TB MRU3-2 12.00 E
27
The test can basically be carried out with any phase.
The result of the measurement differs only in the indi-
cating values for the phase voltages L1-L3.
Measuring
value
indication
L1
0
L2, L3
U
N
U1
≈
2/3
×
U
N
U2
≈
1/3
×
U
N
U0
≈
1/3
×
U
N
Table 6.3: Indication at phase failure
Earthfault
For this test all conductors L1-L3 have to be correctly
connected. The star point N from the mains is not con-
nected. Instead the star point of the
MRU3-2
is con-
nected with phase L1. This type of connection simu-
lates an earthfault of phase L1.
Measuring
value
Indication
L1
0
L2, L3
3
×
U
N
U1
≈
U
N
U2
≈
0
U0
≈
U
N
Table 6.4: Indication at earthfault
6.4.4
Checking the operating and reset-
ting values of the over/under-
voltage functions
Apply three voltages with the rated value and gradu-
ally increase (decrease) the voltages until the relay
starts, i.e. at the moment when the LED U> (or U<)
lights up or the voltage alarm output relay (contact ter-
minals D4/E4) is activated. Read the operating volt-
age indicated by the voltmeter. The deviation must not
exceed 1% of the set operating value.
Furthermore, gradually decrease (increase) the volt-
ages until the relay resets, i.e. the voltage alarm output
relay is disengaged. Check that the dropout to pickup
ratio is greater than 0.97 (for overvoltage function) or
smaller than 1.03 (for undervoltage).
6.4.5
Checking the relay operating time
of the over/undervoltage functions
To check the relay's operating time, a timer must be
connected to the trip outpnut relay contact (Contact
terminals D1/E1).
It must be ensured that the respective output relay is
assigned to the function to be tested. (refer to chapter
5.9.1).
The timer should be started simultaneously with the
voltage change from sound condition to a faulty condi-
tion and stopped by the trip relay contact. The operat-
ing time measured by timer should have a deviation
about 3% of the set value or < 20 ms.
6.4.6
Checking the external blocking
and reset functions
The external blocking input blocks the selected voltage
functions.
Care must be taken that these terminals are also as-
signed the blocking function (refer to chapter 5.9.1).
The external blocking input inhibits undervoltage func-
tions. To test the blocking function apply auxiliary sup-
ply voltage to the external blocking input of the relay
(terminals E8/D8). Inject a test voltage which could
cause tripping for the functions above mentioned. Ob-
serve that there is no trip and alarm.
Remove the auxiliary supply voltage from the blocking
input. Apply test voltages to trip the relay (message
„TRIP“ on the display). Return the test voltages to the
sound condition and apply auxiliary supply voltage to
the external reset input of the relay (terminals C8/D8).
The display and LED indications should be reset im-
mediately.
