Deif GPC-3 - Page 95

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 % under-voltage 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 set point is 10 % in both cases.
Example
The below 400 V AC system shows that the phase-neutral voltage must change 20 %, when the phase-phase
voltage changes 40 volts (10 %).
Example:
U
NOM
= 400/230 V AC
Error situation:
U
L1L2
= 360 V AC
U
L3L1
= 360 V AC
U
L1-N
= 185 V 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%
Phase-neutral or phase-phase: both the generator protections and the busbar/mains protec-
tions use the selected voltage.
The protection calculates the over-current set point as a function of the measured voltage on the generator
voltage terminals.
GPC-3 DRH 4189340587 UK
Protections
DEIF A/S Page 95 of 122