Lecture 6: Understanding 2x25kV ac traction system (Auto Transformer Feeding System) 

I was hunting for an explanation of the 2x25kV system (as I work in electricity transmission but not railways) and I have stumbled across this video. Great explanation! I'm very grateful - thumbs up from me.

Actually It's amazing that you were so kind to share all this knowledge. Thank you very much!

Excellent Very clear explanation

Hi there. This presentation was helpful in improving my understanding. Thank you for taking the time to share with us.

sir, your teaching skill is fabulous. so simple to digest and understand what you teach. thank u sir again.

your efforts are tremendous and Scott-T calculation you did so good!! Good Job Sir..

Great video. Thanks a lot!

Great explanation! Thanks

Excellent😊

Excellent sir

You made it so simple

Wonderful lecture-thumbs up from me son

Good information

Great video

Sir, why can't we centre tapped the secondary of Scott connected transformer as we are doing for V-connected transformer? Why we have to use Auto Transformer after Scott connected transformer?

It’s really a marvellous system. We recently energised an Autotransforner Substation on an existing 2 x 25kV railway , and despite an electrical engineering degree I was still a little confused during the energisation testing / section proving, how we managed to get both catenary and feeder busbars energised at 2 x 25kV by energising the substation via single feeder (in this particular instance it was via the -25kV track feeder). However, by sketching out an SLD, it becomes obvious that applying 25kV between any pole of the AT and earth, the flux developed in the AT core will then induce the opposite 25kV pole. Then when it comes to introducing all feeders from the track (and ultimately the adjacent feeder station) it become obvious why this method is so efficient.

Sir, can you pl explain the necessity for running AEC & BEC? Why can't we use only rail as return path?

What do the notations SSP and SP mean? And what type of connections are there and why they are required?

Is it necessary to install harmonic filters in traction substations 2x25kV?

Kindly post video about boundary post

thank you Sir

Very well presented, thank you! Would be interesting to see a comparison of RC vs BT vs 2x25kV in terms of losses in transformers, transformer kVA (capital cost) and short-circuit MVA.

8:16 I have seen other diagrams of 2 x 25kV systems but not explained in this understandable detail. Thank you. In your experience is it still necessary to add a separate feeder in parallel with the catenary and contact wire like in DC systems to increase current capacity of the circuit or is the contact wire in parallel with the +25kV feeder adequate for the higher current flowing in the subsections between ATs. Can you please share a single line diagram of whole system showing isolators, circuit breakers and track switches. What the the clearance between the +25kV and ~25kV feeders on mast poles and in substation. Is it the same as for 66kV as the next higher standard voltage

Hi there... The main advantage of 2x25 kV system over 1x25 kV system is to reduce the voltage drop by a factor of 2 for same load and at same distance. But this can be achieved by increasing the effective cross section of the catenary by running a feeder wire at the same potential as the catenary and then connecting it with the catenary at various locations. Why was this approach not taken in place of the 2x25 kV system explained in your video.

Hello, thank you for the video - very informative. I am looking to model an ATF system using LT spice, however I am having trouble setting up a reliable system: I have modelled the centre tapped transformer as two 25 kV (peak) 50 Hz AC Voltage sources with a 180 degree phase shift; the Inductors (used to represent the Auto transformers) as 0.2 H; The train as a resistive load of 80 Ohm. The issue is when I check the current in the Voltage sources, I am getting 800 A peak. This is far greater than the current in the resistive load, which reads 300 A. 1. I would like to know whether anyone is able to give any advice as to whether I can make any improvements with my model to yield more realistic results. 2. I am also aware that Lt Spice is typically used for lower voltage electronics modelling. Is anyone able to recommend a similar free (and new user friendly) application that may be more suited to high voltage circuit modelling? Many thanks.

When current ,I flows in +ve feeder & I flows in -ve feeder,I2R loss will be 2 times ,so same as 1ph * 25kV system,so how loss will be less,Can you please clarify ??

Nice sir

Where is complete ckt diagram which is show on the video first before started

Please tell me what is the difference between the Booster Transformer System and Auto Transformer System?

Hello. This was helpful but there is one thing I still don't understand: Looking at the 9:11 video time.... I don't see how the -25kV line negates EMI for lineside equipment between the two autotransformers where the train is.... since the autotransformers supply current for the train through the +25kV rail and it returns to them through the running-rails to the auto-transformer centre tap. Since we have higher current flowing through the running rails.... would this not expose lineside equipment to EMI?

Wonderful video. I have been working with 2*25 kV system but never got this type of clarity. Thanks for making this video. Do post this type of video. If possible plz share your number.

WoW!

Hi sir please do a video on metro train power supply distribution system i.e from panto to wheel

Do you knwo Static Frequency Converters (SFC) ?

👌👏

Sir, why don't we call here Booster Transformers, but as Auto Transformers

Hello Sir, Could you please share En standards you are referring to while explanation..that would help users a lot .

Hi, this video illustration the current flow is based on the voltage level of +25kV for catenary, 0V for rail, and -25kV for negative feeder. But since this is an AC system, so the voltage waveform of both catenary and negative feeder fluctuate between -25kV to 25kV am I correct? Because your video explain very nicely, but I am attempting to translate it into a single line simulation model. In simulation, the catenary and negative feeder is both connected to a 25kV busbar, am I correct?

Hi, I was rewatching your video again and wanted to ask what is the difference and benefits of using center-tap for secondary of supply transformer (So far I haven’t seen, with the systems where I work, center-tapped secondary). Thanks!

Hi will we have separate SSP and AT locations? If we do how physically we connect +25kv to catenary system? I mean should we connect through an overlap or directly connect to catenary by means of a 2 pole switch?

Great explanation! But can you elaborate more on the current distribution depending on the train position between two substations. As I understood, if train is in the middle then current distribution will be even (half and half). So, the question is, when train is closer to one of the substations, voltage drop decreases and current increases on the one side and opposite on the side of RR? And if yes, does it impact train load current distribution on the catenary (contact wire)? Example: Train load is 2I. Since the train іs closer to the substation on the left (as a reference to your circuit), let’s say that on the RR current splits 1.5I to the left and 0.5I to the right. On the auto transformers windings they gonna split evenly (1.5I/2 = 0.75I, 0.5I/2 = 0.25I). On the negative feeder side 0.75I+0.25I=1I, which will be added with 0.75I (auto transformer’s trolley winding), so train is drawing 1.75I from supply and 0.25I - return current from auto substation. Correct me if I wrong.

Hello Sahil, If I have railway system with 2x25kV,50Hz with autotransformer 50/25kV, how I calculate the impedance of the autotransformer with the general equation : Zat=(Uk%/100)(Un^2/Sn) ,so in this case,what is the value of Un, 50kV? or 25kV? Where: Uk% is the short circuit autotransformer impedance and Sn is the nominal apparent power in [VA] Best regards,Dennis