1 Function
1.1 General information
PXR Electronic trip unit
01/21 MN012005EN
www.eaton.com
9
1 Function
1.1 General information
The subsystem of the new NZM circuit breakers (the NZM2, NZM3 and
NZM4 series) consists of current sensors and a trip actuator in conjunction
with the PXR (Power Xpert Release) electronic trip. The electronic trip units
PXR10, PXR20 and PXR25 in particular ensure the protection function of the
circuit breaker.
In addition to its main function (= protection), the PXR electronic trip unit
makes it possible
•
to check the protection functions of the circuit breaker
(and to log them using the PXPM software),
•
to access the circuit breaker information,
•
and to adjust the circuit breaker settings.
1.2 Technical background
The PXR trip unit analyzes signals transmitted by Rogowski current sensors.
As soon as the current and/or time-delay thresholds are exceeded, the PXR
trip unit will cause the circuit breaker to trip.
The automatic overload and short-circuit tripping characteristics for a given
circuit breaker depend on
•
the specific PXR trip unit version,
•
the rated operational current I
n
,
•
and the protection settings selected by the user.
The current protection functions do not require any external control voltage.
The PXR trip unit consists of a micro-controller module that performs rms
current measurements as well as calculations for the protection functions.
It shall not be removed or replaced.
The current sensors are integrated in the circuit breaker and consist of two
coils per phase: an iron-core coil (for self-supply) and a Rogowski coil for
current measurement.
As soon as a current flows through the circuit breaker, the iron-core coil will
generate a secondary current that supplies the PXR trip unit. At the same
time, the Rogowski coil emits signals that make it possible to determine the
current flowing through the circuit breaker.
The mechanical action required to initiate the tripping of the NZM circuit
breaker is carried out by means of a low-energy trip element. This trip
element is an integral part of the circuit breaker mechanism. This also
includes a toggle lever for manual “opening” and “closing”.
