Indian Railways Thread

prahaar · Post by **prahaar** » 27 Jun 2015 20:10

Arshyamji, thanks for the update. I was out of date. What purpose do these wcams serve? They are used on this section only as a legacy?

Sachin · Post by **Sachin** » 27 Jun 2015 20:51

prahaar wrote: What purpose do these wcams serve? They are used on this section only as a legacy?

WCAMs was a neccessity when the route had both AC and DC power. Today as I understand that DC sections have been completely converted to AC. But if these locos are healthy and in good working order, they need not be thrown out. They will just operate in the AC mode. But IR may stop the manufacture of WCAMs loco soon; perhaps they may have stopped it already. So it is not using an equipment as a "legacy", they are getting operated because they can work equally well in the new mode as well. Why chuck out some thing which works well?

arshyam · Post by **arshyam** » 28 Jun 2015 02:46

That's right, and IR is notorious (in a positive sense) for maintaining and utilizing the equipment to the max. Most rolling stock have a codal life of 25 years, and 30 in case of locos. Compare that with our city buses that sigh and hang up their boots in 5 years!

The last AC/DC dual mode locos were built in the late nineties by BHEL. The WCAM-3 was the last model built in this series, and IIRC they capped it a 50/60 locos. I don't think they made more, though they might have made some goods versions, called WCAG-1. I am not sure of this bit.

@Prahaar-ji, before the conversion, the Mumbai area alone was under DC traction and used pure DC locos. But when the rest of IR started getting AC electric traction, these dual mode locos were needed, as it was not feasible to go up to a certain point with DC locos and simply switch to an AC loco, as the catenary can support only one mode of current at any given point of time and this switchover was time consuming: DC loco arrives, uncouples, moves to siding and powers down, current changed on OHE, then AC loco pulls up and couples itself to the rake and then starts. This easily took around 20 min. Hence the dual mode locos were used as a bridge, by using different pantographs depending on the traction. They hauled trains up a certain point on DC before switching pantos on the run and continued on AC till some station when they hand over to pure AC locos, which will haul the train for the rest of the way. This changeover usually happened at Vadodara on WR and Igatpuri on CR (toward Nasik).

Now that Mumbai has progressively switched over, IR has phased out all the old DC only locos, and relied on these dual mode locos to deal with the progressing AC/DC switch over point, the final point being CST (CR) or Churchgate (WR). Now that the entire system is AC, these locos are not needed, but since they have some life left in them (standard codal life = 30 years, WCAM-3s probably have another 10 years left), CR will use them in pure AC mode, but now send them further away as they are not needed exclusively in the Mumbai area as much as before. So you might see them hauling trains up to Nagpur too, as in their AC mode they can go anywhere on IR now, only limited by availability of pilots trained for this type.

But IR has been known to upgrade locos mid-way, in one of their POHs (periodic overhauls). Think of it as the MLU we know of in BRF. They will most likely upgrade the locos that have the most life left into pure AC and get rid of the DC equipment that's now occupying space uselessly. They might also make modifications for allowing higher speeds to match the red colour WAP-4 locos that form the backbone of IR today. They earlier upgraded the older WAP-1 locos to WAP-4 specs, so they might do something similar here.

Suraj · Post by **Suraj** » 28 Jun 2015 03:54

The WCAMs were more efficient in AC mode than DC mode. Some of them no longer even have DC equipment, since it has been removed and replaced with ballast, from what I read. They should in called WCAMinos (WCAM in name only). They sure do have a presence about them though - as nice looking as the WAP-4s, and my favorite looking IR locos behind the WAP5/WAP7s.

Singha · Post by **Singha** » 28 Jun 2015 07:19

the bankruptcy of our railway R&D has a new poster child in those simple bombardier EMUs for the mumbai locals seen above.

this is something we should have been doing in 1980s if we had been serious. these is nothing remotely HSRish about building some 100kmph EMU locals.

the two new factories coming up in bihar for next gen electric and diesel locos are our T90 and Armata deal.

Singha · Post by **Singha** » 29 Jun 2015 10:37

one of the bombardier rakes seems to have suffered a accident in churchgate yesterday, hitting the end damper on the platform, though no serious injury...attributed to human error by the motorman.

there is a CCTV video here. it was coming in way too fast.
http://www.firstpost.com/india/mumbai-f ... 16360.html

not sure if its bombardier or older rake..not that it matters.

