Power+™ Trip Units
Operation Of Power+ ™ Trip Units
Phases
A B
C N
urrents
ptug
!Optional Neu'b'al Current)
Power+""
Microprocessor
Fault
A B C
N
""''"
Block diagram of Power+ trip unit
Fault
Contact Position Switch
'"With or without lockout
Power+ trip units have a variety of standard and optional
functions. The block diagram shows a fully config ured
Power+ trip unit with g round-fault protection. The current
sensors are special current transformers that provide the trip
unit with its operating power. Interchangeable rating plugs
act as scalars for the outputs of the current sensors, as well
as establish the current rating of individual breakers. When
a four-wire system is used and ground-fault protection is
called for, an external neutral sensor is necessary.
Analog current signals are converted to digital values, and
are measured and compared with established trip settings
in the microprocessor's memory. Any overcurrent or ground
fault condition that exceeds pre-set conditions produce a trip
signal from the microprocessor to the trip actuator. The trip
actuator is a low-energy, positive-action tripping device. The
low-level trip signal counteracts the strength of the actua
tor's permanent magnet, and allows a spring to unseal the
magnet an d trip the breaker.
Both the shunt trip and undervoltage release (UVR) acces
sories also produce trip signals to the trip actuator when
energized. The two bell alarms operate only as a result of an
overcurrent trip condition.
Standard And Optional Protective Functions
Standard and optional protective functions for Power+
trip units are shown below. The breaker settings are pro
grammed in m ultiples of "X" (rating plug amp values). "S"
(current sensor amp rating values). and "C" (the long-time
setting in amps-multiply long-time setting by rating plug
amp rating).
Standard
•
Adjustable Long-Time (L) Pickup, 0.5 - 1.0X, with fou r delay
bands.
•
Adjustable Instantaneous
(I)
Pickup, 1.5 - 1 5X.*
Options
•
Overload, Short Circuit, and Short-Time local trip indicators
with overload pickup warning and health monitors.
•
Adjustable Short-Time (S) Pickup, 1.5 -9.0C, and delay (3
bands) with l2t ON/OFF selection.
•
Adjustable Ground Fault (G) Pickup, 02. 0 - 0.6S, and delay*
(3 bands) with 12t ON/OFF selection and trip indicator.
•
U pgradeable Ground Fault function with use of appropri
ate ground rating plug.
*
Limited by breaker frame size a bove ZOOOA.
9
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