2010 Track Circuit Question

[Peter]

Hi all,

Even I ended up with a TC Length of 3Km.

My concern is about the Drop shunt when the Ballast Resistance is around 1.5 ohmkm. The drop shunt current ended up with a negative value. :-(

Regards

Given the values in the question, that is a distinct possibility. That is what happened when I went through the numbers. If you did the calculations with the numbers given not adding in any contingency (as I did at first to work out the worst case to comment on what you would do in reality), you get a TC length that will not pick with the changed value of ballast resistance. I think that if you add 10% margin, you get about 3.4km for the first part and then a track that has a DS of about 9ohms.

Having a TC that does not work when the ballast resistance gets worse is fine if the question is "comment on the effect of the ballast resistance changing to 1.5 ohm km" but as the question was "calculate the DS" I would expect there to be a possible answer.

Provided that you commented on the meaning of a negative number as the answer, I am sure there would be some credit, and if the arithmetic was good, you must get marks for that.

Have a look at the model in this post with the numbers from the exam and you'll find that your 3 and a bit kilometre track is what the numbers deliver.

Above all, don't panic, you cannot change things now!

Peter