Section 4
1MAC050144-MB C
Protection functions
224
615 series ANSI
Technical Manual
Figure 106:
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
Pickup value
setting. If the measured value is
higher than the set value of the
Pickup 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
Pickup value
setting.
After leaving the hysteresis area, the pickup 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-ground 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.
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 pickup phases
, the phase selection logic activates the timer.
Timer
Once activated, the timer activates the
PICKUP
output. Depending on the value of the set
Operating curve type
, the time characteristics are selected according to DT or IDMT.
When the operation timer has reached the value set by
Trip delay time
in the DT mode or
the maximum value defined by the IDMT, the
TRIP
output is activated.
For a more detailed description of the IDMT curves and the use of the
Curve Sat Relative
setting, see the General function block features section
in this manual.
For a detailed description of the voltage IDMT curves, see the General
function block features section in this manual.
V_A_AB
V_B_BC
V_C_CA
Level
detector
Phase
selection
logic
Timer
t
t
Block
Block
logic
Trip
Pickup
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