CH 17 Stray Current Measurement PDF

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 Elec...

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 530 8.0 These measurements shall be recorded at different periods of the day - one in the morning, one in the afternoon and one in the evening. These tests shall be extended for three days. 9.0 Where stray current/voltages are observed, the length of the Direct Current track circuit shall be cut down so as not to exceed the following limits for each length of Track Circuit: (a) The Rail-Earth voltage as measured across 9 ohms, 4 ohms, or 2.25 ohms shall not exceed 0.1 V. (b) The total stray current as measured shall not exceed 100 mA. Where all track circuits to be installed on the line are less than 100 meters long, the highest acceptable figure of stray current is 10 mA. Chapter 17: Train Detection Track Circuits & Axle Counters Page 355 of 530