Singha · Post by **Singha** » 29 Jun 2015 10:40

looks like it was older rake but same buffer had also pulled in a new rake earlier
http://www.mumbaimirror.com/mumbai/othe ... 857848.cms

prahaar · Post by **prahaar** » 29 Jun 2015 12:34

Thanks for the information Arshyam/Sachin/Suraj-ji. WCAMs have been my favorites due to the flexibility they include. Of course, now they are not needed, but good to see pragmatic usage by IR managers.

I tried to find details about the 9000HP Japanese locomotives which IR plans to procure for DFC, but details are quite sparse. I guess those locomotives are a waste if used without sufficient reducing congestion, in terms of hauling more freight, faster (hence limited to DFC). Is the suite-boot allegation, that is preventing Suresh Prabhu from going all out in prioritizing freight over passenger lines? Any way train-sets would not be for the masses (Viramgam Passenger/Virar Shuttle) but for the Shatabdi/Rajdhani crowd.

nelson · Post by **nelson** » 29 Jun 2015 15:25

Another day , another city; Chennai has its metro rail today...

arshyam · Post by **arshyam** » 29 Jun 2015 18:56

prahaar wrote:Any way train-sets would not be for the masses (Viramgam Passenger/Virar Shuttle) but for the Shatabdi/Rajdhani crowd.

Actually saar, the train sets are supposedly meant for precisely the Raj/Shatabdi type trains. And their shorter order run (only around 200 coaches) may not realize much by way of cost savings - IR can as well run these trains with the current coaches and dual locos if needed (they were doing some trials to realize this). Finally, without solving track congestion, running these trains (or trainsets) at higher speeds is going to be a dream.

prahaar · Post by **prahaar** » 29 Jun 2015 19:05

arshyam wrote:
prahaar wrote:Any way train-sets would not be for the masses (Viramgam Passenger/Virar Shuttle) but for the Shatabdi/Rajdhani crowd.
Actually saar, the train sets are supposedly meant for precisely the Raj/Shatabdi type trains. And their shorter order run (only around 200 coaches) may not realize much by way of cost savings - IR can as well run these trains with the current coaches and dual locos if needed (they were doing some trials to realize this). Finally, without solving track congestion, running these trains (or trainsets) at higher speeds is going to be a dream.

Sorry for not making myself clear, I was commenting on the same lines, as your views.

Train sets seems to be a "show of change" in the worst case and in the best case, it can allow IR to pilot feasibility of train sets with IR maintenance infrastructure/manpower. Sort of training the system to handle higher level technology, those with technical knowledge about such things, know better if this approach would have merit.

arshyam · Post by **arshyam** » 29 Jun 2015 19:10

Sorry, upon reading it again, I realized I mis-read your post. Agreed.

SaiK · Post by **SaiK** » 30 Jun 2015 04:34

metros should be designed to travel at around 160kmph.. why restrict them to 85kmph.. perhaps not enough distance to go that speed.

Theo_Fidel · Post by **Theo_Fidel** » 30 Jun 2015 04:59

Some mechanical engineer can clarify but doubling the speed typically quadruples the energy required. Esp. with severe losses during stop and start every 1-2 km. There are a few point to point metros that go faster. I believe the Reliance Delhi airport one is rated for 120 kmph. But then I remember reading of problems and it got de-rated. Not sure what it is now...

ArmenT · Post by **ArmenT** » 30 Jun 2015 05:47

Theo_Fidel wrote:Some mechanical engineer can clarify but doubling the speed typically quadruples the energy required.

Yep. Can be proved by the kinetic energy equation (i.e.)
KE = (1/2) * m * v^2
Where KE = kinetic energy, m = mass, v = velocity of object.

Therefore, for velocity v1, the kinetic energy is
E1 = (1/2) * m * v1 ^ 2

Now, if we double the velocity, then the kinetic energy for velocity = 2 * v1 is
E2 = (1/2) * m * (2v1) ^ 2
= (1/2) * m * 4 * v1 ^ 2
= 4 * E1

Therefore, for doubling the velocity, you need to quadruple the energy required.

Singha · Post by **Singha** » 30 Jun 2015 08:26

Theo_Fidel wrote:Some mechanical engineer can clarify but doubling the speed typically quadruples the energy required. Esp. with severe losses during stop and start every 1-2 km. There are a few point to point metros that go faster. I believe the Reliance Delhi airport one is rated for 120 kmph. But then I remember reading of problems and it got de-rated. Not sure what it is now...

