Short Delay Time Setting
As illustrated in
Figure 15
there are two different short delay
slopes: flat and I
2
t. The shape selected depends on the type
of selective coordination chosen. The I
2
t response curve
will provide a longer time delay for currents below 8 x I
r
as
compared with a FLAT response curve.
ote:
N
The I
2
t response for short time is not available if long time is set
for I
4
t, IEEE, or IEC slope curve setting.
The time delay settings range from 0.1 to 0.5 seconds for both
the flat and the I
2
t setting with a resolution setpoint step of
0.05 seconds.. The I
2
t response is applicable to currents less
than eight times the ampere rating of the installed rating plug
(
I
r
). For currents greater than 8 x (
I
r
), the I
2
t response reverts
to the FLAT response. The optional zone selective interlocking
feature will effect the tripping times for the short delay
protective function.
ote:
N
See Section 4: Principles of operation and Appendix A: Zone
Selective Interlocking Examples for more information on zone
interlocking.
Figure 15. Short Delay Time Setting Bands - Flat and I
2
t
Instantaneous Pickup Setting
The
I
i
instantaneous (INST) setting has a range from 2 to 12
times the (I
n
) value in increments of 0.5 resolution. The pickup
is nominally in the center of the curve band with a +/- tolerance
from that point. The instantaneous pickup is based on the plug
(In) rating allowing maximum fault settings based on the frame
rating of the circuit breaker.
Ground Pickup Setting
The ground fault current settings range from 24% to 100% x
(I
n
) in 1% increments. The ANSI/UL models have a maximum
setting of 1200A. The Digitrip 1150i styles with earth protection
have pickup range from 10% to 100% x (I
n
) without a maximum
restriction. External control power is required to ensure Ground
Fault tripping for fault currents at or less than 0.24 per unit.
Ground Time Setting
There is a selection for two different ground fault slopes: a fixed
time (FLAT) or I
2
t response. The shape selected depends on
the type of selective coordination chosen. The I
2
t response will
provide a longer time delay for current below 0.625 x I
n
than
will the FLAT response.
The ground time setting range for both FLAT and I
2
t responses
is 0.1 to 0.5 seconds in increments of 0.05 seconds. For
currents greater than 0.625 x (I
n
), the I
2
t response reverts to the
FLAT response.
ote:
N
See Section 4 and Appendix A on zone interlocking.
In addition to standard ground fault protection, the Digitrip 1150
trip unit also has a ground fault memory function that serves
to protect loads in the event of a sputtering arc to ground.
Without this function, the ground fault protection timer resets
each time the arc goes out, so that a sputtering fault may not
trip the circuit breaker. With the ground fault memory function,
the trip unit “remembers” the sputtering ground current. The
memory decays with time. The decay time interval equals 16
times the time delay setting. The ground fault memory function
resets quickly. For example, the 0.4 second setting the function
will reset in 6.4 second.
Other System Protection Settings
Amp Unbalance
The amp unbalance trip function can be selected in the program
settings submenu. It is set to OFF as a factory default. The
pickup unbalance is adjustable from 5-25%. Once selected,
an associated time delay is adjustable from 0 to 240 seconds.
The setting time tolerance is ±3% or ±0.3 seconds (whichever
is greater). When the difference between the maximum
phase and minimum phase current is higher than the amp
unbalance percent settings will cause the breaker to trip with
an AMPERES OUT OF BALANCE message and red trip LED
illuminated. This function requires external auxiliary power to
the trip unit. To avoid unnecessary operation of this function
at low levels of current, the trip unit requires that the circuit
breaker must be carrying 50% of the Ir rating on at least one
phase before it will trip via amp unbalance.
25
EATON
www.eaton.com
Effective September 2013
Instructional Leaflet IL01301064E
Operating Manual for Series NRX
Digitrip Trip Units 1150 / 1150i
Available Time
Setting Range
With FLAT response
I
2
t slope returns
to FLAT response
at currents higher
than 8 x Ir
Available Time
Setting Range
With I2t
response
8 x Ir.
Time
Current in multiples of Ir
0.5 s.
0.1 s.
0.5 s.
0.1 s.
SDPU x Ir.
