Page 522 - IRSEM_Main Book

Para No. 19.6.1, 21.2.1(b) Annexure: 21-A1

Relays for Railway Signalling

1.0 Relays in General

(a) Relay Working Principle: A relay is an electromagnetic device, which is used for
closing or opening of an electrical circuit. The relay may be classified as Shelf type and
Plug-In Type. Plug-in-type relays which are plugged in to prewired terminal boards. It
works on electromagnetic principle. Each relay has a base electromagnet, armature,
contact spring, contacts, transparent cover, and handle. It works on a low current. A
non-magnetic residual pin is fixed on the inner face of armature, in all relay except
magnetic latch relays. When current is applied through the coil, it sets up a magnetic
flux through the bar magnet, core, L shape heel piece and armature.

2.0 Metal to Carbon Line Relay - Non- AC Immunized Relays

(a) QN1 Style Relay: This is used as internal relay for all control and detection circuit
except in external circuits of AC RE area. It`s specification No-B.R.S. No: 930A.Though
it is immune to 300 Volt AC 50 Hz but only in emergencies can be used in RE area with
protection against AC Interface

(b) QS3 Style Relay: It is sensitive line relay. It works on a low current. It works on 12 V
DC. It`s Specification is B.R.S. 930A.

(c) QB3 relay is biased neutral line Relay: It works on 12 V DC and has a contact
configuration of 4F/2B it is a biased relay. Its Biasing stands good up to 240 Volt DC.
This is confirming to BRS Specification No.930A.

(d) QNN1 Style Relay: This comprises two neutral line relays whose contacts and
magnets are mounted side by side with a common heel piece on a base. These two
relays operate independently to each other and also have equal number of front and
back contacts. It is based on BR specification 960.

3.0 Metal- Carbon - AC Immunised Q- style line relays

(a) AC Immunised DC neutral line Relay: The relay design shall be inherently such that
the immunisation is achieved intrinsically without use of any external means. The
relay shall not make any of its front contacts when 1000 V (r. m. s) of 50 Hz AC is
applied at any instant to the terminals of relay coils. The relay shall not break any of
its back contacts when 300 V (r. m. s) of 50 Hz AC is applied at any instant to the
terminals of relay coils. This is confirming to IRS Specification No. S60 –78. Usage:
these relays are used as interface relays in Electronic Interlocking systems.

(b) QNA1 Relay: The immunisation is achieved by provision of a copper slug on the core
at its armature end. In all other respects, it is similar to QN1.Its Specification is BR
specification no. 931A. Usage: These relays are used as external relays.

(c) QBA1 Relay: This is a DC biased AC immune neutral line relay. A copper slug is
provided on the core for immunisation and a permanent magnet is provided on the
core for Biasing. It does not operate if 20 times of the rated voltage is applied in
reverse direction. It’s specification is BR Specification No. 932 A.

Chapter 21: Relay & Electronic Interlocking Page 465 of 535