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WL Circuit Breaker
Electronic Trip Unit (ETU)
Electronic trip units (ETUs)
Power system protection is necessary to treat common types of
abnormal occurrences, such as overloads or faults that can lead
to electrical power system failure.
The methods for detecting and clearing such abnormalities
and restore to normal operation is an engineered technique.
Adequate protection requires constant measurements of certain
system quantities, such as voltages and currents, comparing
those system quantities, or some combination of the quantities,
to a threshold setting computed by a systems engineer and
set into an electronic trip unit like those available on the WL
breakers. It's equally important for power system protection
to perform under normal operating conditions. If the above
thresholds are set too low the power may be interrupted
unnecessarily causing loss of productivity or safety provisions.
The WL circuit breaker offers a practical means of setting
power system protection through vast selectivity available in
its Electronic Trip Unit (ETU). WL ETUs have a wide range of
protective settings for implementing simple or complex
coordination schemes and configuring reliable system protection.
ETU enhanced features
• Extended Instantaneous Protection (EIP): Allows the entire
range of WL ampacities to be applied at the withstand rating
of the breaker with minus 0% tolerance; that means no
instantaneous override whatsoever. EIP further enables the
circuit breaker to be applied up to the full interrupting rating
of the breaker on systems where the available fault current
exceeds the withstand rating, even with LS-only trip units.
• Dynamic Arc-Flash Sentry (DAS): Allows you the ability to
execute a faster coordinated trip condition should an arc
fault event occur while personnel are within the arc flash
boundary. When the presence of personnel is no longer in
the arc flash boundary, DAS will default back to maintaining
your selective trip coordination through time delay functions.
This is like toggling between two trip units on one breaker.
DAS can be activated by a simple contact closer, so a wide
range of activation devices can be used to enable DAS.
4
• Selectable I
t: ETU745 and 776 make it possible to switch
2
4
over from an I
t to an I
t inverse-time function for overload
protection. This selectivity increases optimization of
coordinated overload protection when overload fuse
protection is also provided.
ETU basic functions
Long-time trip
The long-time delay adjustment is used to set the tripping delay
of the circuit breaker based on the magnitude of the overcurrent
condition (6 times l
). For example if the rating plug is 2000
r
8
Courtesy of NationalSwitchgear.com
amps and the long-time delay is set to 10 seconds, a fault current
of 12,000 amps (6 x 2000) will cause the breaker to trip after
10 seconds. Long-time is an inverse of I
means the higher the current, the shorter the time the circuit
breaker will remain closed. An Alarm LED indicator will flash
during the delay period and a separate "Trip L" indicator may
turn on if the breaker trips on long-time function.
Short-time trip
The short-time pickup adjustment is used to set the level of
high current the breaker will carry for a short period of time
without tripping. This adjustment is set in multiples of the
value of the rating plug (Ir). Together with the short-time delay,
this adjustment allows downstream breakers time to clear short
circuit faults without tripping upstream breakers. Short-time
delay is used to set the time interval the breaker will wait before
responding to the current value selected by short-time pickup.
There are two modes of operation: fixed and I
has the characteristic of being inversely proportional to the
square of the magnitude of the current. This means higher
overcurrent conditions have shorter delays. An Alarm LED
indicator may flash during the delay period and a separate
"Trip S" indicator will turn on if the breaker trips on short-
time function.
Instantaneous trip
The instantaneous pickup adjustment is used to set the current
level at which the breaker will trip without an intentional
time delay. Non-delayed tripping as a result of severe over-
current minimizes potential damage to the electrical system
and equipment.
Ground fault
The ground fault pickup adjustment is used to set the level of
ground current at which circuit interruption will be initiated.
Together with ground fault delay, this adjustment allows
selective tripping between main and feeder or downstream
breakers.
The ground fault delay adjustment is used to set the time interval
(in seconds) the breaker will wait before responding once the
ground fault pickup level has been reached. The available ground
fault delay settings available are: inverse time (I
WL Circuit Breaker Selection and Application Guide
2
t ramp function. This
2
t. The I
2
t delay
2
t) or fixed delay.
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