Effective 11/2003
Page 17
I.L. 66A7535H02
up is exceeded or if the short delay pickup is exceeded or
if the value of 2 x (
I
r) is exceeded. Zone Selective Inter-
locking provides the fastest possible tripping for faults
within the zone of protection of the breaker and yet also
provides positive coordination among all breakers in the
system (mains, ties, feeders, and downstream breakers)
to limit a power outage to only the affected parts of the
system. When Zone Interlocking is employed, a fault
within the zone of protection of the breaker will cause the
Digitrip 1150V to:
•
Trip the affected breaker immediately and, at the same
time
•
Issue a signal to upstream Digitrip units to restrain from
tripping immediately. The restraining signal causes the
upstream breakers to follow their set coordination times,
so that the service is only locally disrupted while the
fault is cleared in the shortest time possible.
For an example of how Zone Selective Interlocking may be
used, see Appendix A of this Instructional Leaflet.
3.4 VT and PT Module
NOTE:
The user must initially program via the Program/
Figure 3.2 Digitrip 1150V Trip Unit
Figure 3.3 Digitrip 1150Vi Trip Unit
Voltage Sub Menu the voltage primary and voltage second-
ary values that reflects the external voltage transformers
(VTs) that he will be using. The default values set at the
factory are: Voltage Primary = 4800V and Voltage Second-
ary = 120V. This, along with the frequency setting of 50 or
60 Hertz, are required for the Digitrip to properly present
the current voltage, power and energy values.
A PT (Potential Transformer) Module (Style #70C1271G01)
is internally mounted in the breaker
(See Figure 3.4)
and
wired to the breaker’s secondary contacts B-16 (phase A),
B-17 (phase B) and B-18 (phase C). It is set tp to receive a
typical 120VAC secondary input from the customer’s VTs.
The module further reduces the signal for the Digitrip
1150V to calculate voltage, power, energy and related data.
The PT module is a three phase, three wire input, three
wire output step down transformer wired
wye to wye
.
The power (and energy) metering and protection values will
be positive if the polarity of the current sensors and VTs
are wired per Appendix C and if the power is from top to
bottom of the circuit breaker. If the breaker hookup is
opposite or the current sensors and VTs are different from
how they appear in Appendix C, the value may be shown
as reverse power. The value, however, can be read as an
absolute value by disabling a setting located in the System
Menu labeled
Rev Power Sensing
.
