Regen braking R1 class 2029

 
  edison Chief Commissioner

Well-enough known that 2029 had regen (dynamic?) braking for the Neutral Bay wharf branch.
What controls were operated by the driver to bring this facility into operation?

Edison

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  Sydney_Gunzel Chief Commissioner

Location: The Red Lines.
Well-enough known that 2029 had regen (dynamic?) braking for the Neutral Bay wharf branch.
What controls were operated by the driver to bring this facility into operation?

Edison
edison
An article by Noel Reed and Ian Saxon in the February 2010 Trolley Wire, "Dynamic Braking tests for Sydney's Neutral Bay line" describes the testing of and in-service operation of "dynamic drag" equipped R1 2029.

Back issues are available at the Tramway Museum, Loftus.
  edison Chief Commissioner

Sydney_Gunzel  -  Many thanks.

Edison
  matthewg Train Controller

I can't find my February 2010 Trolley Wire, so I can't look up what controller they used, but 'dynamic brake' trams were and are common, just not in Australia.
The normal way to activate them was simply to rotate the controller past 'off', and the further you turned the controller the stronger the electric braking effort.

For some reason electric braking was not favoured in Australia. The Brisbane 'droppies' had electric brakes when they were handbrake cars, but as they were converted to air-brake, the electric braking was blocked out.

The British had really odd ideas - many of their cars from various cities were fitted with graduated electric braking, but was considered to only be an emergency brake. I've been on a Blackpool 'hand brake' car that was fitted with a 7 to 8 notch electric brake, but it was only to be used for emergency stops, all service braking was with a goose-neck handbrake lever. And it wasn't because the electric brake didn't work, we tested the electric brake in both directions as part of the car prep. It worked and worked very well, but the convention is not to use it as a service brake.


I can say that these old style electric brakes do take some getting use to, as the response time is inverse to speed, so if you are going slowly they take several seconds to have any effect, but the faster you are going the faster the braking effect cuts in.

On the steep Neutral Bay a dynamic brake would have made the car a lot easier to drive down hill and would have save considerably on brake wear.
  edison Chief Commissioner

Matthewg - Thanks for the comments and info. Will continue the search for the issue of TW.

Edison
  matthewg Train Controller

But series machines don't work well as generators even though in broad principle they can. The problem with a series generator is that a series field current is needed to produce the magnetism needed to produce armature voltage which is needed to produce a current for the series field. A bit like a dog chasing its tail...
3l diesel


Connect a pair of series motors 'back to back' and they will dynamic brake - the residual magnetism in the motor assemblies causes enough current to be generated to create weak field in the other motor (which is doing the same thing) and once the fields start to increase, the motors start 'fighting' each other.
Most Australian 4 motor trams can be 'fourth emergency' braked, throwing the reverser key back. Cause the motors to be cross connected in such a way they excite the field in their opposite pair and cause a contra rotation effort. The two motors so connected do it to each other simultaneously.

The electric braking controller just does this in a controlled matter with external resistances added to moderate the effect.

You could also separately excite the field winding from the overhead and have the armature produce voltage and current immediately as well...



I believe some trains use separate external excitation of the fields. The down side of this method is that if you lose overhead power, you lose the brakes. I believe some trains/trams use batteries to get around this issue.

The 3 different dynamic brake trams I've operated all were of the 'self exciting' type, so that if the pan/pole was to become damaged/off, the dynamic brake still works. On two of the types (both German, and apparently 'east' and 'west' versions of the same basic controller), the primary brake is electric. The hand brake provided is really only for holding after the electric brake has slowed the tram car down to a crawl. With out the dynamic brake, the hand brake simply wouldn't stop the car, so the dynamic brake is appropriately engineered for reliability. Both German trams had electro-magnetic track brakes energised by battery for the ultimate emergency stop as well, but you don't want to use the track brake unless the situation really is dire. They are nasty.


Most of the 'complexity' of a dynamic brake tram car is in the controller - extra positions for the control drum and extra contacts and wiring, and given the amount of hardware in an air-brake car, on the overall complexity front, they probably come out even.

