ABB RELION REF615R, Technical Manual

Page: 255 / 664

The excitation level (M) can be calculated:
M
E
f
V
f
Volt Max continuous
m
n
n
=
⋅
100
GUID-2712EB3B-0126-44B6-AABC-AA4BD2569FFB V1 EN
(Equation 3)
M excitation level (V/f ratio or volts/hertz) in pu
E
internal induced voltage (emf)
f
m
measured frequency
V
n
nominal phase-to-phase voltage
f
n
nominal frequency
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.
1MRS240050-IB C
Section 4
Protection functions
REF615R 249
Technical Manual