ABB RELION 620 Series Technical Manual page 305

1MAC504801-IB E
620 series ANSI
Technical Manual
If the input frequency (f
m
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 trip 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
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.
The beginning of the cooling process deactivates the TRIP output and activates the
COOL_ACTIVE output. COOL_ACTIVE is kept active during the cooling process. If a
new overexcitation start ceases cooling, COOL_ACTIVE is deactivated during that start
time. BLK_RESTART is kept active until the set total cooling time has elapsed. It means
that even during the new overexcitation start ceases cooling, BLK_RESTART is kept
active. Due to the updated cooling time, the BLK_RESTART activation time is prolonged
with these new starts during cooling. A new overexcitation start during cooling does not
immediately reactivate TRIP, but PICKUP is first activated and a new TRIP activation
depends on the already run cooling time. If, for example, 60 percent of the set cooling time
has run before a new start, 40 percent of the operating time is needed to reactivate TRIP.
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.
) is less than 20 percent of the nominal frequency (f
Timer characteristics
Section 4
Protection functions
n
chapter.
), the
299