ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-224
The temperature rise measured by the protection at a rated
current of I
GN
is:
DJ
W
=´
æ
è
ç
ö
ø
÷
´=
8000
5
5
10000
100% 64%
2
The settings for overtemperatures of 5% and 10% respectively
are:
Theta-Warn = 67%
Theta-Trip = 70%
Normally the protection is configured such that the initial tem-
perature rise is 100 % (‘Theta-Begin’ = 100 %).
With I
B
adjusted, the settings become:
Base current:
I
I
I
I
I
I
B
N
GN
N
N2
N
=´= ´ =
1
8000
5
5
10000
08.
The settings for alarm and tripping are then:
Theta-Warn = 105%
Theta-Trip = 110%
Transformers have two distinct exponential functions, one for the
oil and one for the winding. The corresponding mean values are:
Oil :
DJ
oil
= 50 K t
oil
= 120 min
Winding :
DJ
W
- DJ
oil
= 10 K t
W
= 10 min
The total temperature rise of the winding is thus
DJ
W
= 60 K.
Since however the model operates with just a single exponential
function, its temperature rise has to follow the best possible
equivalent exponential function as shown in Fig. 3.5.23.1. The
steady-state temperature rise of this equivalent function is
identical to the total temperature rise of the winding, i.e.
DJ
W
=
60 K in the example above. Its time constant, however, is
typically 60 to 80% of the temperature rise of the oil (see Fig.
3.5.23.2).
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