2002 Track circuit cal.

[Peter]

I am a bit confused for the calculation of it. Could anyone point out my mistakes?

Can i use the pickup current only as shown in the attachment to calculate the feed resistance? So, it will only include Ballast Resistance, Relay Resistance and Feed Resistance.

From another post, it shows an approach by assuming the drop away % is 65% of Pick-up current. It will include Shunt Resistance, Ballast Resistance, Relay Resistance and Feed Resistance in the calculation. The Feed resistance will be about 3.36ohm.

Which one is correct??

Thanks in advance!!

What you have worked out there is the maximum value for the feed resistance at which the relay will pick up. Given all of the other characteristics of the track circuit (including the drop away which, unless it is stated in the question, is generally assumed to be around 65% of the pickup), you would then be able to work out the value of shunt required to drop the track circuit.

Unfortunately, for some reason the 2002 paper is one that I do not have in my collection to see what they actually asked, but you are likely to be asked to set up the track for "reliable operation". I have not done the sums, but that value of Rfeed seem high and I suspect that you would find a high drop shunt value meaning that the track will be prone to drop for small changes in ballast resistance (eg rain making the ballast wet) and hence making it possibly unreliable.

The simple answer to your question is that you may have to consider both the calculations that you speak about in order to prove that the TC will work.

Peter