SEG Electronics GmbH
Manual MRG3
68
DOK-TD-MRG3, Rev. D
6.5.4 Checking the operating and resetting values of the relay
Impress a current which is less than the relay set values in phase 1 of the relay and gradually in-
crease the cur-rent until the relay starts, i.e. at the moment when the LED I> and L1 light up or the
alarm output relay I> is activated. Read the operating current indicated by the ammeter. The devia-
tion must not exceed 3% of the set operating value of the MRG3-I or 1% In.
Furthermore, gradually decrease the test current until the relay resets, i.e. the alarm output relay I>
is disengaged. Check that the resetting current is smaller than 0.97 times the operating current.
Repeat the test on phase 2, phase 3 and earth current input circuits in the same manner.(Accuracy
of earth current measuring ±3% of measuring value or
0.1% of In
6.5.5 Checking of the tripping delay
To check the tripping delay, a timer must be connected to the trip contact of the output relay. The
timer should be started simultaneously with the current injection 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 instantaneously. 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 EN60255-3
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 read 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 maintained stable
(deviation <1% since otherwise the test results might be distorted.
6.5.6 Checking the high set element of the relay
Set a current above the set operating value of short circuit element I>>. Impress the current instan-
taneously and check that the alarm output relay I>> is energized. When doing so, the over current
step I> should be blocked before setting (it to EXIT). Check the tripping time of the high set ele-
ment according chapter 6.5.5. Check the accuracy of the operating current setting by gradually in-
creasing the impressed 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 current 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 considered (see technical data, chapter 7.3).
