ABB RELION 611 Series Technical Manual page 259

1MRS757454 D
611 series
Technical Manual
U_A_AB
Level
U_B_BC
detector
U_C_CA
BLOCK
GUID-D71B1772-3503-4150-B3FE-6FFD92DE5DB7 V2 EN
Figure 121: Functional module diagram
Level detector
The fundamental frequency component of the measured three-phase voltages are
compared phase-wise to the set value of the Start value setting. If the measured value
is higher than the set value of the Start value setting, the level detector enables the
phase selection logic module. The Relative hysteresis setting can be used for
preventing unnecessary oscillations if the input signal slightly differs from the Start
value setting. After leaving the hysteresis area, the start condition has to be fulfilled
again and it is not sufficient for the signal to only return to the hysteresis area.
The Voltage selection setting is used for selecting phase-to-earth or phase-to-phase
voltages for protection.
For the voltage IDMT operation mode, the used IDMT curve equations contain
discontinuity characteristics. The Curve Sat relative setting is used for preventing
undesired operation.
For a more detailed description of the IDMT curves and the use of the
Curve Sat Relative setting, see the
voltage protection
Phase selection logic
If the fault criteria are fulfilled in the level detector, the phase selection logic detects
the phase or phases in which the fault level is detected. If the number of faulty phases
match with the set Num of start phases, the phase selection logic activates the Timer.
Timer
Once activated, the Timer activates the START output. Depending on the value of the
set Operating curve type, the time characteristics are selected according to DT or
IDMT.
For a detailed description of the voltage IDMT curves, see the
curves for overvoltage protection
Timer
Phase
selection
t
logic
t
Blocking
logic
IDMT curve saturation of the over
section in this manual.
section in this manual.
Section 4
Protection functions
OPERATE
START
IDMT
253