scope:

The scope of this procedure is that of providing a method for presenting calculations in support of a safety case for the operation of electric trains over TI 21 track circuits. All components relevant to TI 21 track circuits are considered.

The document only considers double rail configuration with balanced earth connections.

The electrification installed is assumed to be of the standard arrangement, autotransformer fed sections of railway are not included.

Traction bonding is assumed to be compliant with the requirements of RT/E/PS/11761 [2].

Purpose

The purpose of this procedure is to provide a method for calculating the safe permissible maximum levels of electrical interference that may be generated by electric trains designed to be used on tracks employing TI 21 track circuits. The procedure lists all of the infrastructure aspects to be taken into account, characteristics of the TI 21 track circuits and possible failure modes. Worked examples are given for calculating maximum permissible levels of electrical interference due to traction current, and axle-to-axle voltages.