I have been on that train. its a different one from the rest in that very little standing room and all fwd/back facing seats with luggage racks in each coach being a airport thing. it has just 4 stations IGI, Palam(board using a bus from domestic), shivaji stadium and rajiv chowk(CP). the quality of the coach is more tfta , and the stations are higher end also - like sliding doors on platform that seal off the tracks and a swank big stn like a airport under the CP regular metro station. a bit pricey but if more people can be encouraged its worth it....most users seemed to be airport employees

they had shut it down for a while after finding some defects in the rails/pillars at one point.
https://www.youtube.com/watch?v=eISJjPzIyUg

SaiK · Post by **SaiK** » 30 Jun 2015 18:00

^the dilli metro looks more TFTA.. and the chennai metro I guess intentionally made for cattle class!

https://www.youtube.com/watch?v=DqrdQ2lHywI
why does amma thinks cattle should only stand and not sit with comfort?

JMO.. but hard truth... this is more truth in many places where the locals themselves want to be cattle onlee

Karthik S · Post by **Karthik S** » 30 Jun 2015 18:31

^^ the seating arrangement is the same even in the Delhi metro. The above train is the airport metro express.

SaiK · Post by **SaiK** » 30 Jun 2015 19:08

feels good now

rajkumar · Post by **rajkumar** » 30 Jun 2015 20:47

SaiK wrote:^the dilli metro looks more TFTA.. and the chennai metro I guess intentionally made for cattle class!

https://www.youtube.com/watch?v=DqrdQ2lHywI
why does amma thinks cattle should only stand and not sit with comfort?

JMO.. but hard truth... this is more truth in many places where the locals themselves want to be cattle onlee

Its very simple you can cram in more people standing than sitting. Remember this is 'Mass Transit System (MTS)' hence we need to cram more people specially during the peak hour. The London Underground system has also adopted the same design philosophy and has more standing room than sitting. You should also consider the length of an average journey on a MTS, most journeys tend to be up to 45 / 60 mins.

Suraj · Post by **Suraj** » 30 Jun 2015 21:30

SaiK wrote:^the dilli metro looks more TFTA.. and the chennai metro I guess intentionally made for cattle class!

https://www.youtube.com/watch?v=DqrdQ2lHywI
why does amma thinks cattle should only stand and not sit with comfort?

JMO.. but hard truth... this is more truth in many places where the locals themselves want to be cattle onlee

Delhi Metro looks exactly the same inside, seating wise. So does Hong Kong, Tokyo, Osaka or Paris metros for that matter. None of them have seats like a bus. The only place where I recall seeing bus-like seating is on a couple of less busy Taipei metro lines. There's nothing wrong with Chennai Metro interior on first glance. It looks like any other contemporary one. It's going to accommodate high density transportation, and is designed accordingly.

Yayavar · Post by **Yayavar** » 30 Jun 2015 23:26

YEs, it is exactly same as Dilli metro. Though iirc Paris or other places certainly have coaches with more seats. Amsterdam is very luxurious. It is a function of population.

member_29068 · Post by **member_29068** » 30 Jun 2015 23:34

BTW Station, amneties and even the ticket vending machines look exactly like the Kuala Lumpur LRT system, and the coaches look like HongKong and Star LRT in Kuala Lumpur again.. actually coaches are identical to Kuala Lumpue Star LRT!

Suraj · Post by **Suraj** » 30 Jun 2015 23:43

yayavar wrote:YEs, it is exactly same as Dilli metro. Though iirc Paris or other places certainly have coaches with more seats. Amsterdam is very luxurious. It is a function of population.

Paris Metro has seating along the wall like Delhi or Chennai metros, at least on the lines I took and remember. Paris RER (the regional suburban train) has bus like seating, just like Mumbai suburban does. Likewise, Delhi Metro airport express has front facing seating, like Hong Kong airport metro does, while the regular MTR has side mounted wall seating like Delhi Metro. In fact, some of their rolling stock is the same Rotem EMUs used on Delhi Metro.

SaiK · Post by **SaiK** » 30 Jun 2015 23:53

http://timesofindia.indiatimes.com/indi ... 884198.cms

ticket-less travel is easiest thing to curb.
- airports have done it
- technology is available [cctv, without swiping, you are not allowed thru the one-way entry-check in
we have to go the airport way.. and security must be honest to not allow jump overs.
etc.

$120b in 5 years makes me feel good about desh.

