ABB Power Grids Ltd.
GKSL 680205.021 RE
Rev. 2, 26.09.2019
11
10.2
Capacitance C
1
and tg
δ
1
measurements
First de-energize the transformer, then take the test tap cover off and connect the measuring equipment to
it using the test adapter, while the test power source is connected to the terminate plate of the bushing.
Tg
δ
1
value changes in accordance with the temperature of the bushing’s body and, consequently, the
measured value must be divided by a correction factor given in the table 3 and a curve at the figure 3. In
this case it is presupposed that the mean temperature of the bushing body is calculated according to the
formula:
3
2
To
Ta
T
where:
T is the mean temperature of the bushing body;
Ta is the temperature of the surrounding air;
To is the temperature of the oil inside the transformer.
The result is corrected to the temperature of 20
0
C .
Table 3
Body temperature,
0
C
Correction factor for 20
0
C
10
1.20
20
1.00
30
0.85
40
0.77
50
0.75
60
0.75
70
0.82
80
0.90
Correction factor for dielectric dissipation factor tg
δ
of RIP
RIP body temperature (°C)
Figure 3
