Rockwell Automation 825 Smart Motor Manager User Manual - Manual (Page 64)

3-31 Functions
Publication 825-UM001B-EN-P January 2001
Schematic Representation of Various Network Configurations and Earth (Ground) Fault
Locations
The earth (ground) fault current measured by the Smart Motor Manager with the aid of a core
balance current transformer is dependent on the power supply network configuration and on
the location of the earth fault. The following diagrams indicate the relationships in the various
applications.
The symbols used have the following meanings:
C
N
Earth capacitance of phase conductor on power supply system side
C
M
Earth capacitance of motor including supply conductors between current transformer
and motor
L Compensating coil
R High earthing resistance
T Transformer
,
E
Earth (ground) fault current
Figure 3.15 Isolated Network: Earth Fault on the Network Side
The basic unit measures the earth current component through C
M
.
Figure 3.16 Network Earthed through a High Impedance: Earth Fault on the
Network Side
The basic unit measures the earth current component through C
M
. Compensated network: Through the fault a small current
flows, given by the vector sum of the earth currents.
3 AC
U3
U1 U2
T
1
2
3
K1
825-M
M1
CN I E CM
3 AC
U3
U1 U2
T 1
2
3
K1
825-M
M1
CN I E CM R L