Eaton PXR10, PXR20, PXR25 Electronic trip unit Power Xpert Release PXR for NZM... circuit breakers

Function

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.

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 In,

• 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”.

Overload indicator

PXR10. PXR20

The PXR10 and PXR20 trip units are equipped with an orange overload LED

for load and overload warnings, which are triggered at 85 % (LED on) and

105 % (LED flashing) of Ir, respectively. Once the current has dropped below

the threshold again, the indicator will switch off or return to its previous

state. The threshold values are fixed.

PXR25

On the PXR25 trip unit, the threshold values for load and overload warnings

can be adjusted via the LCD display.

Tamper-proof cover

The NZM digital circuit breaker is equipped with a transparent plastic cover.

When this cover is closed, the settings can be displayed but not changed. In

order to comply with the applicable tamper-proof requirements, any

unauthorized changes to the settings can be prevented by inserting a

standard seal into the safety hole.

On the PXR25 trip unit, the protection settings are additionally password

protected. The PXR25 trip unit cover features openings above the up and

down arrow keys. This makes it possible to view the “screensaver” display

and the values it depicts. The enter button cannot be pressed while the cover

is closed. It is therefore not possible to switch from the screensaver to the

main menu while the cover is closed.