Page 537 - IRSEM_Main Book

Section 5: Outdoor Signalling Circuits in RE area

22.5.1 Maximum Length of Parallelism

(a) The length of any signalling line circuit must be limited to ensure that the
induced voltage from the traction system does not exceed 400 Volts under
normal conditions. If necessary, line circuits must be sectionalized. Where line
circuits leave line side enclosures or buildings in different directions, this could
give rise to a continuous circuit of such length that the limits of induced voltage
above could be exceeded. In such cases a sectionalized power supply unit
should be provided for each direction.

(b) The induced voltage in the underground-Unscreened cable shall be
reckoned as 116 Volts/km on single line and 95 Volts/km on Double Line
under normal conditions when the catenary current of 800 amperes for
single line and 1000 amperes for double line.

(c) When such circuits are terminated on relays/equipment their immunity
shall not be less than 400 V AC. Length of feed cable terminated on relay
shall be suitably reduced depending upon its AC immunity.

(d) The length of DC Circuits on Line Relays with unscreened cable shall be
restricted to-

Type of Relay AC immunity Maximum permissible length on*
level in volts
Single Line Double Line

QNA1/QNNA1/QNA1K 1000 2.1 km 2.8 km

K50 B1 170 1.0 km 1.2 km
K50 B1-A2 450 2.1 km 2.8 km

K50 130 750 meters 900 meters
AC Immunized neutral 750 2.1 km 2.8 km
relay (IHC Make)

* Maximum permissible induced voltage is restricted to 400V for human safety
and factor of safety 1.5 has been considered.

Section 6: Signal Feed Circuitry in RE Area

22.6.1 Feeding Distance

Signal feed system shall be of the 110 V 50 Hz type or any approved type.

22.6.2 The distance between the signal control relays and the signal must not exceed
the prescribed limits in electrified zone, measured along the line of way. This
will ensure that the voltage induced in the circuit will be inadequate to
illuminate the lamps, even under the most adverse circumstances and with
one or more earth faults present.

Chapter 22: Requirements Of Signalling in 25 KV AC Electrified Area Page 480 of 535