11
PT UNIT USER MANUAL
APRIL 2023 www.eaton.com.cn
4. PT Protection Settings
4. PT Protection Settings
The PT unit protection settings are designed to be
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 the Navigation buttons below the display (for
PT20/25 style) or using rotary switches on the front of the trip
unit (for PT10 style).
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 unit offers a wide range of settings for Long Delay
Pickup (LDPU or I
r
). This setting ranges from 0.4 to 1.0 and
is expressed as a multiple of the frame’s current rating (In).
The pickup value for Long Delay is 105% to 115% of the
calculated value to ensure that the circuit breaker can carry
the full rating of (I
r
), without tripping.
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
r
. All times are referenced from the
top of the tolerance band, ensuring that the time never
exceeds that maximum setting. When an I
4
t slope is selected,
an overload creates a very long-time delay which could
exceed breaker ratings. Therefore, when a time delay above
seven seconds is selected, seven seconds will be used
instead.
If a long delay causes the circuit breaker to trip,
•
For PT10, the “LONG” indicator will blink.
•
For PT20/25, the “LONG” indicator will blink. The “LONG
DELAY” message will be displayed if auxiliary power is
present.
4.1.1 Long Delay Slope Selection
The I
2
t settings is the factory default curve for long delay.
The curve can be changed using the display and navigation
buttons to several alternative curves to better match the
requirements for protection and coordination. The PT 10 only
support I
2
t.
•
I
0.5
t - Slightly inverse time curve
•
It
- Moderately inverse time curve
•
I
2
t - Inverse time current curve, used in standard
distribution protection (factory default)
•
I
4
t - Extremely inverse time current curve, a steep
protective slope for coordination with fuses or for special
type of loads.
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 display
and Navigation buttons or using the Power TRIP Protection
Manager 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.
4.2 Short Delay Pickup and Time Settings
Settings for Short Delay Pickup (SDPU or I
sd
) are expressed
as multiples ranging from 1.5 to 10 for the long delay pickup
current setting (I
r
).
The short delay time (t
sd
) is selected in conjunction with
one of two short delay slopes, flat, or I2 t. There are six
settings for the flat curve of PT10, ranging from 0.05 seconds
(minimum time) to 0.5 seconds, and four settings for the I
2
t
inverse time curve, ranging from 0.1 seconds (minimum time)
to 0.5 seconds.
The I
2
t inverse time curve will provide a longer time delay
for currents below eight times I
r
as compared with a flat
response curve. For currents greater than eight times I
r
, the
I
2
t response flattens out to the flat response.
If a short delay causes the circuit breaker to trip,
•
For PT10, the “SHORT” indicator will blink.
•
For PT20/25, the “SHORT” indicator will blink.
The “SHORT DELAY” message will be displayed if auxiliary
power is present.
The Zone Selective Interlocking (ZSI) feature may affect the
tripping times for the short delay protective function. Please
refer to the section on ZSI.
4.3 Instantaneous Pickup Settin
The instantaneous (Ii) setting is expressed as multiples
ranging from 2 to 15 of the In value or can be set to “OFF”.
The instantaneous protection trips the breaker with no
intentional time delay.
