TB MRF3 04.01 E
25
6.4.3
Checking the input circuits and
measuring values
First the measuring voltage as high as the nominal
voltage is to be connected to terminals A3 and A4.
Then the actual measuring values of the frequency can
be read by pressing push button <SELECT/RESET>.
The measured frequency is indicated on the display by
the simultaneous illummination of LED f as follows:
5001; corresponds to 50.01 Hz.
The rate of change of frequency is indicated on the
display when LED df (indication in Hz/s) lights up. Ex-
ample 3.1 corresponds to 3.1 Hz/s.
6.4.4
Checking of operating- and resetting
values of the over-/underfrequency
functions
Note!
During frequency test each of the four frequency ele-
ments should be checked. To guarantee a trouble-free
test run the other frequency elements of the unit have
therefore to be blocked at the beginning by adjusting
the corresponding frequency operating values f1 - f4
to "EXIT".
To check the operating- and reset values the test fre-
quency must be increased or decreased until the relay
picks up. This is signalized when LEDs f
1
- f
4
light up.
When comparing the values indicated on the display
with those of the frequency meter, the deviation must
not exceed more than 0.01 Hz.
The reset values are detected by increasing or de-
creasing the test frequency slowly till the output relay
releases.
The reset value for overfrequency must be smaller than
the setting value of fx+R, for underfrequency it must be
larger than the setting value of fx+R.
6.4.5
Checking of operating- and resetting
values of the df/dt elements
Note!
During testing the df/dt function the two frequency
elements should be checked individually. Therefore the
other frequency functions must be blocked by adjusting
the pickup values to "EXIT".
Frequency threshold fe and the df/dt function can,
however, only be tested with a function generator
which can generate a definite frequency gradient.
6.4.6
Checking the tripping delays
For checking the tripping delays t
f
a voltage source is
needed which changes the frequency in a defined
quantity at a certain time and at the same time gener-
ates an output signal.
While checking the tripping delay a timer can be
connected with the contact of the tripping relay. The
timer is simultaneously started with the change of the
frequency and stopped when the relay trips. Hereby
the test frequencies have to be selected so that the re-
lay detects a safe under- or overfrequency. The trip-
ping time measured with the aid of the timer should not
deviate more than 3%, or more than 20 ms (at short
tripping delay), from the set tripping delay.
It is to be observed that the measured time till tripping
is longer by the number of the measuring periods (T) to
be evaluated than the set tripping delay.
6.4.7
Checking the reclaim time of the
frequency stages
The reclaim time are checked the same way as the trip
delays. The difference in the tests is that the set fre-
quency must lie above the excitation point and is rest
below the excitation point after tripping has occurred
in order to be able to determine the switch-off time.
6.4.8
Checking the external blocking- and
reset functions
The external blocking input blocks the underfrequency
and df/dt functions of the
MRF3
which are selected in
the assignment mode (please refer to tab. 5.2 , page
16)
At the beginning of the test the auxiliary voltage is
connected to terminals D8/E8 of the unit. Then a test
frequency has to be set which normally leads to trip-
ping of one of the frequency functions. Neither an
alarm nor tripping must take place.
After this the auxiliary voltage has to be removed from
the blocking input. Changing the frequency again by
the same amount, the relay trips and the signal "TRIP"
appears on the display. After this the test frequency
must be set again to a value which does not lead to
tripping. By applying auxiliary voltage to the reset in-
put (C8/D8), the LED indication extinguishes and the
display resets.
Содержание MRF3
Страница 1: ...MRF3 Frequency Relay...
