ABB RELION 620 Series Technical Manual page 520

Section 4
Protection functions
4.7.3.4
514
Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of the three-phase underexcitation protection function can be described
using a module diagram. All the modules in the diagram are explained in the next sections.
I_A
I_B
I3P
I_C
I1
U_A
U_B
U_C
U3P U_AB
U_BC
U_CA
U1
EXT_LOS_DET
BLOCK
BLK_TRIP
BLK_PICKUP
FR_TIMER
GUID-134FE243-96E9-4B5D-BEB2-75DB0AEE5FC5 V1 EN
Figure 245: Functional module diagram
Impedance calculation
This module calculates the apparent impedance based on the selected voltages and
currents. The Measurement mode and Phase Sel for Z Clc settings determine which
voltages and currents are to be used. If the Measurement mode is set to "1Phase-earth" or
"1Phase-phase", the Phase Sel for Z Clc setting is needed for determining which phase or
phase-phase voltages ("A or AB", "B or BC" and "C or CA") and currents should be used
for calculating the impedance.
Table 376: Voltages and currents used in impedance calculation
Measurement mode Phase Sel for Z Clc
1Phase-earth
1Phase-earth
1Phase-earth
1Phase-phase
1Phase-phase
1Phase-phase
Table continues on next page
Impedance
Impedance
reach
calculation
check
External
loss
detection
Voltages and currents
A or AB U_A, I_A
B or BC U_B, I_B
C or CA U_C, I_C
A or AB U_AB, I_A, I_B
B or BC U_BC, I_B, I_C
C or CA U_CA, I_C, I_A
1MAC504801-IB E
Timer
TRIP
t
PICKUP
620 series ANSI
Technical Manual