Allen-Bradley 1407-CGCM, User Manual, Page: 56 / 252

Rockwell Automation Publication 1407-UM001H-EN-P - November 2014
#HAPTER CGCM Unit Operation
,OSSOF3ENSING&,
For three-wire and four-wire sensing, Loss of Sensing detection is based on the
logical combination of several conditions. They include these conditions:
1. The average positive sequence voltage is greater than 8.8% of the AVR
setpoint.
2. The negative sequence voltage is greater than 25% of the positive sequence
voltage.
3. The negative sequence current is less than 17.7% of the positive sequence
current.
4. The positive sequence current is less than 1% of rated current for
0.1 seconds.
5. The generator positive sequence voltage is less than 8.8% of the AVR
setpoint.
6. The positive sequence current is less than 200% of the rated current for
0.1 seconds.
The three phase loss of sensing is expressed by this logical formula:
Loss of Sensing = ((1 and 2) and (3 or 4)) or (5 and 6)
For single-phase sensing, Loss of Sensing is detected when the following
conditions exist in the proper logical combination.
1. The average generator terminal line-to-line voltage is less than 70% of the
AVR setpoint.
2. The positive sequence current is less than 200% of the rated current.
3. The negative sequence current is less than or equal to 17.7% of the positive
sequence current.
4. The positive sequence current is less than 1% of rated current for
0.1 seconds.
The single phase loss of sensing is expressed by this logical formula:
Loss of Sensing = ((1 and 2) and (3 or 4))
The time delay for this function is fixed at 0.1 seconds during normal operation
and increased to 1.0 seconds during soft start operation. Loss of Sensing is
disabled when the excitation current is less than the Loss of Excitation setpoint. If
this fault occurs, tag
LossSensingFlt = 1 in the Scheduled Read table.