Deif CGC 400 - Page 94

Phase-neutral Phase-phase
U
L3-L1
U
L1-N
U
L1-L2
U
L2-L3
U
L
2
-
N
U
L
3
-
N
U
L3-L1
U
L1-N
U
L1-L2
U
L2-L3
U
L
2
-
N
U
L
3
-
N
As indicated in the vector diagram, there is a difference in voltage values at an error situation for the phase-
neutral voltage and the phase-phase voltage.
The table shows the actual measurements at a 10% undervoltage situation in a 400/230 volt system.
Phase-neutral Phase-phase
Nominal voltage 400/230 400/230
Voltage, 10% error 380/207 360/185
The alarm will occur at two different voltage levels, even though the alarm setpoint is 10% in both cases.
Example
The below 400V AC system shows that the phase-neutral voltage must change 20%, when the phase-phase
voltage changes 40 volts (10%).
Example:
U
NOM
= 400/230V AC
Error situation:
U
L1L2
= 360V AC
U
L3L1
= 360V AC
U
L1-N
= 185V AC
ΔU
PH-N
= 20%
U
L3-L1
U
L1-N
U
L1-L2
U
L2-L3
U
L
2
-
N
U
L
3
-
N
20%
Both the generator protections and the busbar/mains protections use phase-phase voltage.
CGC 400 DRH 4189340786 UK Protections
DEIF A/S Page 94 of 96