TYPE TD-52 RELAY
SILICON
CC.� f?O LLED
RECTIFIER
INTERNAL SCHEMATIC
7621\500
Fig. 2.
Internal Schematic of Type TD-52 Relay with Single Trip
0.212.0
Ampere ICS Units (Relay with Single Trip 1.0
Ampere ICS Units has Identical Wiring Except the ICS
Coils are not Tapped on Terminals 10 and 20, 849A417).
which compensate for the forward voltage drop
through SCR and 02 and zener reference varia
tions.
TELE PHONE RELAY (TR)
The telephone relay (TR) is energized by SCR
at the conclusion of the time delay. The coil is
energized by at least three times pick-up wattage
to insure positive contact operation. The contacts
are made of palladium and are suitable for circuit
breaker trip duty, as proven by many years of ex
perience in other relays. Two sets of transfer con
tacts are provided to give a flexible trip circuit
arrangement.
INDICATING CONTACTOR SWITCH (ICS)
The indicating contactor switch is a small de
operated clapper type device. A magnetic ar
mature, to which leaf-spring mounted contacts are
attached, is attracted to the magnetic core upon
energization of the switch. When the switch closes,
the moving contacts bridge two stationary con
tacts, completing the trip circuit. Also, during this
operation two fingers on the armature deflect a
spring located on the front of the switch, which
I.L. 41-579.3
allows the operation indicator target to drop. The
target is reset from the outside of the case by a
push rod located at the bottom of the case.
The front spring, in addition to holding the
target, provides restraint for the armature and
thus controls the pickup value of the switch.
OPERATION
Operation of the T 0-5 unit occurs when a
silicon controlled rectifier (SCR) switches from a
non-conducting state to a conducting state. In the
non-conducting state, the SCR acts as an opened
switch to prevent energization of the telephone
relay (TR), but in the conducting state acts as a
closed switch to connect the telephone relay to the
de source. To switch the SCR from a non
conducting state to a conducting state requires
that a maximum of 20 microamperes flow in the
gate of the SCR. This current is produced by the
difference in voltage across the capacitor (C) and
the brush of the potentiometer (P).
When de voltage is first applied to the relay,
voltage instantaneously appears across the poten
tiometer brush but is delayed in building up across
the capacitor in accordance with the R-C time
constant of the circuit. As long as the capacitor
voltage is less than the potentiometer brush volt
age, a reverse voltage appears across the diode,
02, and the SCR to keep the silicon controlled
rectifier (SCR) biased off. When the capacitor
voltage reaches the potentiometer brush voltage
plus approximately one volt (forward voltage drop
across SCR and 02), gate current will flow to the
silicon controlled rectifier (SCR). This current
switches the SCR to a conducting state to allow
the telephone relay (TR) to pickup.
The SCR latches on when it switches and can
be reset only by removing voltage from terminals
8 and 9 or terminals 18 and 19. If a trip coil super
visory indicator lamp is used, when the timer is
used with a fault detector to trip a breaker, a
breaker "a" contact must be connected between
terminal 8 andjor terminal 18 of the relay and
negative.
The rate at which the capacitor charges is
determined by the rheostat setting. The charging
3
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