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Retrofit of the Cologne tram 2400 series

The Cologne Public Transport Authority looks to the BENNING Electrical Machines department as an expert partner for long-term mobility.

A study carried out in August 2015 states that Cologne is the German city of traffic jams. Last year alone, motorists spent around 65 hours in their cars there, thwarted by road closures or works in the city centre and its motorway ring. This makes it all the more important for residents and commuters in the cathedral city to have recourse to the Cologne tram. With its 11 lines and 195 km long railway network, it is the backbone of public transport. But to be able to continue to ensure all passengers a safe and smooth ride in the coming decades, extensive renovation and modernization measures are required.

The tram 2400 series prototype in a factory building of Cologne's transport service
The tram 2400 series prototype in a factory building of Cologne's transport service

“Umbau 2100er Stadtbahnwagen” (Retrofit 2100 light rail vehicles) is the name of the Cologne Public Transport Authority’s retrofit project which began three years ago. The plan is for all 28 cars of the tram K2100 series – also known as B-Wagen – to be completely renovated by 2017, thus extending the life expectancy of the 30-year-old high-floor cars by another three decades. An objective that theoretically could also have been met by rebuilding the light rail vehicles from scratch – though a detailed review of all elements led to the conclusion that a repair not only makes sense, but also brings two key advantages: on the one hand, the tried and tested methods of engineering can be adhered to, thanks to which, in the past, failure-free and trouble-free continuous operation was always guaranteed. An example of this is the driving-braking control system developed in the 1960s for the previous model. On the other hand, restoring the 2100 car also proves relatively economical. Approx. 3.2 million would need to be raised to purchase a single car, so these costs are now halved.

A set of repaired  rail engine anchor
A set of repaired rail engine anchor

As part of the modernisation drive, the cars have to be completely gutted, leaving only the bare metal, consisting of the chassis and the bogie pivots and motors. All components have to be very precisely evaluated and either refurbished or replaced – a task which, as well as a large amount of time, also requires expert knowledge, especially when it comes to making the central control elements, bogie pivots and motors also function for as long as possible.

Specialist knowledge required

As the K2100 series rail vehicles built in the 1980s were not built for just five or ten years, but for a minimum of 30 years, they still have DC motor drives. However, the general level of knowledge about these is rapidly declining because AC motors are now almost exclusively used in the railway sector. With experience in repairing AC as well as DC motors, BENNING serves as an important expert partner to the Cologne Public Transport Authority, and has a decisive role in ensuring that the railway cars are kept mobile and that soon their age will no longer be an issue.

Competent partner for long-term mobility

In the BENNING Electrical Machines department, which deals with rotating machines, it was recognised many years ago that traction is an interesting area of responsibility both technically and economically. After the system provider decided to no longer use DC motors in traction, BENNING has invested precisely in this area. Most familiar with the repair of traction drives, several BENNING employees initially took antiquated tram traction motors, which were exclusively DC motors, to the Werk II factory in Bocholt. With the technical equipment available there, it was possible to make all drive motors – whether AC or DC motors – as good as new. Even where there was major damage, it was possible to restore or even implement improvements in performance and efficiency without major problems.

In the background, the old 2100 tram, and in the front the Cologne Transport Authority's new 2400 tram series
In the background, the old 2100 tram, and in the front the Cologne Transport Authority's new 2400 tram series
TIG welding on a commutator
TIG welding on a commutator

Extensive repair work

If a DC motor is brought to the BENNING factory for a retrofit, it will be thoroughly examined. This is a sophisticated but also very important part of the repair process, which is also summarised under the generic term of diagnostics. BENNING dedicates a great deal of attention to diagnosis as this will act as a basis for further decisions, to achieve a high life expectancy of the motors. This includes both the dismantling and cleaning, and the conservation of components in order to be able to create a comprehensive inspection report. The report contains all relevant mechanical and electrical readings and is available to customers for their information or consultation, thus creating transparency from the outset.

Rotor and stator packets are inductively heated and analysed for damage with a thermal imaging camera. If the thermography report presents temperature differences of more than 10 degrees, this will be mentioned in a subsequent meeting with the customer. If the delta amounts to more than 20 degrees, the laminated core will definitely need to be replaced in order to prevent future damage caused by hot spots. The renovation of the laminated core begins with the precise cutting of rotor and stator packets. In order to ensure the usual high level of quality, precision and degree of freedom here, this operation is performed at the company’s own punching centre – always with an eye for the finest detail.
When rewinding the rotor and stator, the most suitable materials are also used in order to guarantee a long service life and to counteract adverse weather conditions in winter, for instance. To achieve an optimum result, on the one hand, the connection of rotor winding and commutator takes place in the TIG welding process. On the other hand, the winding insulation of copper always consists of Kapton, which has a higher temperature resistance than the required insulation class “H” (180 °C). Impregnation is done in a vacuum process.

Thermographic image
Thermographic image

Create conditions for approval

The first nearly finished prototype of refurbished light rail vehicles came out of the workshop hall as early as November 2012 to undergo extensive quality tests performed by the Cologne Public Transport Authority. It was particularly important to test the braking capability and to find out if other vehicles could easily be hitched or towed.

Currently, the complete quality control documentary file not only contains the findings report and thermography report, but also the commutator diagram, a balancing test, an armature test report and documentation relating to the function of the stator and motor. These data are not only important to be able to demonstrate the individual steps of testing to the Cologne Public Transport Authority; they also represent a significant constituent part for approval by the regulatory authority. To this end, all conditions are created so the light rail vehicles of the K2400 series can guarantee safe and smooth operation in the cathedral city over the next 30.

Further information

contact: Johannes Dyhringer
telephone: +49 (0) 2871 / 93 - 427

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