13
3. Protection functions
Power XPert® release triP unit for MagnuM PXr circuit breakers
MN013015EN January 2022 www.eaton.com
Table 6. GF source and zero sequence settings.
setting
sg/Zs
ratio
PXr 25 from 0.2 to 1.0 in steps of 0.01
PXr 20 0.2
0.4
0.6
0.8
1.0
1200/1
I
g
= 240
480
720
960
1200
1000/1
I
g
= 200
400
600
800
1000
800/1
I
g
= 160
320
480
640
800
400/1
I
g
= 80
160
240
320
400
400/1
I
g
= 80
160
240
320
400
200/1
I
g
= 40
80
120
160
200
200/1
I
g
= 40
80
120
160
200
100/1
I
g
= 20
40
60
80
100
100/1
I
g
= 20
40
60
80
100
50/1
I
g
= 10
20
30
40
50
50/1
I
g
= 10
20
30
40
50
25/1
I
g
= 5
10
15
20
25
25/1
I
g
= 5
10
15
20
25
10/1
I
g
= 2
4
6
8
10
10/1
I
g
= 2
4
6
8
10
The time delay settings are the same for source ground/zero
sequence as they are for residual sensing.
3.6.3 Ground fault thermal memory
In addition to standard ground fault protection, the PXR trip
unit also has a ground fault thermal memory function that
serves to protect loads in the event of an intermittent or
sputtering arc to ground. Without this function, the ground
fault protection timer resets each time the arc goes out
and the ground fault current is below pickup. Therefore, a
sputtering arc fault may not trip the circuit breaker. With the
ground fault memory function, the trip unit “remembers”
the sputtering ground current. The memory decays with
time when the ground current is below pickup. The reset
time interval equals six times the ground fault time. For
example, with a 0.4 second setting, the function will reset in
2.5 seconds.
3.6.4 Ground fault zone zelective interlocking
In addition to Short Delay phase ZSI, the PXR trip units have
ground fault protection ZSI. The ground protection ZSI can
be enabled or disabled independently of short delay ZSI.
They both work on the same set of wires and perform the
same except for different protection functions. More infor-
mation can be found in Section 3.9 - Zone selective interlock-
ing (ZSI) of this manual.
3.6.5 Ground fault pre-alarm
A unique feature of the PXR trip units is the ability to set a
pre-alarm signal when the level of ground fault current gets
to a desired level. The pre-alarm activate level can be set
from 50% to 100% of the I
g
pickup value. The pre-alarm
notification can also be mapped to the one of the three trip
unit relays.
3.7 Enhanced protection settings
The PXR 25 offers an additional set of functions which can
be used to generate an alarm or trip the breaker. Each has
specific setpoints for pick-up and time delay (minimum 1.0
second). In addition, the actions are configurable to OFF
(default), ALARM, or TRIP. The ranges for each setpoint are
shown in Section 1.4 - Enhanced protection features.
3.7.1 Over voltage
Line-to-line RMS voltages (Vab, Vbc, Vca) are continuously
monitored. If any line-to-line voltage is greater than the
pickup for the time delay, then the configured action will be
taken.
3.7.2 Under voltage
If any line-to-line voltage is less than the pickup for the time
delay, then the configured action will be taken.
ote:
N
Setpoint ranges for under voltage and overvoltage
overlap:
If both are used in an application, under
voltage pickup should always be set less than over
voltage pickup. If under voltage pickup is set higher
than overvoltage pickup and the breaker is closed, the
trip unit will see one or both conditions pickup satis-
fied, begin timing and trip.
3.7.3 Voltage unbalance
If the difference between the maximum and minimum of any
of the three line-to-line voltages is greater than the pickup
for the time delay, then the action will be taken. Action will
be taken only when at least one line-to-line voltage is greater
than 84 V.
The calculation for the voltage unbalance pickup is:
3.7.4 Current unbalance
The RMS current in each of the phases (Ia, Ib, Ic) is continu-
ously monitored. Unbalance protection will protect against
partial or full loss of one or two phases. If the difference
between the maximum and minimum of any of the three
phase currents is greater than the pickup for the time delay,
then the protection action will be taken. Action will be taken
only when at least one phase current is greater than 50% of
the long delay pickup (LDPU or Ir) setting.
The calculation for the current unbalance and phase loss
pickup is:
Max Vab Vbc Vca Min Vab Vbc Vca
Max Vab Vbc Vca
(
,
,
)
(
,
,
)
(
,
,
)
%
100
Max Ia Ib Ic
Min Ia Ib Ic
Max Ia Ib Ic
( , , ) (
( , , )
( , , )
%
100
