Section 6: Programming Settings
Protection Settings
Current Slope Selection
Before placing any circuit breaker in operation, set each trip
unit protection setting to the values specified by the engineer
responsible for the installation. Each setting is programmed
and saved using the front panel pushbuttons. Some of the
settings are interdependent such as adjusting the LONG PU
(Ir) rating which will indirectly affect the SHORT PU value.
Therefore, always verify the settings after programming by
entering View setpoints submenu and scroll through the
saved settings.
The installed rating plug establishes the maximum continuous
current rating of the circuit breaker (I
n
). Instantaneous and
ground current settings are defined in multiples of (I
n
).
All Digitrip 1150 style trip units offer the
I
2
t
curve slope as
the standard factory default. The ANSI IEEE protective relay
curve selection is also possible for style trip units for UL/ANSI
applications. The curves accurately follow the IEEE Inverse-
Time characteristic equations. Curve shapes of Moderately
Inverse, Very Inverse, or Extremely Inverse are available. Each
of these curve shapes have a Pickup and Time Dial selection
to position the curve. The short delay function is included with
the IEEE curves.
All Digitrip 1150i style trip units offer the
I
2
t
curve slope as
the standard factory default. The IEC protective relay curve
selection is also possible for these styles of trip units. The IEC
curve type accurately follows the IEC protective relay curve
equations. The curve shapes of IEC-A (normal inverse), IEC-B
(very inverse), and IEC-C (extremely inverse) are available. Each
of these curve shapes have a PICKUP and Time Dial selection
to position the curve. The short delay function is included with
the IEC curves.
All Digitrip 1150 and 1150i style trip units offer the I
4
t curve
slope. This curve option has a very steep protective slope for
coordination with fuses or for special types of loads.
Long Delay Pickup Setting
The Digitrip 1150 offers a wide range of settings for long delay
pickup. The setting, called (
I
r
), is expressed as a multiple
ranging from 50% to 100% of the current (I
n
) value. The
available settings can be set in steps of 5% between that
range.
ote:
N
The nominal current pick-up value for Long Delay is 110% of the
setting. The +/-10% tolerance is then centered around this value. This
is done to ensure that the circuit breaker can carry the full rating of (I
r
),
if desired and programmed that way, without tripping.
Long Delay Time Setting
The long delay time settings for an I
2
t slope, as illustrated in
Figure 14
, range from 2 to 24 seconds. For the I
4
t slope, the
settings range from 1 to 5 seconds. These settings represent
the total clearing times when the current value equals six times
(I
r
)
. All times are referenced from the top of the tolerance
band, ensuring that the time never exceeds that maximum
setting.
Figure 14. Long Delay Time Setting Bands for I
2
t settings
Long Time Thermal Memory
In addition to the standard Long Delay Protection element,
trip units using LONG SLOPE settings of I
2
t or I
4
t also have a
Long Time Memory (LTM) function, which protects load circuits
from the effects of repeated overload conditions. If a circuit
breaker is closed soon after a long delay trip, and the current
again exceeds the long delay setting, (
I
r
), the LTM automatically
reduces the time to trip to allow for the fact that the load
circuit temperature is already higher than normal because of
the prior overload condition. Each time the overload condition
is repeated, the LTM causes the circuit breaker to trip in a
progressively shorter time. When the load current returns to
normal, the LTM begins to reset; after about ten minutes it
will have reset fully, so the next long delay trip time will again
correspond to the setting value. In certain applications and
field testing, it may be desirable to disable the LTM function by
disabling this function in program settings.
ote:
N
The action of the Long time Thermal Memory (LTM) must be
considered when performing multiple long delay time tests .
Short Delay Pickup Settings
The available short delay current settings range from 2 to 10
times (
I
r
). The settings have a step of 0.5 times in the range
limits allowing for maximum protection and coordination
capability. The pickup is nominally in the center of the curve
band with a +/- tolerance from that point.
ote:
N
(Ir) is the long delay pickup current setting times the
(I
n
)
rating
plug value.
24
EATON
www.eaton.com
Effective September 2013
Instructional Leaflet IL01301064E
Operating Manual for Series NRX
Digitrip Trip Units 1150 / 1150i
Available Time
Setting Range
At 6 times Ir
6 x Ir
24 s.
2 s.
Ir
110% Ir
Time
Current in multiples of Ir
