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4. PT Protection Settings
4. PT Protection Settings
The PT trip unit protection settings are designed to be
easily customized to any application. Settings for long
delay pickup, long delay time, short delay pickup, short
delay time, instantaneous pickup, ground fault pickup,
and ground fault time are all independently configurable.
These functions are set using rotary switches on the front
of the trip unit.
Please refer to Table 2 for a detailed list of the
configurable setting values.
Before placing any circuit breaker in operation, set each
trip unit protection setting to the values specified by the
engineer responsible for the installation.
4.1 Long Delay Pickup and Time Setting
The PT trip unit offers a wide range of settings for Long
Delay Pickup (LDPU or I
). This setting ranges from 0.4 to
r
1.0 and is expressed as a multiple of the frame's current
rating (I
). The pickup value for Long Delay is 105% to
n
115% of the calculated value to ensure that the circuit
breaker can carry the full rating of (I
The long delay time settings range from 0.5 to 24
seconds. They represent the total clearing times when the
current value equals six times I
from the top of the tolerance band, ensuring that the time
never exceeds that maximum setting.
If a long delay causes the circuit breaker to trip, the
"LONG" indicator will blink.
4.1.1 Long Delay Slope Selection
The I
t setting is the factory default curve for long delay.
2
I
t
- Inverse time current curve, used in standard
2
•
distribution protection (factory default)
4.1.2 Long Delay Thermal Memory
In addition to the standard Long Delay protection, a Long
Time Memory (LTM) function is supported by the trip unit.
This protects load circuits from the effects of repeated
overload conditions. LTM is configured using the Power
Trip Management (PTM) software.
As an example, if a circuit breaker is closed soon after a
Long Delay trip, and the current again exceeds the Long
Delay setting (Ir), the LTM automatically reduces the
time to trip to allow for the fact that the load conductor
temperature is already higher than normal because of the
prior overload condition. Each time the overload condition
is repeated, the LTM causes the circuit breaker to trip
in a progressively shorter time. When the load current
returns to normal, the LTM begins to reset (after about
ten minutes it will have reset fully) so the next long delay
trip time will again correspond to the setting value. It is
recommended to disable the LTM in certain applications
and field tests.
6
PT 10 TrIP UnIT User ManUal Power TrIP (PT) UnITs MN013021EN January 2024 www.eaton.com
), without tripping.
r
. All times are referenced
r
4.2 Short Delay Pickup and Time Settings
Settings for Short Delay Pickup (SDPU or I
expressed as multiples ranging from 1.5 to 10 for the long
delay pickup current setting (I
The short delay time (tsd) is selected in conjunction with
one of two short delay slopes, flat, or I
settings for the flat curve of PT 10, ranging from 0.05
seconds (minimum time) to 0.5 seconds
settings for the I
t inverse time curve, ranging from 0.1
2
seconds (minimum time) to 0.5 seconds.
The I
t response curve will provide a longer time delay
2
for currents below eight times I
response curve. For currents greater than eight times I
the I
t response flattens out to the flat response.
2
If a short delay causes the circuit breaker to trip, the
"SHORT" indicator will blink.
0.05, 0.1, 0.2, 0.3, 0.5
0.05s: nominal clear time is less than or equal to 0.08s;
0.1s: trip time is 0.06s to 0.11s;
0.2s: trip time is 0.14s to 0.2s;
0.3s: trip time is 0.21s to 0.3s;
0.5s: trip time is 0.35s to 0.5s;
4.3 Instantaneous Pickup Setting
The instantaneous (I
) setting is expressed as multiples
i
ranging from 2 to 15 of the I
The instantaneous protection trips the breaker with no
intentional time delay.
4.4 Ground Fault Settings
When the PT 10 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.
If not needed, the Ground Fault function can be switched
off using the rotary switch on the trip unit front face.
4.4.1 Ground Fault Pickup
The PT 10 trip 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.
The ground fault detection pickup level with an alarm
only action may be selected using the rotary switch.
With the alarm-only selection, four levels of pickup
level are available. This set of pickup levels is labeled
"Alarm" .
) are
sd
).
r
t. There are six
2
, and four
as compared with a flat
r
value or can be set to "OFF" .
n
,
r
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