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New generation IZM97, 99 low voltage air circuit breaker instruction manual
MN013010EN February 2020 www.eaton.com.cn
Section 3: Circuit breaker description and operation
Figure 3-9 Installed PXR trip unit
3-4 Electronic tripping system
Series IZM9 circuit breakers use a three-part tripping sys-
tem:
• Microprocessor-based trip unit connected to a frame rat-
ing module;
• Rogowski coil type current sensors; and
• Trip actuator.
All three parts of the tripping unit are discussed here in
general. For detailed information pertaining to the different
available trip unit models and other breaker or accessory
information, refer to PXR release instruction leaflet.
See important frame rating module information on next
page regarding the tripping system.
3-4.1 Microprocessor-based trip unit
Series IZM97, 99 circuit breakers utilize the PXR family of
electronic trip units whose main features are summarized in
Table 3.1.
The electronic trip units are self-powered devices. The pro-
tection settings can be set from the front panel. When the
circuit breaker is closed, no external power is required to
operate their protective systems. Current signal levels and
the control power are derived from the current sensors. All
trip units are true RMS current sensing devices.
A functional local test of the trip unit’s primary electronic cir-
cuitry and the circuit breaker’s mechanical tripping action can
be performed through the trip unit’s USB receptacle.
Table 3.1 Series PXR trip units.
Functions
PXR 20
PXR 25
LSIG protection
Yes
Yes
Disable (I)
Yes
Yes
GF protection
Option
Option
GF alarm
Option
Option
Display
Yes
Yes
Programmable
No
No
Current metering
Yes
Yes
Power/energy metering
No
Yes
Power quality metering
No
No
Communication
Yes
Yes
3-4.2 Rating plug
A rating plug is not required with PXR trip units. See frame
rating module description.
3-4.3 Current sensors
Rogowski coil type current sensors are installed on the
load terminals at the bottom rear of the circuit breaker. The
sensors furnish the trip unit with a signal and the energy
required to trip the circuit breaker.
An external neutral current sensor is available for customer
installation, and must be ordered separately.
3-4.4 Frame rating module
The PXR frame rating module is mounted just behind the trip
unit and stores data related to the breaker’s ratings (includ-
ing the maximum continuous RMS current), manufacturing
information, and health of the breaker frame.
The interchangeable trip unit attaches to the permanent
frame rating module. Since the PXR trip unit no longer
requires a fixed type rating plug, the continuous current (In)
rating is factory programmed in the frame rating module.
The programmed value of I
n
is shown on the trip unit’s
LCD display and printed on the Battery cover at the lower
right corner of the trip unit. The In rating displayed and pro-
grammed will be equal to or less than the breaker frame’s
maximum rated current as listed on the nameplate.
The breaker’s I
n
rating can be re-programmed by interfacing
with the USB port on the trip unit. Please contact your Eaton
sales representative for details on proper re-programming of
the trip unit.
