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When Dublin had too many tram stops... New AC Motors and Pumps for the fleet

When a tram stops at a tram stop, that’s good. When it stops anywhere else, because it’s broken down, that’s not so good. It not only blocks and disrupts the whole tram network, but in the case of Dublin’s Luas Light Rail system, it also puts the operator at risk of a fine. Transdev – operator of Dublin’s network – asked ERIKS Dublin to get on board and help. 

Passing Tram in a City Centre Decorated for Christmas at Night. Dublin, Iraland
Passing Tram in a City Centre Decorated for Christmas at Night. Dublin, Iraland

The trams in question are first-generation models which have been operating since 2006. Unfortunately, soon after their introduction, it became clear that the brushed DC motor and pump assembly, which controls the flow of Glycol coolant to the tram’s main traction motor, was insufficiently reliable. And when this motor control unit fails, the tram shuts down until the fault is rectified.

This caused problems for many years, with motor commutators continually needing repairs, and motor brushes and bearings needing frequent replacement. The pump was also an issue, as it was custom-designed and by 2020 no longer available.

When the pandemic hit, a 75% reduction in passengers per tram was imposed to enable social distancing. 

This meant there was an urgent need to run more trams. But with frequent breakdowns, extensive downtime for maintenance and long lead times for spares, more trams were often simply not available.

It was a perfect storm for the operator, the tram network, and the passengers patiently waiting by the roadside. Clearly, according to anyone’s timetable, it was time to do 

A Dublin Tram waiting outside Connolly Rail Station
worn gearbox needing an overhaul

DC or not DC? That is the question

Transdev needed to find a replacement DC motor for the Luas Light Rail system trams. ERIKS Application Engineer, Tony Summersby, identified two possible options: one brushless and one brushed. 

A replacement pump from KSB – an ERIKS pump supply partner – was also sourced, matching the existing pump specification and performance, but with a standard rather than custom-designed product. EPDM hoses and ancillary spares were the final pieces placed in the jigsaw. 

Initial tests proved disappointing. Both motors successfully operated the pump, but there were noise problems which – as the MCUs are roof-mounted – meant an unpleasant ride for the passengers. In addition, there were problems with fluctuations in hydraulic performance.

But sometimes motors are just like trams. When you want one, three come along at once.

ERIKS proposed replacing the existing 24V DC motor with a third option: a 400V 3-phase AC motor and pump assembly. This would also require a new DC to AC power supply to the MCU, as most of the trams’ electrical systems operate on 24V DC.

Essential travel

The tram network is essential to travel in and around Dublin. Finding the ideal motor was essential to Transdev. So ERIKS Pump Specialist, Geoff Mason was given special exemption for essential travel to Ireland during the Covid restrictions. This meant he was on hand to help with more trials of the DC motors and the AC option, at Transdev’s Maintenance and Operations Depot in Dublin.

By the end of the trials it was clear that the AC pump / motor option was the most successful solution – providing constant hydraulic performance with negligible noise and low power consumption.

The next step, in late 2020, was the installation of the AC option on 5 Luas trams. These have now completed over 70,000km of trouble-free operation. Meanwhile, ERIKS has upgraded 15 more MCUs to the AC motor and pump assembly.

Room for more benefits inside

The increased reliability of the MCU means less downtime, fewer repairs, and more trams in operation more of the time. Which means more happy passengers and fewer fines for Transdev. But that’s not all.

By standardising the AC motor and pump, ERIKS has reduced the lead time for both the assembly and spares. By eliminating the brushes and commutator required with a DC motor, there’s less maintenance. 

Tram DC/AC Motor Testing
New Gearbox arrangement Fenner P Series

And what was once supplied in three separate parts now comes as a single assembly – reducing the number of suppliers and minimising potential supply chain issues.

Not surprisingly, Transdev has requested conversion of the entire Luas fleet of 44 trams to the AC solution. So now when a tram stops it will only be because someone wants to get on or off. 

For more information on Power Transmission solutions and to get in touch with one of our ERIKS Pump Specialists or Application Engineers, please contact your local ERIKS Service Centre, who will be happy to discuss your options.


#ERIKS #ERIKSIreland #LetsMakeIndustryWorkBetter #Dublin #Transport #Trams  #Engineering

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