Rheostatic Braking

[Elecman]

From memory, at least some of the feeder stations on the Woodhead electrification had resistor banks which were switched in to absorb the regen braking energy if necessary i.e. when there were no other trains around to use it. I think there were maintenance issues with that equipment later on, so it may have been taken out of use. That may also have been a factor in adding rheostatic braking capability to the locos.

That’s correct one of my lecturers at college was involved in the electrification and he said the substations had resistance banks for exactly that reason to absorb excess power from the system when no other train was absorbing it.

 

[darwins]

I thought that on the contrary 'O stock' not only had braking resistors but due to the fact the substations and power system were not really designed to accept regeneration that more often than not the 'O stock' reverted to rheostatic braking instead of using the regen.

Had a chance to check a copy of Agnew today. We are both partly correct, they did have some capacity to put the power through resistors, but this was limited, after which the dynamic braking was disconnected.

He states "When an over-voltage is generated by the Metadyne due to the line not being able to absorb the regenerated power, contactor EG again closes, thus connecting a portion of the entry resistance across the primary brushes. Should the voltage continue to rise after the resistance has been switched in, over voltage relay No 1 operates and disconnects the Metadyne from the line."

 

[hexagon789]

Had a chance to check a copy of Agnew today. We are both partly correct, they did have some capacity to put the power through resistors, but this was limited, after which the dynamic braking was disconnected.

He states "When an over-voltage is generated by the Metadyne due to the line not being able to absorb the regenerated power, contactor EG again closes, thus connecting a portion of the entry resistance across the primary brushes. Should the voltage continue to rise after the resistance has been switched in, over voltage relay No 1 operates and disconnects the Metadyne from the line."

View attachment 107246

Many thanks for digging it out, quite interesting to see the circuit diagram.

Trying to fathom out the abbreviations for the sequence of contactors - "S" is presumably "Series" and "R" is "Resistance" but the others I can't quite place.

 

[supervc-10]

AFAIK only in the sense of being able to power the auxiliary loads (fans etc.) from the traction motor power - they don't have any energy storage.

This sounds broadly similar to the way that a modern non-hybrid car will charge the battery and run the accessories when braking.

Will the Class 93 work closer to a plug-in hybrid car? Where they will work off the overhead when they can, but top off the battery using regen too?

 

[ac6000cw]

Not the case. 745s only have regen braking, falling back to friction braking through neutral sections. There may be other traction with a similar setup.

I believe that the 755 bi-modes have rheostatic braking in diesel mode at least, based on what was said in a Modern Railways article in 2018: "As with other electric trains, regenerative braking allows energy to be fed back into the overhead line equipment when trains are slowing down and a ‘brake resistor’ comes into play when the BMUs are on diesel power, meaning brake pads last longer and less dust from the brake shoes is released into the environment." and personal observation of the heat haze over what look like roof mounted brake resistor grids after coming to a station stop.

Will the Class 93 work closer to a plug-in hybrid car? Where they will work off the overhead when they can, but top off the battery using regen too?

From memory, I think that is the idea, but of course how much benefit you can get from it depends on how fast the battery can be charged.

The US manufacturers ("Dynamic braking" over there) offer a range of capacities, up through Extended Range Dynamic Braking, which I guess is being referred to here, with huge brake resistor elements along the roofline. Only those railroads with substantial downhills and main line freights order these, often with four or so such locomotives all braking like this.

'Extended Range Dynamic Braking' means it works down to lower speeds than earlier versions - down to around 6 mph or less. I think the term 'High Capacity' means having the same (or higher) braking capacity as for traction.

While years ago the 'flatland' railroads generally avoided paying extra to have dynamic braking on locos, the coalescing of most of the railroads into four US and two Canadian mega-railroads has meant that they normally buy 'do anything, go anywhere' mainline locos with dynamic braking as standard. In fact we seem to have reached the stage in the US where the only major buying choice is whether the loco has all six axles powered or only four out of six, and in some mountainous areas trains are not allowed to operate without sufficient working dynamic braking capability (for safety reasons).

 

[Shwam3]

I believe that the 755 bi-modes have rheostatic braking in diesel mode at least, based on what was said in a Modern Railways article in 2018: "As with other electric trains, regenerative braking allows energy to be fed back into the overhead line equipment when trains are slowing down and a ‘brake resistor’ comes into play when the BMUs are on diesel power, meaning brake pads last longer and less dust from the brake shoes is released into the environment." and personal observation of the heat haze over what look like roof mounted brake resistor grids after coming to a station stop.

Correct, 755s have rheostatic braking in diesel and electric modes which, somewhat counter-intuitively, makes them perform better through neutral sections than the pure electric 745s.

 

[notadriver]

Sometimes the braking technique can be adjusted for those units whose regenerative/rheostatic braking is disabled through neutral sections. Not doing so can leave a ‘burning’ smell from the brakes when arriving at a station.

 

[paulkidger]

507s & 508s have them, and disc breaking, I believe.

My professional interest was Energy Management therefore this taints any interest I have in railways.. I was at a conference where someone from LUT reported on a problem experienced due to regeneration. Apparently the ventilation fans ran off the DC supply and local residents were complaining of excessive noise early in the morning. It turned out that there was an imbalance between the regen and the power drawn during certain early morning operating patterns, This resulted in a higher DC voltage and increased fan speed hence noise.
DC lends itself to regen, I believe this was the case with the Woodheads. With regen, operation was almost like a funicular with descenting trains regenerating and helping to power the ascending trains. With AC, I guess that it is only recently that the electronics have become available to be able to push 50 Hz back into the OH. I think the potential is for a 20% energy save by recovering the kinetic energy, obviously this depends on the operating pattern with Metros offering the best saving.
LUT provided a crude but effective form of regen on some of the tube lines by having the tracks rise on a station approach and fall on departure, purely mechanical, no electronics, no problems with upsets to the line voltage.

 

[Ken H]

My professional interest was Energy Management therefore this taints any interest I have in railways.. I was at a conference where someone from LUT reported on a problem experienced due to regeneration. Apparently the ventilation fans ran off the DC supply and local residents were complaining of excessive noise early in the morning. It turned out that there was an imbalance between the regen and the power drawn during certain early morning operating patterns, This resulted in a higher DC voltage and increased fan speed hence noise.
DC lends itself to regen, I believe this was the case with the Woodheads. With regen, operation was almost like a funicular with descenting trains regenerating and helping to power the ascending trains. With AC, I guess that it is only recently that the electronics have become available to be able to push 50 Hz back into the OH. I think the potential is for a 20% energy save by recovering the kinetic energy, obviously this depends on the operating pattern with Metros offering the best saving.
LUT provided a crude but effective form of regen on some of the tube lines by having the tracks rise on a station approach and fall on departure, purely mechanical, no electronics, no problems with upsets to the line voltage.

Saw tooth and hump profiles as Paul mentions were used long before LT. The Central London Railway used them before WW1. They are still there, of course!