Would Batteries Help Voltage Change-over In A Dual Voltage Train Or Tram-Train?
Battery Power And Tram-Trains
Consider.
- The Class 399 tram-trains in Sheffield can work on both 25 KVAC and 750 VDC overhead electrification.
- Their German cousins in Karlsruhe can work on both 15 KVAC and 750 VDC overhead electrification.
In Karlsruhe, there is a ceramic rod between the two overhead cables with different voltages and the pantograph rides across. I suspect that clever power electronics on the tram-train measures the voltage and converts it automatically to that needed to power the tram-train.
I haven’t been able to see how Sheffield connects the two different voltages, but I wouldn’t be surprised if a similar system with a ceramic rod is used.
Look at this picture, I took of a Class 399 tram-train in Sheffield.
Note the BATTERY CHARGE socket to the left of the car number.
Why would an electrically-powered vehicle need a battery?
I suppose it could be to start up the tram-train in the morning and raise the pantograph.
But could it also be for emergency power, to move the tram-train short distances, such as in depots or to assist the vehicle through the dead sections, where the power supply changes from one voltage to another?
The Class 399 tram-trains ordered for the South Wales Metro will also have to cope with discontinuous electrification. So is the technology needed for this already installed in the tram-trains in Sheffield?
Battery Power And Dual Voltage Trains
Suppose you have a train like a Class 378 or Class 700 train, that can run on both 25 KVAC overhead and 750 VDC third-rail electrification.
Third-rail trains with contact shoes deal with discontinuous electrification all the time.
If a dual-voltage train had a battery that could take it say two hundred metres, then I believe that voltage changeover could be simplified and speeded up.
I have watched Class 717 trains change voltage at Drayton Park station and what changes would a limited battery capability make.
The third-rail electrification would stop several metres short of the station and would be removed in the station itself.
Going towards Moorgate, this would be the procedure.
- The train would stop in the station as it does now.
- The driver would drop the pantograph, whilst passengers unloaded and loaded.
- The driver would close the doors.
- The train would accelerate away on battery power.
- After a few metres the train would contact the third-rail and the train’s computer would change from battery to third-rail power.
Going away from Moorgate, this would be the procedure.
- The train would automatically disconnect from third-rail power, where that stopped to the South of the station.
- The train would automatically switch to battery power.
- The train would stop in the station as it does now.
- The driver would raise the pantograph, whilst passengers unloaded and loaded.
- The driver would close the doors.
- The train would accelerate away on overhead power.
The stops should be no longer, than a normal station stop without power changeover.
Conclusion
Batteries may well reduce the time taken to change voltage
In fact, all the electrification from Sheffield-Rotherham-Parkgate is at the same voltage. The overhead equipment can be converted to main line 25kV at a later stage, but at the moment, it’s all at tram voltage.
Just before the tram-trains from Sheffield reach the junction with Network Rail at Tinsley N Jn, there’s a short neutral section, which the tram-trains coast through at ~10mph.
Comment by EWD | June 9, 2019 |
Karlsruhe use a ceramic rod to guide the pantograph between 750 VDC and 15 KVAC.
Is that used in Sheffield?
Comment by AnonW | June 9, 2019 |