scope:

This document covers a.c. immune d.c. track circuits installed in single rail mode on a.c. electrified Network Rail Controlled Infrastructure.

The methodology considers both intact and faulty infrastructure. Limits are established for both continuous welded rail (CWR) and jointed rail (JR) track types.

The maximum permissible levels (i.e. the limits) of d.c. interference current in the tracks which will not cause a wrong side failure (WSF) (i.e. false operation of the relay), have been derived. The levels account for multiple trains, transmitter breakthrough and include an appropriate safety margin.

Standard train current and axle to axle voltage steady state limits are defined for the types of a.c. immune d.c. track relay currently in use.

Purpose

The purpose of this document is to provide a methodology to demonstrate compatibility with a.c. immune d.c. track circuits on the a.c. railway on Network Rail Controlled Infrastructure. This is achieved by:

• providing a set of standard d.c. interference current limits for steady state interference;

• providing a set of d.c. interference voltage limits for steady state axle to axle interference;

• providing a methodology to determine whether low frequency or transient interference will falsely operate a d.c. track relay.

These standard limits and methodologies will facilitate the demonstration of compatibility with d.c. track circuits for rolling stock, as part of a Route Acceptance Safety Case.