- eram sci fi type toilets are mandatory for all coaches and stations.
- cctv and wifi mandatory
- better design of coaches for handling speed of 350kmph
-.. sky is the limit..that includes a restaurant and casino coach

.. perhaps a sport coach, where you can gym, exercise, play ping pong, carom, billards....

people would be willing to pay for services

Yayavar · Post by **Yayavar** » 01 Jul 2015 01:25

Suraj wrote:
yayavar wrote:YEs, it is exactly same as Dilli metro. Though iirc Paris or other places certainly have coaches with more seats. Amsterdam is very luxurious. It is a function of population.
Paris Metro has seating along the wall like Delhi or Chennai metros, at least on the lines I took and remember. Paris RER (the regional suburban train) has bus like seating, just like Mumbai suburban does. Likewise, Delhi Metro airport express has front facing seating, like Hong Kong airport metro does, while the regular MTR has side mounted wall seating like Delhi Metro. In fact, some of their rolling stock is the same Rotem EMUs used on Delhi Metro.

Probably different lines. I traveled to work many times -- been man years now -- and there were front facing seats. Basically much more seating than the standard Dilli metro. It may be that the newer ones are more like Dilli metro. I just dont have any memory of HK metro seating other than the train up the victoria peak.

Kashi · Post by **Kashi** » 01 Jul 2015 05:04

Suraj wrote:Delhi Metro looks exactly the same inside, seating wise. So does Hong Kong, Tokyo, Osaka or Paris metros for that matter. None of them have seats like a bus. The only place where I recall seeing bus-like seating is on a couple of less busy Taipei metro lines. There's nothing wrong with Chennai Metro interior on first glance. It looks like any other contemporary one. It's going to accommodate high density transportation, and is designed accordingly.

Actually the Tōkyū than run on Hankyu, Keihan and Kintetsu lines, despite being extremely busy have a bus like seating. One may argue that they are technically not metros since they connect different cities (and prefectures), but for all practical purposes they might as well be.

niran · Post by **niran** » 01 Jul 2015 07:15

front facing is for longer journey longer than 45 minutes from start to last station less than 45 minutes journey it is seats to the wall with large standing space in the middle the idea is for rapid under 2 minutes stops with front facing seats you cannot have under 2 minutes stops.

this is what i gathered about a decade ago in a meeting to decide whether to have front seating or wall seating.

nandakumar · Post by **nandakumar** » 01 Jul 2015 13:35

Theo_Fidel wrote:Some mechanical engineer can clarify but doubling the speed typically quadruples the energy required. Esp. with severe losses during stop and start every 1-2 km. There are a few point to point metros that go faster. I believe the Reliance Delhi airport one is rated for 120 kmph. But then I remember reading of problems and it got de-rated. Not sure what it is now...

I vaguely recall recall reading somewhere that the coaches ordered by Chennai metro are equipped with systems where the energy that would be otherwise wasted by a train decelerating on approaching a station, would be converted into electricity. google says there is something called regenerative brakes. I am not sure of the technical aspects. So if that were the case, then trains can be run at higher speeds isn't it? Also, higher speeds help in faster turnaround of train sets. A Koyambedu-Alandur run if completed in half the time could mean more traffic revenue per day. So even if these coaches are not equipped with special devices a case can still be made for higher speeds.

Sachin · Post by **Sachin** » 01 Jul 2015 15:20

nandakumar wrote:google says there is something called regenerative brakes. I am not sure of the technical aspects. So if that were the case, then trains can be run at higher speeds isn't it?

Regenerative brakes are not some thing unique to the metro trains only. Even the existing trains (and locos) have this facility. For a normal train with a diesel-electric loco, the diesel "engine" is like a generator, generating power enough to turn the even more power-ful traction motors. It is these traction motors which rotates the wheel. In an Electric loco, the generator facility is not required as the power to turn the traction motors comes from the over-heard wires.

