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Regenerative braking
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samuelmorris
Established Member
I'm not sure why it should have come about then (presumably improvements in solving the issue of putting the current back into the supply), but the Hitachi 465s still use regen braking now don't they?
Manchester77
Established Member
Wasn't it part of the upgrade of the network from 660 volts to 750?
Yes they do. I was talking about Alsthom 465s.
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As far as I know the voltage has always been 750V DC.
JB25
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They reckon so I heard the reason for the Sutton explosion and the Victoria power out the other week may have been down to Regen braking.
That's interesting. Which power out was that? Was it the one that was during the morning peak, around 8?
swt_passenger
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It hasn't always been 750V DC. That's just a 'nominal value', basically to avoid having a whole range of different numbers on warning signs etc. Most parts of the South London inner suburban area still operated at 660V until very recently, the ongoing NR 'DC regeneration' project raises the normal voltage to 750V, but it will not be completed in SWT's area until the S stock introduction is complete in 2016, because the NR and LU power supplies are not separated, and C and D stock cannot deal with 750V.
JB25
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The one the day after Sutton. Apparently the 377/6s may somehow be putting too much juice back in from Regenerative Braking which was blowing the circuits so to speak.
edwin_m
Veteran Member
The actual voltage in the third rail or overhead line fluctuates quite a lot around the nominal value. This is necessary for regenerative braking to work, because when a train is regenerating the current flowing through the resistance of the rails/wires increases the line voltage near the train. If the voltage goes about the maximum the train needs to detect this and stop regenerating because there is no other train near enough that needs the power.
There was also a safety issue about a train regenerating and running into a section that has been isolated for people to work on it, possibly causing that section to go live. This problem has now been resolved but I'm not sure how.
There was also a safety issue about a train regenerating and running into a section that has been isolated for people to work on it, possibly causing that section to go live. This problem has now been resolved but I'm not sure how.
This explains why trains also have rheostatic braking in addition to regenerative.
Coming back to your original post...
Yes the 375, 376 and 377 units began having regenerative braking installed during mid 2008, even though talks began as early as 2006 I believe, so I can confirm what you've heard there. The Networkers were all delivered with regen braking, but I don't know what happened that meant they stopped using the regen braking in 2008 on Altshom's units if that's the case.
P.s it might be helpful to clarify in your first post that you're talking about GEC Alsthom's 465/2, 465/9 and 466 units.
I don't know about the networkers, because I thought they didn't regenerate before 2008 either except for the AC variants.
Anyway, this is the simple version... the problem about DC regeneration is that the current generated cannot go back into the grid, as there is no facility to switch the DC to AC in the substations. So the current has to be used by other trains in the same electrical section.
The difficulty arises if there is a fault in the section at the same time as a train is generating. There are detecting devices which automatically cut out the power in the section of there is a short circuit (e.g. a cable fault, or something in contact between 3rd rail and earth, e.g. A short circuiting bar) to protect the infrastructure from damage. A train regenerating at the same time as a fault occurs effectively masks the short circuit, meaning that it would continue to short circuit, potentially causing serious damage to the infrastructure.
What happened in 2008 is that some alterations were done to substations, but mostly it was the culmination of many years work by some very clever electrification and traction engineers which demonstrated that the trains were smart enough to detect the difference in voltage and current in the con rail when it is being short circuited, and thus would not regenerate in those circumstances.
Anyway, this is the simple version... the problem about DC regeneration is that the current generated cannot go back into the grid, as there is no facility to switch the DC to AC in the substations. So the current has to be used by other trains in the same electrical section.
The difficulty arises if there is a fault in the section at the same time as a train is generating. There are detecting devices which automatically cut out the power in the section of there is a short circuit (e.g. a cable fault, or something in contact between 3rd rail and earth, e.g. A short circuiting bar) to protect the infrastructure from damage. A train regenerating at the same time as a fault occurs effectively masks the short circuit, meaning that it would continue to short circuit, potentially causing serious damage to the infrastructure.
What happened in 2008 is that some alterations were done to substations, but mostly it was the culmination of many years work by some very clever electrification and traction engineers which demonstrated that the trains were smart enough to detect the difference in voltage and current in the con rail when it is being short circuited, and thus would not regenerate in those circumstances.
millemille
Member
Southeastern operated Electrostar's have been capable of regen braking since the outset but started regen braking in 2008/2009 after the infrastructure was finally able to cope with regen.
The 465/0/1's/ were able to regen brake in 2009 after the Hitachi traction kit got it's safety case for regen operation.
465/2/9 & 466's have never regen braked.
The 465/0/1's/ were able to regen brake in 2009 after the Hitachi traction kit got it's safety case for regen operation.
465/2/9 & 466's have never regen braked.
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JB25
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We aren't allowed to touch the shoe gear or shoe fuses on 377s like we can on a 455 for the same reason. Even though the shoes could be paddled up from the conductor rail, there is still the fear that there is some residual current. Obviously no one is willing to be a guinea pig to test the theory out.
We aren't allowed to touch the shoe gear or shoe fuses on 377s like we can on a 455 for the same reason. Even though the shoes could be paddled up from the conductor rail, there is still the fear that there is some residual current. Obviously no one is willing to be a guinea pig to test the theory out.
A guinea pig? All you need for that is a multimeter! Most can measure pretty high voltages.
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