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Blog Entry# 3184830
Posted: Mar 08 2018 (22:46)

37 Responses
Last Response: Mar 18 2018 (20:20)
★★★  General Travel
Mar 08 2018 (22:46)   JBP/Jabalpur Junction

Obi Wan has taught you well~   3768 blog posts   1666 correct pred (74% accurate)
Entry# 3184830            Tags   Past Edits
1 compliments
Very Informative. Bookmarked.
This is a somewhat technical post, so apologies if someone gets bored to death while reading it :P :P
The figure that you see in Image 1 is called as a trapezoidal curve. this is a rather simplistic depiction of the velocity-time curve in traction, and will help me highlight a rather important point related to traction energy consumption
consider a train, going
from station A to B which are separated by 20 Km. Assume that the loco in question takes about 2 Km of distance to reach to full speed, and one Km to brake from MPS to zero speed at station. That means, for a distance of 17 Km (85% of the train's distance covered) the train is operating at MPS. assuming that frictional losses are negligible, you'll realize that for most of the journey, the train is in the part of the curve that is shown between T2 and T3 in the figure. since by Newton's first law we know that things in motion tend to stay in motion :P, if you ignore the frictional losses you realize that no energy is required by the train in time duration between T2 and T3. In reality we do have friction and train resistance loss, but they are quite small when compared to the energy required in time duration between T=0 and T1. Upto time T1 train has to first overcome inertia, accelerate from rest and then keep accelerating till it reaches MPS. this is where bulk of the energy required for locomotion is used, and beyond T1 and especially after T2, very less energy is required. in fact, in 3 phase locos, during the last phase i.e. braking, energy consumption is negative i.e. you return energy back to grid.
Now, not all trains have non stop runs of 20 Kms. passenger trains will have halts every 5-10 Kms or so, and suburban trains i.e. EMU's have halts every Km or so. As you might have realized, these trains require substantially higher power to move the same amount of load as they spend most of their time in 0 to T1 phase, and barely have time to coast as their schedule often don't permit them to go for lazy braking.
on other hand, fright trains, once in motion, can easily travel long distances without stopping. even when halted for OT/crossing, the time spent waiting is so much that they usually turn of their blowers after some time, thereby having very small losses when stationary. hence, even though quite heavy, freights actually require lesser amount of energy to move the same amount of load due to their motion characteristics
this whole "energy required to move a specific load per unit distance" is called SEC or Specific Energy Consumption, and is a very useful metric to see how energy consumption varies across pass and freight sector.
in the Image 2, you can clearly see how the SEC values for freight are almost one third of their corresponding values in passenger operation. in other words, you could say that over a given distance, a passenger train of 1500 tonnes (a full length ICF rake weighs this much) will take same amount of energy as a freight train of 4500 tonnes. many freight, like container or empty BOXN/BCN rakes weight much less than that, so you need less energy overall to operate them than you need to operate passenger trains, hence in newly electrified sections where some TSS are still under construction, preference is usually given to freight trains rather passenger ones in the beginning.
Image 1: click here
Image 2: click here
further reading (for those interested): click here (this is from BL Theraja's book A textbook on electrical technology)
tagged it under JBP, for its their RF's who are wondering about this for quite some time now :P if anyone has any objection to that, please tell me, I'll remove it.

15 posts - Thu Mar 08, 2018

17 posts - Fri Mar 09, 2018

Mar 09 2018 (17:52)
HOG WAM4 WAP1~   3698 blog posts
Re# 3184830-33            Tags   Past Edits
Many locomotives use the regenerative braking to supply Hotel load while passing through neutral sections.In neutral sections, as long as the train is moving faster than a predetermined speed limit, the on-board computer initiates a minimal dynamic braking effort. As the main circuit breaker is open in a neutral section, the DC link (for 3 phase locos) is powered by the traction inverters instead of the main transformer. This ensures an uninterrupted hotel load supply to the rake.
I wonder if the WAP7's HOG system or the upcoming composite converter in the WAP5 have such features.

Mar 09 2018 (19:41)
Obi Wan has taught you well~   3768 blog posts   1666 correct pred (74% accurate)
Re# 3184830-34            Tags   Past Edits
The cut out of Air Conditioner supply in neutral zones is one of the issues with HOG system, so it goes without saying that no AC power, either from motor or OHE is available to it at that time.
One Patna based RF once told me about how the LP of Patna Raj kept pressing BLHO switch at NZ, it probably is used to disconnect loco from supplying power to rake.
Doubt they,'ll change the system in P5

Mar 17 2018 (16:58)
HOG WAM4 WAP1~   3698 blog posts
Re# 3184830-35            Tags   Past Edits
Turns out, the HOG system in WDP4B locos is actually capable of taking up power generated during dynamic braking and supplying it as the Hotel load. Couldn't find anything similar mentioned in the specifications for the WAP7's HOG system though.

Mar 17 2018 (19:54)
Obi Wan has taught you well~   3768 blog posts   1666 correct pred (74% accurate)
Re# 3184830-36            Tags   Past Edits
I'm certain there isn't that feature in P7
Why was the diesel loco HOG project stopped?

Mar 18 2018 (20:20)
HOG WAM4 WAP1~   3698 blog posts
Re# 3184830-37            Tags   Past Edits
My guess is as good as yours.
It could be due to some loading restrictions. The HOG system in the WDP4B locos was apparently capable of handling 12-13 coaches only. This seems consistent with the fact that all three trains which ran on HOG with WDP4B locos initially (LKO-R Garibrath, LKO-BPL Garibrath and ANVT-KGM Shatabdi) were short rakes with barely 10 passenger coaches. The trials with 2 locos on the JP-JU intercity was probably done with 2 locos to avoid this issue.
one of the first HOG WDP4B's 40001 is already out of service and preserved now.

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