Transformer Testing
AVTMTO3XX Rev 3 Sept 2013
37
Because the instrument can be left on while changing from tap to tap, it
is possible to take measurements without discharging. The MTO will re-
balance after every tap change. If the current drops more than 10% for
the selected transition time sensitivity, then the MTO will indicate there
was a transition.
The transition times are set to 5ms, 20ms, 80ms and Off.
If a transition is detected over 5 msec and under 200 msecs, the unit will
flag a transition, but the current will continue flowing. The same thing
goes for 20 and 80 millisecond settings. If a transition is detected, the
unit will define the transition test time and the pass or fail test result.
If the current interruption is longer than about 200 ms, the MTO will
stop the test and discharge the transformer automatically.
Demagnetizing a Transformer
The MTO demagnetizes the transformer by automatically magnetizing the core
of the transformer in the positive and negative direction with multiple cycles of
reduced current. The demagnetization function is equivalent to generating test
currents for multiple resistance tests. During the demagnetizations cycle, the unit
will display the number of cycles left in the process.
1. Demagnetization only needs to be accomplished once after all testing is
complete.
2. Test leads should be attached to one terminal pair on high side (Primary)
windings for effective demagnetization. eg. H1-H2 is the standard
terminal connection that the MTO will drive current through.
3. Only one terminal pair (winding) needs to be demagnetized on a three-
phase transformer.
4. Press the DEMAG Button
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