ABB REG316 4 Series Operating Instructions Manual page 261

REG 316*4 1MRB520049-Uen / Rev. F
where
I : rated current of the protected unit
GN
I , I : rated primary and secondary c.t. currents.
N1 N2
The current referred to the rated current I
I I
R GN
= = ´
i
R
I I
N N
The steady-state temperature rise becomes:
æ
I
GN
DJ = ´
ç
W
è I
N
At a constant current, the tripping time is:
æ
ç [ ]
J
%
ç 0
= t
t ln ç
ç
[ ]
J
%
ç
è
where
J
: initial temperature rise
0
J
: pick-up temperature rise
t
: thermal time constant.
The variables in the submenu 'DISPLAY OPERATING VALUES'
are the calculated temperature rise, the power dissipation and
the current. The first two are mean values over the period of
calculation (= t / 40).
The values shown in the event list is the power dissipation at the
instant of tripping.
Example:
Rated current of the protected unit
C.t. ratings
Rated relay current
I
N2
I
N 1
2
ö
I
N2
÷ ´
100%
I ø
N 1
ö
2
æ ö
I
÷
ç ç ÷ ÷
- ´
100
÷
I
è ø
B
÷
2
æ ö ÷
I
ç ç ÷ ÷
- ´
100
÷
I
è ø
ø
B
ABB Switzerland Ltd
of the protection is:
N
I = 8000 A
GN
I = 10000 A
N1
I = 5 A
N2
I = 5 A
N
3-223