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TB XRW1-4 04.01 E
6.2.2
Setting of nominal frequency
First the nominal frequency (50 or 60 Hz) has to be
correctly set before unit
XRW1-4
is put into operation.
All frequency functions are determined by setting the
nominal frequency, i.e. whether the set frequency
thresholds are evaluated as over- or underfrequency
(see also chapter 6.2.4). Also the cycle duration
(20 ms at 50 Hz and 16.67 ms at 60 Hz) derives
from this setting which determines the minimum tripping
delay for frequency elements f
1
- f
3
with an adjustable
multiplier (see also chapter 6.2.5).
During setting of the nominal frequency a value in Hz is
shown on the display.
6.2.3
Number of measuring repetitions (T)
for frequency functions
In order to avoid false tripping of the unit at short volt-
age drops of the system voltage or interference volt-
ages,
XRW1-4
works with an adjustable measuring
repetition. When the instantaneous frequency measur-
ing value exceeds (at overfrequency) or falls below (at
underfrequency) the set reference value, the counter is
incremented, otherwise the counter is decremented
down to the minimum value of 0. Only when the coun-
ter exceeds the value adjusted at T, alarm is given and
after the tripping delay of the frequency element has
elapsed the tripping command is given.
The setting range for T is between 2 - 99.
Recommendation for setting:
For short tripping times, e.g. for machine protection or
for mains decoupling T should be set in the range from
2 - 5.
At precision measurements, e.g. exact measurement of
the system frequency a setting of T in the range from
5 - 10 is recommended.
6.2.4
Threshold of frequency supervision
The frequency supervision of
XRW1-4
has three fre-
quency elements independent from each other. Acc. to
setting the pickup value above or below the nominal
frequency, these elements can be used for over- or un-
der frequency supervision.
Dependent on the preset nominal frequency f
N
the
pickup values from 30 Hz up to 70 Hz at f
N
= 50 Hz
and from 40 Hz to 80 Hz at f
N
= 60 Hz can be set.
During setting of the pickup values f
1
- f
3
the display
shows the values in 1/100 Hz. A value of for instance
49,8 Hz is indicated with "4980".
The function of the individual frequency elements can
be deactivated by setting the pickup values to "EXIT".
The setting value “EXIT“ corresponds to the rated fre-
quency.
6.2.5
Tripping delays for the frequency
elements
Tripping delays t
f1
- t
f3
of the four frequency elements
can be set independently from t
f1min
- 50 s. The minimum
tripping delay t
f1min
of the relay depends upon the num-
ber of set measuring repetitions T (periods) and
amounts to:
T
t
f,min
2....49
(T+1)·20 ms
50....69
(T - 49)·50 ms + 1 s
70....99
(T - 69)·100 ms + 2 s
When setting the tripping delay to "EXIT" by pressing
push button <+> up to the maximum setting value, the
corresponding tripping relay is blocked. Pickup of the
frequency element is however displayed on the front
plate by the corresponding LED, an assigned alarm re-
lay is also activated. This setting applies to 50 Hz and
60 Hz.
