Before putting relays into service, remove all blocking
which may have been inserted for the purpose of secur-
ing the parts during shipment, make sure that all mov-
ing parts operate freely, inspect the contacts to see that
they are clean and close properly, and operate the relay
to check the settings and electrical connections.
1. APPLICATION
The TRB Zener tripping unit is an auxiliary device energized
by protective relays to trip circuit breakers in a double trip
relaying scheme. It is suitable for cases where the total trip
current of the two breakers is within the relay contact rating,
usually 30 amperes. The TRB-2 unit can also be used for
isolation of multiple trip paths to one breaker.
2. CONSTRUCTION AND OPERATION
TRB Zener tripping units consists of 50-watt Zener diodes
on brass plates contained within a short metal cage and
mounted on a small molded base. The TRB-2 unit contains
two diode circuits which are completely independent from
each other. These circuits may have only one diode each
or, in the case of 250 Vdc ratings, may each have two di-
odes in series.
!CAUTION
TRB-3 units contain three diodes, two of which have a
common anode terminal and separate cathode terminals.
The third diode is completely independent from the other
two.
TRB-4 units contain four diodes in two completely inde-
pendent circuits. Each circuit has two diodes which have
a common anode terminal and separate cathode termi-
nals.
TheTRBZenertrippingunitisenergizedthroughthecon-
tactsof protective relays as shown in Figure 1. Relay con-
tacts PR trips two breakers through diodes D1 and D2.
However, relay contacts #1 and #2 can energize only
their own related breakers #1 and #2 respectively be-
cause current flow to the adjacent breaker trip coil is
blocked by diodes D1 and D2. Thus relays associated
with each particular breaker are isolated from the other
breaker, yet both breakers can be tripped, without addi-
tional time delay, by the operation of a common relay.
Transient voltages induced into the diode circuits in ex-
cessoftheirreverseblockingratingcanbetoleratedwith-
out damage to the diodes. This feature results from the
zener characteristic which allows current to flow in the re-
verse direction and limits the voltage across the diode.
41-842D
ABB Power T&D Company Inc.
Power Automation and Protection Division
Coral Springs, FL 33065
Type TRB
Zener Tripping Unit
Instruction Leaflet
Effective: January 1997
Supersedes 41-842C Dated May 1992
All possible contingencies which may arise during installation, operation or maintenance, and all details and
variations of this equipment do not purport to be covered by these instructions. If further information is desired
by purchaser regarding this particular installation, operation or maintenance of this equipment, the local ABB
Power T&D Company Inc. representative should be contacted.
(|) Denotes Change Since Previous Issue
Maximum Maximum Zener
One Forward Reverse Reverse Maximum
Sec. Volts Leakage Voltage Zener
Type Rating Diode Rating Drop Micro Amps In Volts Current
at 152 Volts
TRB-2 125Vdc 1N2846 30 Amps 1.5 4 µA 200 ±10% 75 mA
TRB-2 250Vdc 1N2846 30 Amps 3.0 4 µA 400 ±10% 75 mA
TRB-3 125Vdc 1N2846 30 Amps 1.5 4 µA 200 ±10% 75 mA
TRB-4 125Vdc 1N2846 30 Amps 1.5 4 µA 200 ±10% 75 mA
Characteristics and Ratings
Printed in Coral Springs, FL