When the regenerative brakes (I have also heard a term dynamic brake) are applied, the tractor motors starts working as dynamos - i.e generate power, instead of consuming power. The power generated in this fashion is fed into batteries for diesel-electric locos, or pushed back to the over-head wires in case of a electric loco. When a train is rushing into a platform, you can hear a very long "whine", and the train losing speed. This happens when the regenerative brakes are applied.

vsunder · Post by **vsunder** » 01 Jul 2015 20:08

Regenerative braking is due to Lenz's Law.

https://en.wikipedia.org/wiki/Lenz%27s_law

The production of the current will try to impede the process that manufactures it, i.e braking. A very vivid and simple experiment to illustrate this can be done as follows. Take a long straight copper tube.
Hold it vertical. Drop a metal bar through it and it will fall quickly. Now drop a tiny bar magnet and it will take it's own sweet time to fall out at the bottom. Basically the moving bar magnet sets up a current in the copper tube. The direction of the current is such that it impedes the downward motion of the bar magnet due to gravity. The difference in time between when the magnet falls out and when the unmagnetized bar falls out is significant and striking. Lenz's Law is incorporated into the famous Maxwell equations in electromagnetism as the negative sign on the right side in the third equation in the list below:

http://www.maxwells-equations.com/

As far as I know there is no analog of Lenz's law for fluids, the equations for incompressible flow( low speed aerodynamics) parallels the equations of electromagnetism, in particular magnetostatics( thus no Lenz's law).
Transonic and supersonic flow is compressible flow and a different animal.
https://en.wikipedia.org/wiki/Maxwell%27s_equations

Suraj · Post by **Suraj** » 01 Jul 2015 20:39

Kashi wrote:Actually the Tōkyū than run on Hankyu, Keihan and Kintetsu lines, despite being extremely busy have a bus like seating. One may argue that they are technically not metros since they connect different cities (and prefectures), but for all practical purposes they might as well be.

And on the other hand, the Yamanote line, which isn't quite a subway either but under JR rather than the Tokyo Metro/Toei systems, has wall mounted sideways seating. The ones you quote are (I think) trains that run into the city from the outer suburbs/exurbs . These tend to much longer to get into the city, and don't get anywhere near as famously crowded as Yamanote. It could be argued that the difference is the pattern of crowdedness. A train traveling radially will build up passengers, which means the ones entering farther out get to sit because they're traveling much longer. Yamanote on the other hand, is a circular line, and therefore is crowded for significant parts of it during morning rush hour (I have never tried to wade through it then!). Therefore it makes sense that a radial line with less traffic has bus seating, and a circular line with much more traffic has wall seating.

SaiK · Post by **SaiK** » 01 Jul 2015 20:54

tell me if you didn't enjoy the scenery.

nandakumar · Post by **nandakumar** » 01 Jul 2015 21:06

Sachin, vsunder
My question still remains. If coaches are equipped to conserve energy lost due to braking, shouldn't trains be made to run at higher speeds? Also the larger question of economics. If energy costs are a relatively smaller portion of the total operating costs (I should think that to be the case with 15,000 crore in capital cost with two thirds of that in yen currency loans for Chennai Metro) it pays to flog the assets a little more?

nandakumar · Post by **nandakumar** » 01 Jul 2015 21:13

SaiK wrote:tell me if you didn't enjoy the scenery.

My best train journey was between Bangalore and Pune in the early 70s. The stretch from Harihar and all the way to Pune via Sawantwadi, Nira etc was too picturesque to describe. I havent travelled on konkan railway. But I am told that it is way more beautiful than Bangalore Pune line. The video only proves it.

vsunder · Post by **vsunder** » 01 Jul 2015 21:58

nandakumar wrote:Sachin, vsunder
My question still remains. If coaches are equipped to conserve energy lost due to braking, shouldn't trains be made to run at higher speeds? Also the larger question of economics. If energy costs are a relatively smaller portion of the total operating costs (I should think that to be the case with 15,000 crore in capital cost with two thirds of that in yen currency loans for Chennai Metro) it pays to flog the assets a little more?

I think you seem to want to prolong a discussion when none is there. The key word is conserve. Wherever did you get the idea that all the braking effort goes into producing electricity, a very, very large amount simply goes into producing heat which is completely wasteful and there is no efficient way to recover that. You might want to dust off a BSc first year book on Physics and read the chapter on non-conservative forces in the section on Basic Mechanics. There have been umpteen posts here about increasing speeds. It seems these posters either cannot read or cannot count. There has been a substantial discussion here on the state of tracks in India and how at the current time it is next to impossible to increase speeds given the state of the tracks, the signalling equipment and heavy traffic sharing routes that are long overloaded, with more trains and freight. If you do not address that and that is a major effort you will not have higher speeds. If some of you want gyms, playing ludo, snakes and ladders and seven tiles, while traveling in IR, you can do so on Golden Chariot paying a premium, it has what you want, but filling the thread with nonsense is simply counterproductive.

