Automatic Train Protection

A number of tests in connection with the above were carried out at Old Dalby in April and June 1992 and again in May 1993.

Wheelslip is a term used on the railway to describe slipping due to excessive braking but is also applied to wheel spin where traction is lost.

Wheel slip (spin) tests were carried out on the Belgian TBLİ Automatic Train Protection (ATP) system, manufactured by ACEC of Charleroi, which was then being fitted to the power cars operating on the Great Western main line.

It is not generally known but in addition to the 89 HST power cars on GWML the ACEC ATP system was also fitted to two Class 56 locomotives (56033 and 56039)  for further evaluation. (Similarly two Class 47 locomotives were fitted with the German SelCabİ system, manufactured by Alcatel SEL AG of Stuttgart, which was then being fitted to 39 Class 165 DMU's operating on the Chiltern lines out of Marylebone).

Both of the pilot ATP systems rely upon the accurate measurement of the distance travelled along the track. When wheel slip (spin) occurs, it tends to upset the measuring ability of the tachometers and on-board software is used to compensate for this. Sometimes the software fails to compensate correctly resulting in the failure of the system to recognise loops or beacons as they are not where it expects them to be. A number of problems with excessive wheelslip (spin) on the power cars had been experienced during testing and commissioning on GWML. As this was a pressing problem which needed to be resolved since the axle which carried the tachometer was powered and hence subject to wheelslip (spin).

In order to optimise the compensation software settings wheel slip (spin) tests were carried out on the class 56 up the 1 in 200 gradient between Stanton Tunnel and Widmerpool with one bogie isolated.

The method used water-spraying equipment fitted to the locomotive, which wetted the rails in front of the axle carrying the ATP tachometer and this combined with the trailing load, tended to induce wheel slip. Having measured the actual distance run along the track and comparing this with the distance run as calculated by the ATP system (from the tachometer mounted on one of powered axles) the ability or otherwise of the software to adequately compensate for the wheelslip was assessed. If necessary software adjustments could be made and the tests repeated.

Click on the pictures for a bigger image - all pictures are the authors unless otherwise credited

Ready to roll

On 3rd June 1992, class 56 No: 56033 stands in the cutting between Widmerpool and Stanton Tunnel with a train of eight loaded Sea Cow hoppers. It is about to pull away up the 1 in 200 climb towards Folly Hall.


Another view of the train from the cess side

Assessments utilising a seven-car GW HST set with power cars 43016 and 43151 were also conducted at the test track on 18th and 19th May 1993. I believe the only way we managed to get hold of a set was the fact that it was due for its central door locking modification. After the tests it went straight to Landore for the mods to be carried out.


Three ATP-fitted power cars at Paddington in 1992

The principle was similar, water spray equipment fitted to the leading PC and during the tests the trailing power car was shut down  The full set was then hauled up the bank and the effect of the resulting wheel slip assessed. Unfortunately I have no photographs of these tests.

The Class 47's were never subjected to the same tests as the development of the system for variable train lengths was not a priority. As the Class 165's carried their tachometers on trailing (non-powered) axles they did not experience the sort of wheel slip problems of the HST's.

For more information about ATP commissioning on the main line see my train testing pages.

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