Trip LED
The Trip LED is illuminated upon any trip condition. It is also
a real-time display and incorporates the circuit breaker’s 52b
auxiliary switch (also called MCR switch) input for its logic.
Pushing the Reset pushbutton or closing the circuit breaker will
clear this LED.
Making current release (MCR)
All trip units styles have a making current release function.
This safety feature prevents the circuit breaker from being
closed and latched-in on a faulted circuit. The NRX NF Frame is
equipped with a nonadjustable release that is preset to pick up
at a peak current of 45,000A. The release level of the RF Frame
is preset to 36,000A for 1600A frame ratings, 56,000A for
2000A and 2500A frame ratings, and 90,000A for 4000A frame
ratings. The level is set by the sensors, frame module, and the
trip unit of the circuit breaker.
The MCR is enabled only for the first two cycles following the
initial circuit breaker closing operation. The MCR circuit will trip
the circuit breaker instantaneously with no intentional delay and
flash the instantaneous (INST) red LED.
High instantaneous
All Series NRX NF frame modules have a high instantaneous
withstand trip feature. Some Series NRX RF frame modules
will have the high instantaneous feature if specified.
This element is always active even when the customer
instantaneous adjustment is set to the OFF position. The high
instantaneous is a separate analog peak detecting circuit that
is set in the frame rating module of the circuit breaker. It will
initiate a trip at a current peak set to match the withstand rating
of the circuit breaker frame. A trip from this feature will be
indicated by flashing the red instantaneous (INST) LED. For
additional information regarding high instantaneous trip levels,
consult the time current curves for the R-Frame breaker located
in publication AD0130100SE.
Ground current sensing schemes
Depending upon the installation requirements, alternative
ground fault sensing schemes may be dictated. The Digitrip
1150 trip units can accommodate one of three different
schemes of sensing.
Ground fault alarm
A ground fault alarm is one of many possible programmable
alarms and can provide an early warning of a ground fault
condition through an alarm LED. In addition, this trip unit can
be programmed to energize an alarm relay upon this condition.
The alarm relay will reset automatically if the ground current is
less than the Ground Alarm Pickup setting.
The Digitrip 1150 provides a greater flexibility in the use of
ground current alarms. If the Ground Alarm option has been
enabled on the LSIA, RLSIA, LSIG, or RLSIG style trip units,
a red Alarm LED will indicate the presence of ground current
when it is in excess of the Ground Alarm setting. See
Table
4
for the specifications on all settings for all of the alarms. A
programmed alarm relay (Relay 1 or 2) will be energized when
the ground current continuously exceeds the ground alarm
setting for a time in excess of 0.1 second. The alarm relay will
reset automatically if the ground current reduces to a value less
than the ground fault pickup setting.
Ground fault trip alarm
On LSIG and RLSIG style trip units, Relay 1 and Relay 2 can be
programmed as a trip relay to indicate when the circuit breaker
trips on a ground fault. You must then push the Reset button in
order to reset the relay contact.
Residual ground current sensing
Residual sensing is the standard mode of ground fault sensing
in Series NRX circuit breakers. This mode uses one current
sensor on each phase conductor and one on the neutral for a
four-wire system. If the system neutral is grounded, but no
phase to neutral loads are used, the Digitrip trip unit includes
all of the components necessary for ground fault protection.
This mode of sensing vectorially sums the outputs of the three
or four individual current sensors. If the vectorial sum is zero,
then no ground fault exists. Residual ground fault sensing
features are adaptable to main and feeder circuit breaker
applications. If an external neutral sensor is used with reverse
feed breaker applications, the proper polarity of the neutral
needs to be considered.
•
CAUTION
ALWAYS OBSERVE THE POLARITY MARKINGS ON THE INSTALLATION
DRAWINGS. IF THE NEUTRAL SENSOR CONNECTIONS ARE
INCORRECT, A NUISANCE TRIP MAY OCCUR.
To ensure correct ground fault equipment performance and
compliance, conduct field testing as required to comply with
country or regional requirements.
Source ground sensing
The ground return method is usually applied when ground fault
protection is desired only on the main circuit breaker in a simple
radial system. This method is also applicable to double-ended
systems where a mid-point grounding electrode is employed.
For this mode of sensing, a single current sensor mounted on
the equipment-bonding jumper will directly measure the total
ground current flowing in the grounding electrode conductor.
Applying the source ground jumper will enable this protection.
ote:
N
When using a Communication Module (see Section 14:
Communications), the enabling of source ground mode is done via the
position of the jumper located on this module.
Zero sequence sensing
Zero sequence sensing, also referred to as vectorial
summation, is applicable to mains, feeders, and special
schemes involving zone protection.
17
EATON
www.eaton.com
Effective September 2013
Instructional Leaflet IL01301064E
Operating Manual for Series NRX
Digitrip Trip Units 1150 / 1150i
