Melitta LOOK - Page 16

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Figure 2 Test circuit for the 220/250V and the 380/440V versions of MVTU 11 and
MVTU 12
Figure 3 Test circuit for 380/440V version of MVTU 11 and MVTU 12 when no
step-up transformer is available
MVTU 11 undervoltage relay
See Figure 1 for the test circuits for the 57/70V and 100/120V versions and Figure
2 for the 220/250V and the 380/440V versions.
If the 380/440V version is being commissioned a step-up transformer is needed to
allow the calibration of the settings to be checked.
The ac input voltage should be increased to a value above the setting value and the
trip indicator reset. Slowly decrease the input voltage until the relay picks up (when
the trip indicator operates). Record the pick-up value.
Slowly increase the voltage, checking to see when the trip indicator can be reset.
This is the drop-off value and should be recorded.
Alternatively, the pick-up and drop-off values can be determined using an ohmmeter
connected across the contacts.
27
28
1
3
5
V
Start
timer
SW1
Stop
timer
REXT
2
Step-up
Transformer
27
28
1
3
5
V
Start
timer
SW1
Stop
timer
A