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.
For a detailed description of the voltage IDMT curves, see the
curves for under voltage protection
section in this manual.
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.
When the user-programmable IDMT curve is selected, the trip time characteristics are
defined by the parameters
Curve parameter A
,
Curve parameter B
,
Curve parameter C
,
Curve parameter D
and
Curve parameter E
.
If a drop-off situation occurs, that is, a fault suddenly disappears before the trip delay is
exceeded, the reset state is activated. The behavior in the drop-off situation depends on the
selected trip time characteristics. If the DT characteristics are selected, the reset timer runs
until the set
Reset delay time
value is exceeded. If the drop-off situation exceeds the set
Reset delay time
, the Timer is reset and the
PICKUP
output is deactivated.
When the IDMT trip time curve is selected, the functionality of the Timer in the drop-off
state depends on the combination of the
Type of reset curve
and
Reset delay time
settings.
Section 4
1MAC059074-MB A
Protection functions
620
615 series ANSI
Technical Manual
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