Eaton Magnum PXR - Page 60

60
Magnum PXR applications
MAGNUM PXR PRODUCT GUIDE PA013006EN September 2022 www.eaton.com
5
Residual sensing
This is the standard or default wiring configuration. It is
also the industry’s most common mode of ground fault
sensing used in 3-pole and 4-pole breaker applications.
One current sensor per pole on each phase conductor
is provided internal to the circuit breaker. When 3-pole
breakers are applied on 3-phase, 4 wire systems, an
external sensor is mounted on the switchgear neutral
bus. It is then wired to the breaker secondary contacts to
connect all sensors in the residual circuit.
The pickup (I
g
) is expressed as a multiple of the frame’s
current rating (I
n
) for circuit breakers less than 1200A.
For breakers 1200A and greater, the pickup setting is
expressed as a multiple of 1200A (the NEC maximum),
see Table 21.
Table 21. Residual sensing pickup (I
g
) values
Setting PXR 25 from 0.2 to 1.0 in steps of 0.01
Rating PXR 20 0.2 0.4 0.6 0.8 1.0
less than
1200 A
I
g
= 0.2 x (I
n
) 0.4 x (I
n
) 0.6 x (I
n
) 0.8 x (I
n
) 1.0 x (I
n
)
1200 A
or greater
I
g
= 240 480 720 960 1200
The time delay ranges from 0.05 to 1.0 seconds. Two
ground fault protection curve slopes are available: a fixed
time (flat) or I
2
t response. The slope should be chosen to
match the selective coordination requirements. The I
2
t
response provides a longer time delay for current below
0.625 x I
n
then there is a fixed time (flat) response.
ote:N For a main-tie-main system, current sensors and
ratings must be the same for the system to work
properly.
Source ground sensing
Source ground sensing is commonly found on 3-pole
breakers applied as a main breaker on single-ended radial
or on double-ended systems where a mid-point grounding
electrode is employed. The ground fault trip unit should
be configured for source ground/ zero sequence sensing
using PXPM software connected to the trip unit or through
the front display stepping to the configuration setpoints.
In the setpoints a selection of the source ground /zero
sequence sensor ratios can be made from the available
settings. A range of ratios from 1200A:1A to 10A:1A are
capable. An external current sensor is mounted with the
grounding conductor passing through the window of the
CT to measure the ground current. The current flowing in
the total ground current. The sensor is then wired to the
breaker secondary contacts C7 and C8.
The sensor used for both Source Ground and Zero
Sequence sensing methods is an iron-core CT, connected
to the secondary wiring terminals at C7 and C8. See
the Breaker Secondary Section for Magnum PXR
terminal numbering. The input at C7 and C8 is 100mA
per unit. To use a CT that has a 1A per unit secondary
you must convert the 1A level to 100mA by using the
PDGXGFSTM1A adapter module. The module contains
a 10:1 transformer, as described in Instructional Leaflet
IL012309EN. Select the ratio setting on the trip unit menu
or in PXPM assuming the 10:1 adapter module is being
used. Alternatively, a CT for example, a 1000:1 ratio could
be used as a 100:1 transformer without the converter.
Therefore, a 100mA would be equivalent to 100A on the
primary of the 1000:1 transformer.
Zero sequence sensing
Zero sequence ground fault protection can be applied
on any main, feeder, and other breakers with a ground
fault PXR trip unit. The ground fault trip unit should be
configured for zero sequence/source ground sensing using
PXPM software connected to the trip unit or through the
front display stepping to the configuration setpoints. In the
setpoints a selection of the Zero sequence sensor ratio
can be made from the available settings. A range of ratios
from 1200A:1A to 10A:1A are capable. The zero sequence
sensors are wired to breaker secondary contacts C7 and
C8. The secondary current rating of the sensor must be 1
ampere. See the Source Ground section for CT ratio usage
and programming.
Table 22. Source ground/ZS sensing pickup (I
g
) values
Physical CT
combination
Setting 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 + 10:1 1200:1 I
g
= 240 480 720 960 1200
1000:1 + 10:1 1000:1 I
g
= 200 400 600 800 1000
800:1 + 10:1 800:1 I
g
= 160 320 480 640 800
400:1 + 10:1 400:1 I
g
= 80 160 240 320 400
200:1 + 10:1 200:1 I
g
= 40 80 120 160 200
100:1 + 10:1 100:1 I
g
= 20 40 60 80 100
1000:1 100:1 I
g
= 20 40 60 80 100
50:1 + 10:1 50:1 I
g
= 10 20 30 40 50
500:1 50:1 I
g
= 10 20 30 40 50
25:1 + 10:1 25:1 I
g
= 5 10 15 20 25
250:1 25:1 I
g
= 5 10 15 20 25
10:1 + 10:1 10:1 I
g
= 2 4 6 8 10
100:1 10:1 I
g
= 2 4 6 8 10