TD_MRN3-3_08.06_GB
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5.4.5 Parameter setting of the voltage
functions
The function of the additional voltage elements is de-
termined by means of a separately adjusted value,
that either parameterizes the related function as over-
voltage (U>) or as under voltage (U<). The adjustable
parameters are indicated by LEDs flashing in two col-
ors. When setting the voltage pick-up values U1, U2
and U3, the LEDs U1, U2 and U3 will flash in green,
at setting of the related pick-up delay times t
U1
, t
U2
and
t
U3
, the LED t> additionally flashes in red.
Pick-up values of the voltage supervision
When adjusting the pick-up values U1, U2 and U3,
the values on the display are indicated in Volt. By set-
ting the pick-up values to “EXIT”, each individual step
can be deactivated.
Tripping delay of the voltage supervision
When adjusting the tripping delay time tU1 (U1+t>),
tU2 (U2+t>) and tU3 (U3+t>), the value on the dis-
play is indicated in seconds. The tripping delay time
can be adjusted from 0.04s to 290s and the set val-
ues be stored via push-button <ENTER>.
When the tripping delay time was set to “EXIT”, it is
indefinite, i.e. there will be warning only, no tripping.
5.4.6 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,
MRN3
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.
5.4.7 Threshold of the frequency
supervision
The frequency supervision of
MRN3
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 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 f
N
.
5.4.8 Tripping delays for the frequency
elements
Tripping delays t
f1
- t
f3
of the three frequency elements
can be set independently from t
f1min
- 290 s. The mini-
mum tripping delay t
f1min
of the relay depends upon the
number 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.
