Page 406 - IRSEM_Main Book

Para No. 17.5.2(i) Annexure: 17-A1

Measurement of Stray Direct Current before Installation of
DC Single Rail Track Circuits

1.0 Before installing a DC Track Circuit in areas, which are to be AC Electrified, stray Direct
Current tests shall be carried out so as to ensure that DC Track Relays shall not operate
with the stray currents.

2.0 These Tests shall be carried out only on non-electrified sections.

3.0 If there are already existing track circuits in the area, these shall be disconnected to
safeguard against false readings being recorded in case of leakage of Block Joints.

4.0 The length of the track required being track circuited should be insulated by means of
Block Joints on either end of the rails. The rail joints in the track-circuited length may or
may not be bonded for purpose of these tests.

5.0 electing a suitable earth, which shall not exceed 5 ohms in resistance, test shall be
carried out.

6.0 A suitable type of milli-volt meter and milli-ammeter shall be used for recording voltages.

7.0 These stray current and rail earth voltage measurements shall be recorded in accordance
with the diagram for measurements indicated below:

FIG. 1 Measurement of Stray Current

Note: For measurement of stray current set up the circuit as shown above and measure
the current simultaneously.

FIG.2 Measurement of Rail-Earth Voltage

Note: Where 9 ohms, 4 ohms or 2.25 ohms relays are used, use 9 ohms, 4 ohms or 2.25
ohms resistance and measure the voltage once at 'X' and next at 'XV’.

Chapter 17: Train Detection Track Circuits & Axle Counters Page 354 of 535