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PXR trip unit and communication modules
Overview of PXR
3
electronic trip units
The Power Xpert Release (PXR) trip
unit, along with current sensors and
a trip actuator, is the subsystem of
a circuit breaker that provides the
protection, monitoring and metering
functions. The PXR analyzes signals
from the current sensors and voltage
connections. If the current level and
time delay settings are exceeded,
then the PXR trip unit will initiate
a trip of the circuit breaker. The
automatic overload and short circuit
tripping characteristics for a specific
circuit breaker are determined by
the current rating and user selected
protection settings. A wide range of
adjustments of the protection allow
the breaker to be coordinated and
adapted to any application. External
control voltage is not required for
current protection functionality.
The PXR protection system consists
of three modules: the frame module,
the trip unit module and the voltage
sensing module (for PXR 25). The
frame module is matched to the
ratings of the circuit breaker and
permanently attached to the circuit
breaker frame. It should not be
removed or exchanged. The trip unit
module is the main body of the trip
unit and mounts on to the frame
module. The trip unit contains a
microcontroller that performs true
rms current sensing measurements
and calculations for protection. It may
be replaced in the field. The voltage
sensing module is attached to the
frame module and provides the low
voltage signals for each of the phases
and neutral (if applicable and wired)
to the trip unit module.
The current sensors are internal to
the circuit breaker frame and consist
of two coils: one coil has an iron
core, and one coil has an air core
(Rogowski coil). As current begins to
flow through the circuit breaker, the
iron core coil generates a secondary
current that powers the trip unit.
At the same time, the air core coil
provides signals that are processed
to measure the current through
the circuit breaker. The mechanical
action required to initiate tripping of
the circuit breaker is provided by a
special low-energy trip actuator.
30
MAGNUM PXR PRODUCT GUIDE PA013006EN September 2022 www.eaton.com
This trip actuator is an integral part of
the circuit breaker mechanism that
enables fast tripping of the circuit
breaker. The trip actuator is automati-
cally reset by the mechanism.
Standards and certifications
The PXR trip units are listed by
Underwriters Laboratories Inc. UL©
for use in Magnum PXR circuit
breakers. All the PXR trip units have
passed the UL 1066, ANSI C37 .90.1,
2, 3 and IEC 60947-2 EMC testing
requirements.
PXR protection settings/
features
A summary of the PXR 20 and PXR
25 features in addition to the list in
tables: Tables 6 and 7.
Long Delay Pickup and Time
•
Setting
Long Delay Slope Selection
•
Long Delay Thermal Memory
•
Short Delay Pickup and Time
•
Settings
Instantaneous Pickup Setting
•
Ground Fault (GF) Setting/Sensing:
•
GF Pickup, GF Time, GF Thermal
Memory, GF ZSI, GF Alarm Relay,
Residual Current Sensing, Source
Ground Sensing, Zero Sequence
Sensing
Making Current Release (MCR)
•
Zone Selective Interlocking (ZSI)
•
Alpha Numeric Dot Matrix digital
•
display
Health Menu
•
Native Modbus RTU commu-
•
nications (optional on PXR 20 /
standard on PXR 25). Optional
Communication Adapter Modules
(CAM) are available for other serial
communication protocols. The DIN
rail mounted CAMs are available
with Ethernet TCP/IP (ECAM) or
with Profibus DP (PCAM).
Maintenance Mode /ARMS
•
(optional on PXR 20 / standard
on PXR 25): The PXR trip units
support Eaton's Arcflash Reduction
Maintenance System, also referred
to as ARMS. When enabled, the
trip unit will trip the breaker with
an accelerated trip time whenever
the configured pickup level is
exceeded. The Maintenance Mode
function operates regardless of
the Instantaneous settings. If
Maintenance Mode causes the
circuit breaker to trip, the "INST"
indicator will be illuminated, and
the "ARMS Trip" message will
be displayed (if auxiliary power is
present).
Figure 33. PXR 20 and 25 trip units
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