19
MVTU 18 – neutral displacement
Time delay t
1
is checked as for MVTU 13
Time delay t
2
is checked by connecting the timer as shown in Figure 4 and repeating
the tests as for time delay t
1
.
Figure 4 Test circuit for MVTU 18 relay
4.5.6 Final setting checks
Adjust the voltage setting to its functional setting and measure the pick-up and drop-
off values as already mentioned. Check that they are within the stated tolerance.
With the final voltage setting and the functional timer setting selected, measure the
operating times when a voltage ≥1.1x the setting voltage is applied (≤0.9x for MVTU
11). Check that this is within the stated tolerance.
4.5.7 Trip indicator and contact check
Check that the trip indicator and reset facility operate. Also check that the contacts
operate by carrying out continuity checks.
4.5.8 Final checks
Operate the relay with the trip and alarm links restored to ensure that the trip and
alarm circuits are energised according to the relevant schematic diagram.
Remove all test leads, test switches, temporary shorting leads etc.
Replace any links that have been removed to facilitate testing.
If a test plug (MMLB) and test block (MMLG) have been used, remove the test plug.
CAUTION:
Replace the test block cover to put the protection in service.
27
28
1
3
5
V
Start
timer T1
SW1
Stop timer
T1
2
4
6
Start
timer
T2
7
9
1
Stop timer
T2
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