Page 54 - Energize October 2021
P. 54
TECHNICAL
Figure 10
Figure 8 Figure 11
Figure 12
Conclusions
Routine electrical and dielectric testing on the YNd1 25 MVA
transformer did not provide clear indication of mechanical damage in
the seventeen-position resistive-type OLTC.
True DRM allows for identification of faulty components affecting
the resistive characteristic of the transition resistors in the OLTC.
Megger suggests that a make-before-break test is included as part
of the static winding resistance test.
The DRM procedure does not add significant testing time, but it
shows great value in identifying defects in transition resistors or their
connections to the transition arcing contact.
The normal WRM test did not indicate any problem, nor did any
of the other tests performed, except for the DRM test. DRM testing is
Figure 9 useful for power transformer OLTC assessment. n
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