ABB RELION REX640 Technical Manual page 888

Protection functions
The excitation level (M) can be calculated:
M
=
M
E
f
m
U
n
f
n
If the input frequency (f
calculation of the excitation level is disabled and forced to zero value. This means
that the function is blocked from starting and operating during a low-frequency
condition.
The calculated excitation level (U/f ratio or volts/hertz) VOLTPERHZ is available in
the Monitored data view.
Level detector
Level detector compares the calculated excitation level to the
the excitation level exceeds the set limit, the module sends an enabling signal to
start Timer.
Timer
Once activated, Timer activates the START 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
DT mode or the value defined by the inverse time curve, the OPERATE output is
activated.
In a drop-off situation, that is, when the excitation level drops below
before the function operates, the reset timer is activated and the START output
resets after the time delay of
the IDMT curves, the reset operation is as described in
characteristics
For the IDMT curves, it is possible to define the maximum and minimum operating
times via the
Maximum operate time setting is used to prevent infinite start situations at low
degrees of overexcitation. The
operate times.
The activation of the OPERATE output activates the BLK_RESTART output.
For the DT characteristics, the deactivation of the OPERATE output activates the
cooling timer. The timer is set to the value entered in 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 OPERATE
output is activated immediately. For IDMT, the deactivation of BLK_RESTART and
COOL_ACTIVE depends on the curve type selected.
888
E
f
m
U Volt Max continuous
n
⋅
f
100
n
excitation level (U/f ratio or volts/hertz) in pu
internal induced voltage (emf)
measured frequency
nominal phase-to-phase voltage
nominal frequency
) is less than 20 percent of the nominal frequency (f
m
.
Minimum operate time and Maximum operate time settings. The
Reset delay time for the DT characteristics. For
Time multiplier setting is used for scaling the IDMT
1MRS759142 F
(Equation 247)
Start value setting. If
Operate delay time in the
Start value
Chapter 4.5.7.6 Timer
Cooling time setting. The
Technical Manual
), the
n
REX640