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4. PT Protection Settings
If a circuit breaker trips instantaneously,
•
For PT10, the "INST" indicator will blink.
•
For PT20/25, the "INST" indicator will blink. The "INST
TRIP" message will be displayed if auxiliary power is
present.
4.4 Ground Fault Settings
When the trip unit includes ground fault protection features,
the distribution system characteristics (such as system
grounding, number of sources, and number and location
of ground points) must be considered along with the
manner and location in which the circuit breaker is applied
to the system. To ensure correct ground fault equipment
performance and compliance, you must conduct the
field testing required to comply with country or regional
requirements.
4.4.1 Ground Fault Pickup
The PT unit provides flexibility in detecting and acting on
ground currents. A ground fault alarm can provide an early
warning of a ground fault condition and a ground fault trip
can provide protection under these conditions. A trip unit can
be set to alarm, trip or OFF for a ground fault.
1.The ground detection may be turned off by setting the
rotary switch to "OFF"
2.With the alarm-only selection, four pickup levels are
available. This set of pickup levels is labeled "Alarm".
3.The ground fault detection with an action of trip may also
be selected. With detect and trip selection, this set of pickup
levels is labeled "Trip".
If a ground fault causes the circuit breaker to trip,
•
For PT10, the "GND" indicator will blink.
•
For PT20/25, the "GND" indicator will blink.
The "GND TRIP" message will be displayed if auxiliary power is
present.
Note: Your application may require ground fault protection.
Please consider NEC and/or applicable codes to determine
required mode of operation ("OFF", "Alarm", or "Trip")
4.4.2 Ground Fault Time
The PT unit provides selection for two different ground fault
slopes: a fixed time (flat) or I
slope should be chosen to match selective coordination
needs. The I
t response provides a longer time delay for
2
current below 0.625 x I
than the fixed time (flat) response.
n
PT10
The time delay and slope are selected on the corresponding
12
PT UNIT USER MANUAL APRIL 2023 www.eaton.com.cn
t inverse time response. The
2
rotary switch (PT10 rotary switch type). The I
selections are indicated with an asterisk (*) while the fixed
time (flat) response time selections are indicated without an
asterisk. Both have a range from 0.1 seconds to 0.5 seconds.
PT20/25
For PT20/25 units, Navigation buttons below the display can
be used to make selections on the display.
4.4.3 Ground Fault Thermal Memory
In addition to standard ground fault protection, the PT unit
also has a ground fault memory function that serves to
protect loads in the event of a sputtering arc to ground.
Without this function, the ground fault protection timer resets
each time the arc goes out, so that a sputtering ground
fault may not trip the circuit breaker. With the ground fault
memory function, the trip unit "remembers" the sputtering
ground current. The time delay due to the memory decays
with time, the time interval equals 6.25 times the ground fault
time. For example, with a 0.4 second setting, the function will
reset in 2.5 seconds.
•
The thermal memory function can be enabled or
disabled on PT20/25 using the display and navigation
buttons or by using the PTM software.
•
The thermal memory function can be enabled or
disabled on PT10 using the PTM software.
4.4.4 Ground Fault Relay
If the Ground Fault Alarm option is selected on the LSIG style
trip units, a red ground Alarm indicator will illuminate to show
the presence of ground current in excess of the Ground
Alarm setting. The trip unit will activate an alarm relay upon
the conditions if auxiliary power is present and the PT25 trip
unit is selected with the corresponding relay configured for
the ground fault alarm option. The indicator and relay will
reset automatically when the ground current reduces to a
value less than the ground fault pickup setting.
If the Ground Fault Trip option is selected, the alarm relay
can be configured to activate when the circuit breaker has
tripped on a ground fault. You must then push the "RESET"
button in order to reset the relay contact.
4.5 Ground Fault Sensing
The PT unit provides for three modes of sensing to detect
ground fault currents: Residual, Source Ground, and Zero
Sequence. More detailed descriptions, refer to the ground
methods in Figure 14 below.
The ground sensing mode (Residual or Source/Zero Seq) is
selected using the display and navigation buttons or by using
the PTM software.
Neutral protection is provided independent of the Ground
Fault function.
t response time
2
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