5 Mounting
Maschinenfabrik Reinhausen GmbH 2020
51
4983703/01 EN
VACUTAP
®
VV-Ex
5.3.4 Performing DC resistance measurement on transformer
The measured DC current is normally restricted to 10% of the rated current
of the measured transformer winding in order to prevent the winding from
overheating.
Perform the DC resistance measurement in various on-load tap-changer op-
erating positions. You need to distinguish here whether the measured cur-
rent is interrupted when changing operating position or not.
Status of oil compart-
ment
Without interruption in
measured current
With interruption (mea-
sured current = 0 A be-
fore change of operating
position)
Oil compartment empty
Maximum 10 A DC
Maximum 50 A DC
Oil compartment filled with
insulating fluid
Maximum 50 A DC
Maximum 50 A DC
Table 11: Maximum permitted measured currents when performing DC resistance measurement
on transformer
5.3.5 Drying on-load tap-changer in autoclave
NOTICE
Damage to the on-load tap-changer!
Moisture in the oil compartment reduces the dielectric strength of the insu-
lating fluid and thus leads to damage to the on-load tap-changer.
► Within 10 hours of drying, seal off oil compartment with on-load tap-
changer head cover.
Dry on-load tap-changer in accordance with the following instructions to en-
sure the dielectric values assured by MR for the on-load tap-changer.
If drying in an autoclave, the following methods are possible:
▪ Vacuum drying
▪ Vapor-phase drying
As an alternative to drying the on-load tap-changer in an autoclave, it can
also be dried in the transformer tank.
5.3.5.1 Vacuum-drying in the autoclave
Before starting vacuum-drying in the autoclave, you must remove the on-
load tap-changer head cover and on-load tap-changer accessories:
1.
NOTICE!
Remove the on-load tap-changer head cover (24 screws M10/
wrench size 17 with safety elements) and store it outside the autoclave. If
this is not done, the on-load tap-changer head cover may be damaged.
2.
NOTICE!
Remove on-load tap-changer accessories and store outside au-
toclave: motor-drive unit, drive shaft, protective relay, bevel gear, temper-
ature sensor. If this is not done, the on-load tap-changer accessories may
be damaged.