ABB RED615 Technical Manual page 473

1YHT530004D05 D
615 series
Technical Manual
U_A_AB
Level
U_B_BC
detector
U_C_CA
BLOCK
GUID-D71B1772-3503-4150-B3FE-6FFD92DE5DB7 V2 EN
Figure 249: 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
over 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
IDMT curves for overvoltage protection
Timer
Phase
selection
t
logic
t
Blocking
logic
IDMT curve saturation of the
section in this manual.
Section 4
Protection functions
OPERATE
START
section in this manual.
467