5 Mounting
Maschinenfabrik Reinhausen GmbH 2020
96
7545652/00 EN
VACUTAP
®
VR-Ex
If drying in the transformer tank, the following methods are possible:
▪ Vacuum-drying
▪ Vapor-phase drying
As an alternative to drying the on-load tap-changer in the transformer tank, it
can also be dried in an autoclave.
5.3.6.1 Vacuum-drying in the transformer tank
The on-load tap-changer head cover remains closed during the entire drying
process.
1. Establish a connecting lead between either connections E2 and Q or con-
nections E2 and R on the on-load tap-changer head.
2. Seal off unused pipe connections with a suitable blank cover.
Figure 95: Connecting lead
Vacuum-drying in the transformer tank
1. Heat up the on-load tap-changer in air at atmospheric pressure with a
temperature increase of approximately 10 °C/h to a final temperature of
maximum 110 °C.
2. Pre-dry the on-load tap-changer in circulating air at a maximum tempera-
ture of 110 °C for a period of at least 20 hours.
3. Vacuum-dry on-load tap-changer at between 105 °C and maximum
125 °C for at least 50 hours.
4. Residual pressure of no more than 10
-3
bar.
If you wish to perform another transformer ratio test after drying, proceed as
described in the section "Performing transformer ratio test following dry-
ing" [
