37
1ZSE 5492-118 en, Rev. 4
5 Final assembly
5.5.1 Transformer ratio measurement after drying
If transformer ratio measurement is to be done after drying this is a suitable stage to carry it
out.
CAUTION
To avoid seizing, do not operate the on-load tap-changer until it is lled with oil.
Carry out this measurement after the drive system is mounted.
Operate the on-load tap-changer by means of the motor-drive mechanism.
CAUTION
The on-load tap-changer should be operated through the whole operating range, both in
lower and raise direction, when carrying out ratio measurement.
The end positions must not be overrun during ratio measurement. When operating the on-
load tap-changer without drive system, check the designation of the end positions on the
single-phase diagram and watch the position indicator in the bevel gear in order to avoid
overrunning of the end position.
Watch the voltmeter during the on-load tap-changer operations. No fast voltage drops may
occur during operation. If such drops occur, the on-load tap-changer is not correctly con-
nected to the winding.
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