Trip Units — Power+™
(cont.)
13
Operation of Power+™ Trip Units
Block diagram of Power+ trip unit
Power+ trip units have a variety of standard and optional
functions. The block diagram shows a fully configured
Power+ trip unit with ground-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 preset conditions produces a
A B C N
Phases
A B C N
Phases
Currents
Phase
Optional
Neutral Current
Rating
Plug
Fault
(Opt)
Ground
Breaker Mounted
Current Sensors
Auxiliary Contact
(Microswitch)
Target
Module
(Optional)
Bell Alarm
with or w/o
Lockout
A/D Converter
Fault
Fault
T
rip Logic
Power+
Trip Unit
T
rip Actuator
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
actuator’s permanent magnet, and allows a spring to unseal
the magnet and trip the breaker.
The bell alarm contacts operate only as a result of an over-
load, short circuit or ground fault 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 multiples 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, 0.5-1.1X, with four
delay bands.
• Adjustable Instantaneous (I) Pickup, up to 15X (see table
21.1 on page 21 for applicable ranges).
Options
• Overload, Short Circuit, and Ground Fault local trip indi-
cators with overload pickup warning and trip unit health
monitor.
• Adjustable Short-Time (S) Pickup, 1.5-9.0C, and delay (3
bands) with I
2
t IN/OUT selection.
• Adjustable Ground Fault (G) Pickup, 0.2-0.6S*, and delay
(3 bands) with I
2
t IN/OUT selection.
• Upgradeable Ground Fault function with use of appropri-
ate ground fault rating plug.
* Maximum ground fault setting is limited to 1200 amperes.
