TD_MRI1_06.05_GB
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6.4.5
Checking the relay operating time
To check the relay operating time, a timer must be
connected to the trip output relay contact. The timer
should be started simultaneously with the current injec-
tion in the current input circuit and stopped by the trip
relay contact. Set the current to a value corresponding
to twice the operating value and inject the current in-
stantaneously. The operating time measured by the
timer should have a deviation of less than 3% of the
set value or
±
10 ms (DEFT). Accuracy for inverse time
characteristics refer to IEC 255-3.
Repeat the test on the other phases or with the inverse
time characteristics in the similar manner.
In case of inverse time characteristics the injected cur-
rent should be selected according to the characteristic
curve, e.g. two times I
S
. The tripping time may be red
from the characteristic curve diagram or calculated
with the equations given under "technical data".
Please observe that during the secondary injection test
the test current must be very stable, not deviating more
than 1%. Otherwise the test results may be wrong.
6.4.6
Checking the high set element
of the relay
Set a current above the set operating value of I>>. In-
ject the current instantaneously and check that the
alarm output relay I>> operates. Check the tripping
time of the high set element according chapter 6.4.5.
Check the accuracy of the operating current setting by
gradually increasing the injected current until the I>>
element picks up. Read the current value form the am-
meter and compare with the desired setting.
Repeat the entire test on other phases and earth cur-
rent input circuits in the same manner.
Note !
Where test currents >4 x I
N
are used, the thermal with-
stand capability of the current paths has to be consid-
ered (see technical data, chapter 7.1).