The Anonymous Widower

Ride Quality In Class 345 And Class 710 Trains Compared

Yesterday, I had rides in two different Bombadier Aventras.

Both have a smooth ride, that we come to expect from modern trains.

But my bottom was telling me, that the ride on the Class 710 train was smoother.

I have read somewhere, that the train control system on the Class 345 train is a version of the MITRAC system used on many of Bombardier’s earlier trains and trams, which was certainly used on Class 379 trains.

As has been widely reported, Bombardier are introducing a new Train Management and Control System on the Class 710 trains.

They have also had a lot of trouble getting it to work properly.

If I am right about the ride being smoother, could it be that the new TMCS, has much better control of the traction motors and their power supply?

In The Formation Of A Class 710 Train, I stated that the formation of a Class 710 train is as follows.

DMS+PMS(W)+MS1+DMS

Note that all cars have motors, which must increase the smoothness of acceleration and braking.

But then Class 345 trains have lots of motors too!

In this article in Global Rail News from 2011, which is entitled Bombardier’s AVENTRA – A new era in train performance, gives some details of the Aventra’s electrical systems. This is said.

AVENTRA can run on both 25kV AC and 750V DC power – the high-efficiency transformers being another area where a heavier component was chosen because, in the long term, it’s cheaper to run. Pairs of cars will run off a common power bus with a converter on one car powering both. The other car can be fitted with power storage devices such as super-capacitors or Lithium-ion batteries if required. The intention is that every car will be powered although trailer cars will be available.

Unlike today’s commuter trains, AVENTRA will also shut down fully at night. It will be ‘woken up’ by remote control before the driver arrives for the first shift

This was published over eight years ago, so I suspect Bombardier have refined the concept.

Note this phrase.

The other car can be fitted with power storage devices such as super-capacitors or Lithium-ion batteries if required.

Could the Class 710 train be the first Aventra to take advantage of energy storage devices to provide a smoother power supply to traction motors?

The trains could be serial hybrids, like London’s Routemaster buses.

In a serial hybrid vehicle, the following happens.

  • The power supply charges the energy storage device.
  • The energy storage device provides power to the traction motors
  • On braking, the traction motors use regenerative braking and the electricity generated is stored in the energy storage device.
  • Power to provide services for the train comes from the energy storage device.

It is a very efficient system, which also has other advantages.

  • The train can move for a short distance without external power.
  • When the power supply is diesel, it doesn’t need to be run in sensitive areas, like stations.
  • Depots and sidings don’t need to be electrified, which increases safety.
  • As the extract said earlier, trains can have a remote wake-up capability.

The energy storage device between the power source and the traction system would have the effect of smoothing power fluctuations in the supply.

Energy storage devices also have a very low impedance.

  • When the driver asks for maximum power, the energy storage devices can give all they’ve got immediately.
  • When the driver applies the brakes, if they’ve got space, the energy storage devices, will lap it up the energy like a pack of thirsty hounds.

I have no proof, that Class 710 trains are serial hybrid trains, but I think there’s more than a good chance they are.

The trains run very smoothly, with good acceleration and smooth braking.

Perhaps, because the Class 345 trains were designed and built earlier, they had to use the less sophisticated MITRAC control system.

What Size Is The Energy Storage Device On A Class 710 Train?

In What Is The Kinetic Energy Of A Class 710 Train?, I calculated the energy of a Class 710 train.

I calculated the figures for a train with 700 passengers, each weighing 90 Kg for different speeds.

  • 90 mph – 49.4 kWh – Operating speed of a Crossrail Class 345 train.
  • 100 mph – 61.3 kWh – Operating speed of many electric multiple units.

Note that the amount of energy is proportional to the square of the speed.

As the energy storage device must be able to capture all of the braking energy if a train is trundling around North London, I would suspect that two fifty kWh batteries would be more than enough!

But a good control algorithm might cut this considerably!

A total of 100 kWh, would certainly be possible to put under a train, and could be a mix of the following.

  • Fast response supercapacitors.
  • High capacity lithium ion batteries or similar.

This is not an unknown combination on a battery-electric train or tram.

Conclusion

Supercapacitors could be the reason for the perceived smoother ride.

But don’t trust my nearly seventy-two year-old bottom!

Go and experience the trains for yourself and then post your thoughts here!

 

 

 

 

 

July 3, 2019 - Posted by | Transport | , , ,

2 Comments »

  1. Unless the train is operating on ATO there will likely be some dependency on the expertise of the driver.

    Comment by Kevin Roche | July 4, 2019 | Reply

    • I would agree with that. But the 710s are very steady at 75 mph. A bit like one of London’s new battery taxis.

      Comment by AnonW | July 4, 2019 | Reply


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