vsunder · Post by **vsunder** » 01 Jul 2015 23:46

Power derived from regenerative systems is not easy to implement. This is particularly true in AC systems which is by now the only system on IR. The reason is that when the current is fed back into the grid, it must match the phase and the frequency of the wire overhead. Notice the phase is not constant as the loco moves. There is a sequence of posts above involving me and Arshyam on neutral zones and phase matching and why there are neutral zones. So there has to be equipment in the loco that can sense the correct phase etc. ( more precisely the waveform)as it changes every 40km or thereabouts, whenever the loco moves to a section with a different sub-station. Or else the system will trip. Also there must be equipment at the sub-stations to detect surges and potentially feeding power into the system will create a surge, so somehow the system must know that, to differentiate between a good surge and a bad surge for want of a better name, in principal lightning can strike a system and that is a no no for the system. It would seem and I am ignorant on these issues that power derived from regenerative braking would work best on sections that have a large number of locos operating, busy sections. Then power sent into the system would not send too many surges and potential tripping at the substation. The substation will surely have a means to protect itself from such damaging surges. A truly bad scenario would be 20 locos operating on the section and all braking at one given instant, statistically will not happen but an interesting possibility. A good scenario is 20 locos operating on the section, voltage at 20Kv, 5 kV from the normal 25 Kv and one loco braking and giving power, no surge in voltage. Some of these issues may be handled by using microprocessors but one must desist from the notion that it is simply some easy gimmick like attaching wires from the brakes to the overhead wires and there voila we have le systeme.

Theo_Fidel · Post by **Theo_Fidel** » 01 Jul 2015 23:48

nandakumar wrote:Sachin, vsunder
My question still remains. If coaches are equipped to conserve energy lost due to braking, shouldn't trains be made to run at higher speeds? Also the larger question of economics. If energy costs are a relatively smaller portion of the total operating costs (I should think that to be the case with 15,000 crore in capital cost with two thirds of that in yen currency loans for Chennai Metro) it pays to flog the assets a little more?

Nandakumar saar, not vsundar but,

Its not that simple. Regenerative braking may give you back 1/3 the energy back at best of circumstances. As vsundar saar says the regenerative piece is a challenge in itself and the system has to be designed to handle it all the way back to the power plant. Also the physical infrastructure has to be upgraded to handle speeds. Notably the maximum curvatures revised, esp. in tight city streets. If you want 160 kmph the systems has to be designed for that from the start and one needs to pay for it. It can all be done, at the right price.

Also consider passenger comfort. Right now the acceleration max for metros is limited to ~ 1 m/sec2. So to get to 160 kmph ~ 44m/sec you would need to accelerate for roughly 44 seconds. Consider acceleration from zero d=v0*t+1/2*a*t2; d=0*44+1/2*1*44^2= 968 meters. So it would require ~ 1 km just to get up to speed and then another km to decelerate to zero.

In the context of metros in dense cities with stops every 1-2 km, simply not worth its saar.
------------------------------------------

WRT the coaches, I still think India will come to regret putting SG coaches on our lines. There is no real reason we could not have provided BG coaches on SG lines & Boggies other than E.S hard headedness. Our Metros look cramped compared to the suburban's because of that. But its too late for this now. Maybe for future lines in high density areas BG loading gauges should be considered.

member_29001 · Post by **member_29001** » 02 Jul 2015 02:16

Regarding SG vs BG for Metros; first line of Delhi Metro was built as BG because IR wanted interoperability. But, E.S. being an ex-IR insider chose SG for subsequent lines to avoid being Kargilled by IR. Anyway, state govts are only too happy to keep Metros outside IR control.

vsunder · Post by **vsunder** » 02 Jul 2015 04:05

As I remarked above, regenerative systems are easier to implement on DC systems as one does not have to deal with issues of frequency, phase etc. There is still the issue of the system sensing the surge, but this is not a major issue. My understanding is that amongst all the metro systems installed in India now, only Bangalore Namma Metro runs on 750V DC, while others like the Chennai system, Mumbai and the Hyderabad system are like IR, 25Kv, overhead catenary. Thus a regenerative generation system will be quite easy to put into the Namma Metro system, for the others there are some technical issues to overcome for the reasons indicated above.

https://en.wikipedia.org/wiki/Namma_Metro

The Kochi Metro system when functional will also be 750V DC.
IR system is pegged at 25Kv, but variations from 20kv to 30Kv are common and locos are equipped to deal with such surges. Just like the surge suppressors in a home power supply.