Manual MRN3 GB
Woodward
TD_MRN3_09.08_GB_Rev.New
27
5.4 Protection
parameters
5.4.1 Parameter setting of over- and under voltage supervision
The setting procedure is guided by two colored LEDs. During setting of the voltage thresholds the
LEDs U<, U<<, U> and U>> are lit green. During setting of the trip delays t
U>
, t
U>>
, t
U<
and t
U<<
the
according LEDs light up red.
Thresholds of the voltage supervision
During setting of the threshold U>, U>>, U< and U<< the displays shows the voltages directly in
volt. The thresholds can be changed by the <+> <-> push buttons and stored with <ENTER>.
The under voltage supervision (U< and U<<) as well as the overvoltage supervision (U> and U>>)
can be de-activated by setting the threshold to "EXIT".
Tripping delay of voltage supervision
During setting of the tripping delays t
U<
, t
U<<
, t
U
> and t
U
>> the display shows the value directly in
seconds. The tripping delay is changed via the push button <+> and <-> in the range of 0,04 s to
50 s and can be stored with the push button <ENTER>.
When setting the tripping delay to "EXIT" the value is infinite meaning only warning, no tripping.
5.4.2 Number of measuring repetitions (T) for frequency functions
In order to avoid false tripping of the unit at short voltage drops of the system voltage or interfe-
rence voltages, MRN3 works with an adjustable measuring repetition. When the instantaneous fre-
quency measuring value exceeds (at over frequency) or falls below (at under frequency) the set
reference value, the counter is incremented, otherwise the counter is decremented down to the
minimum value of 0. Only when the counter exceeds the value adjusted at T, alarm is given and af-
ter 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.
5.4.3 Threshold of frequency supervision
The frequency supervision of MRN3 has three frequency 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 under 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 f1 - f3 the display shows the values in Hz. A value of for in-
stance 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 frequency.
