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Magnum PXR applications
MAGNUM PXR PRODUCT GUIDE
PA013006EN September 2022 www.eaton.com
5
ZSI testing
The Zone Selective Interlocking (ZSI) functions in conjunc-
tion with the Short Delay and Ground Fault protection
functions. ZSI provides the fastest possible tripping for
faults within the zone of protection of the circuit breaker
and provides positive coordination among all circuit break-
ers in the system (mains, ties, feeders, and downstream
circuit breakers).
When ZSI is enabled and a fault occurs, all circuit breakers
that see the fault current will send a signal upstream that
they “see” the fault. When the fault current is above the
pickup level of the ground fault or the short delay settings
the circuit breaker will check its input to check if anyone
below it has sent a restraining signal. If there is an input
signal the circuit breaker will follow its normal time delay
waiting for the downstream breaker to clear the fault. If
there is no input signal, and after a double check of the
signal the PXR breaker will immediately trip since it is the
closest circuit breaker to the fault.
The ZSI is wired using a set of three wires labeled Zone
In (ZI), Zone Out (ZO), and Zone Common (ZC) on the
secondary terminals above the circuit breaker. These
signals are compatible with all Eaton circuit breakers
which have the ZSI function. The zone out signal is sent
whenever the ground fault pickup is exceeded or when
the short delay pickup value of 2 x (I
r
) is exceeded. This
provides maximum selectivity for coordination with larger
upstream circuit breakers.
The PXR trip unit display provides unique new features
to help provide confidence that ZSI is enabled, properly
wired, and help test ZSI. The display of the trip unit will
show the letters ZSI on the bottom when ZSI is enabled.
When there is a ZSI input signal detected on the input
terminal the display of the PXR trip unit will show a check-
mark at the bottom next to the letters ZSI. The check mark
will remain on the display until the RESET pushbutton
pushed to clear it.
The following figure shows an example of the Feeder
11 breaker being tested. At the start of a test, press the
RESET pushbutton on all trip units, and all trip units will
start off with the checkmark cleared.
Then Feeder 11 is tested with 4000A of secondary injec-
tion current to simulate a fault above its Short Delay
pickup setting. Feeder 11 shows a checkmark because it is
self-interlocked. Main 1 breaker shows a checkmark, so it
has received the ZSI input signal.
Feeders 12 and 13 are in the same zone as Feeder 11 and
should not see the ZSI input signal. Feeder 12 will not
show a checkmark, which is correct. But Feeder 13 shows
a checkmark. Further inspection will find that Feeder 13
has its input and output signals wired incorrectly.
Additional information on ZSI can be found in the Eaton
application note AP02602002EN.
Figure 77. ZSI test example