö interlocking used main signals as inner starting signals (intermediate signals in current swedish terminology). This use of main signals was standard practice in earlier mechanical and power interlockings. However, most power interlockings built subsequently used only  dwarfs as inner starters. These dwarfs can show a green aspect to indicate that a main route has been set up. Shunting routes are always indicated by lunar-white lights only.  Nowadays, as a safeguard against trains passing signals at danger, dwarf signals for main routes display a red aspect at all times except when a main route has been set up.

Levers and Indicators

Detaljbild med ställare och spegelfält
Above each lever can be seen a plate with the number of the lever  and, in the case of a signal lever,  a list of other levers which are required for the route. Signal indications are repeated on the illuminated diagram. Free track circuits are indicated by a white light.  Originally, contrary to later practice, the track circuit lights where normally extinguished, and lit up to indicate occupation of the track circuit. Switch position indicators can be seen immediately above the switch levers. These indicators were also known as windmills. Above some of the signal levers are time releases used for instance if it is necessary to cancel a main route after the signal has been taken off.   Picture No 6086,  Swedish Railway Museum. This picture was probably shot after 1956 - the clocks on both sides of the ammeter are non-existant on the picture taken by  J.R. Batts in 1956..  

Interiörbild med personal och ställare
A picture from 1963 [via SJ fotoklubb, now in Göteborgs Landsarkiv]

Interiör med två ställverksvakter
This picture is probably from 1965, and was reproduced by the Malmö Railwaymen's Photo Club.

Illuminerad spårplan och strömförsörjningstavla
Illuminated diagram and controls and indications for the power supply. [SJ fotoklubb Malmö, Göteborgs Landsarkiv]

Detaljbild ställare och spegelfält

Left: Enlargement of part of a picture from the swedish Railway Museum.   A lever collar has been placed on one of the levers so that it can not  be thrown by the signalmen

Right: A few pieces from the frame have been preserved at the infrastructure authority's museum at Ängelholm. The indicators are not in the same position as on the real frame. The small box in the upper right corner is for emergency release of a main route. This arrangement was  replaced by time releases at an unknown date    [2005]
Ställare på banmuséet

Local control.  Safety and Reliability. 

At interlockings built prior to the Malmö powerbox, the work of the signalmen was controlled by a local controller (train director, sw tågklarerare) using electrical releases. This was neccessary to coordinate the boxes, and as a safety measure due to the lack of track circuits.  In  the Malmö powerbox,  locking and track circuits made it possible for the signalmen to operate the interlocking plant with complete safety without releases from the controller.  The local controller's office, near track VII, had a simplified illuminated diagram to show track occupancy  on some platform tracks, but no releases for the signals.  The local controller gave the right away handsignal to departing trains,  but the signalmen mainly managed the train and shunting movements on their own.   This partition of work was applied also to most later large powerframes in Sweden. 

A few weeks after the interlocking had been brought into use,  the last car of an arriving train was derailed and overturned when a switch was thrown under the train. A guard was killed and some passengers were injured. The cause of the accident was a faulty part in the locking frame. Otherwise, the interlocking plant seems to have functioned well.  

Relock or Replace the Powerframe?

In the middle of the 1950s, it was time again for rebuilding Malmö Central station. The State Railways 3d district launched the idea that the  powerframe ought to be replaced by a relay interlocking. Slackness had developed in the locking. As this was the only British-style frame in Sweden, it was thought that maintenance could be simplified if it was substituted by standard equipment. In a perhaps somewhat exaggerated report, the district stated that the interlocking would have to be taken out of use for six months if it was decided to relock and extend the Styel K frame. During these six months hand signalling was to be used.

On the 19th September 1956 Westinghouse Brake &Signal Company  offered
Delivery would be possible 9 - 15 months after the order was placed. The installation of the new equipment could be carried out by four locking fitters during a 12 hours posession after preparatory work during several nights. Alternatively, four locking fitters could accomplish the entire relocking and extension during three weeks with disconnected locking and handsignalling.

Westinghouse mentioned that they considered the locking fitters of the State Railways to be thoroughly conversant with the locking of the Style K frame, and capable of carrying out the relocking and extension.  

The state railways decided to relock and life-extend the powerframe. This decision was probably influenced by a lack of suitable swedish relay interlocking technology for large installations.

I have not as yet managed to get information on how the relocking was carried out and how long handsignalling had to be used. 

Ställverksapparat, ställverksvakt och lokalställare
 Above: Probably a picture from the final decade of the box. At the window can be seen equipment possibly used to control a switch machine which for some reason was not on the frame. [Swedish Railway Museum, Picture No.6080]    
Below; Picture in Göteborgs Landsarkiv, via SJ fotoklubb Malmö
Lokalställarlåda och ställverksvakter

The Style K frame was the most technically advanced frame with mechanical locking in Sweden.  It was also the last really big swedish powerframe with mechanical interlocking. In 1926 or 1927 the first electrically interlocked frame was brought into use at Hässleholm. This development was parallell to Westinghouse's development of the Style L frame. The Style K frame in Malmö was replaced by a computer based interlocking in 1982.

More pictures from Malmö can be found at John Hinson's site

More information on Style K powerframes can be found at Mark Adlington's website.


Documents from the State Railways in Riksarkivet (public record office)
Banavdelningens berättelse 1925

Pictures in the archive of the Swedish Railway Museum, Gävle, and Göteborgs Landsarkiv.

Swedish Version


Last updated 4 Februari 2006