But as an operator you don't' see all that, you have have a handle you can rotate past 'off' into 'brake'. (And a brakes that have 'interesting' delayed activation characteristics).
  Fred Scuttle Junior Train Controller

Location: Point Clare, NSW
There was a description of the operation of R1 2029's dynamic braking system in the July 1973 issue of Electric Traction (now Transit Australia). It was one of a series of articles on the R and R1 classes by Ross K Willson, entitled "The Sydney Corridor Tramcars". (late '72 - mid '73). The more recent Trolley Wire article looked at R1 2029 in more depth. The Electric Traction article makes the point that the braking system used was definitely dynamic (traction motors operating as generators dissipating power as heat through resistor grids) as opposed to regenerative (where power is fed back into the overhead). A regenerative system would have been impracticable on the Neutral Bay line, as there would have been, at most, only two cars operating the shuttle service (2029 and a K class car), which would have been insufficient to absorb any regenerated power. Mentioned in both articles is the role played by R1 1999, which operated on the Neutral Bay line as a test car temporarily fitted with dynamic resistors (and measuring equipment) in early 1952. The ARHS would have a copy of the relevant issue of Electric Traction in its research library.
  matthewg Train Controller

Matt, just trying to visualise the configuration of the motors, do I understand that the field winding of one motor is connected in series with the armature of a companion, and likewise for the second? I can't quite get my head around how it might work, so if you have time, further comment would be appreciated.
cheers Vaughan.
3l diesel

I don't have diagrams of a dynamic brake car, but I do have diagrams of Sydney and Melbourne car electrics.
I also can't quite get my head around the psychics involved. (right hand rule, magnetic flux, induced currents, etc), which makes it difficult to explain.

All motors can be generators.
In the 4 motor cars - the motors are always in parallel pairs.

The field coils are always in series with each armature of it's own motor (It is after all a 'series' motor, if the fields were not in series it the motor would have another name!).
Series motors are used as they are simple to control and have great starting torque.


All motors when running are also generators. A series motor reaches it's maximum speed for a given load when the 'Back ElectroMotive Force' it is generating is fully counteracting the input voltage. (Balancing speed).

If the reverser is off, the armature and fields are disconnected from one another. The car will freely roll. The magnetism is still there, but electricity needs to flow.

If the reverser is forward, the motors are connected to one another, but the car will roll forward as the 'back EMF' generated by the motor will counteract and neutralise the fields, the whole generator/motor effect is rendered ineffective.

If the car rolls backwards however, the generated force is no longer 'backwards', but instead re-reinforces the weak residual fields and the motor generates more and more power. This power feeds into the paired motor, which then tries to rotate in the opposite direction. At the same time this other motor is also generating power and trying to drive the first one backwards.

A single motor on it's own can brake - this is called 'plug braking' and is often used on things like electric forklifts and golf carts. They disconnect the supply (the battery) throw the motor into reverse (reverse either the field or armature polarity) and short the output. The generated current is forced straight back into the motor. The motor effectively tries to drive itself in reverse. The motors get pretty hot pretty quickly. Forklift motors are built to take this sort of punishment.

The '4th' emergency as taught to tram drivers is a form of dynamic brake - 'pull the key back'. By putting the tram in reverse, even with out applying any power the motors get into a configuration where the fields reinforce instead of collapse, and the resulting braking effect is savage. If done at any speed, the voltages generated can ruin the motors.

Dynamic braking is just 4th emergency with external resistors switched in to control the amount of force generated. The physics is the same.

But they don't explicitly cross connect the fields and armatures as you suggested. The armature and it's field stay in series with each other. It's just connected to another motor in similar configuration. The key to making it work is the motor has to be 'reversed'.
You reverse a series motor by swapping the polarity of either the armature or the field. Swap both and the motor keeps going in the same direction.

So on all the trams, the field and armature connections all run up to the reverser drum, so while the armature and it's field always stay in series, a mass of wires go to the reverser drum so they can control which polarity is applied the armature and the field together.

I've probably just confused things more Smile. I really need a refresher on my high school physics.
  Fred Scuttle Junior Train Controller

Location: Point Clare, NSW
The 1972 Electric Traction article described (as I recall) some of the ins and outs of the dynamic system as devised for R1 2029 in in some detail. I've got a copy of the relevant issue of the magazine buried here at home somewhere - once I dig it out, I'll post the pertinent bits.

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