If the input frequency (f
m
) is less than 20 percent of the nominal frequency (f
n
), the
calculation of the excitation level is disabled and forced to zero value. This means that the
function is blocked from picking up and tripping during a low-frequency condition.
The calculated excitation level (V/f ratio or volts/hertz) VOLTPERHZ is available in the
Monitored data view.
Level detector
Level detector compares the calculated excitation level to the
Pickup value
setting. If the
excitation level exceeds the set limit, the module sends an enabling signal to start Timer.
Timer
Once activated, Timer activates the
PICKUP
output. Depending on the value of the
Operating curve type
setting, the time characteristics are according to DT or IDMT. When
the operation timer has reached the value set by
Trip delay time
in the DT mode or the
value defined by the inverse time curve, the
TRIP
output is activated.
In a drop-off situation, that is, when the excitation level drops below
Pickup value
before
the function trips, the reset timer is activated and the
PICKUP
output resets after the time
delay of
Reset delay time
for the DT characteristics. For the IDMT curves, the reset
operation is as described in the
Timer characteristics
chapter.
For the IDMT curves, it is possible to define the maximum and minimum trip times via the
Minimum trip time
and
Maximum trip time
settings. The
Maximum trip time
setting is used
to prevent infinite pickup situations at low degrees of overexcitation. The
Time multiplier
setting is used for scaling the IDMT trip times.
The activation of the
TRIP
output activates the
BLK_RESTART
output.
For the DT characteristics, the deactivation of the
TRIP
output activates the cooling
timer. The timer is set to the value entered in the
Cooling time
setting. The
BLK_RESTART
and
COOL_ACTIVE
outputs are kept active until the cooling timer is
reset. If the excitation increases above the set value during this period, the
PICKUP
output
is activated immediately. For IDMT, the deactivation of
BLK_RESTART
and
COOL_ACTIVE
depends on the curve type selected.
The
T_ENARESTART
output indicates in seconds the duration for which the
BLK_RESTART
output still remains active. The value is available in the Monitored data
view.
Timer calculates the pickup duration value PICKUP_DUR, which indicates the
percentage ratio of the pickup situation and the set trip time. The value is available in the
Monitored data view.
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
645
Technical Manual
Summary of Contents for Relion 615 series
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