Technical information

4/2
Ip [kA]
x I
rms
[kA]
10
10
1
1
10
2
10
3
10
2
10
3
50 kA
36.5 kA
13.5 kA
160 A
t [s]
x I
1
10
10
-1
10
-2
10
2
1
10
10
2
10
3
10
4
1
10
-1
107.9 s
31.5 s
7.0 s
3 x I
1
I
2
t [10
6
A
2
s]
x I
rms
[kA]
10
10
-1
10
-2
1
10
1
10
2
10
3
20 kA
160 A
1SDC210033D0202
Examples of Curve reading
Example 3 – XT2N 160
Limitation curves
The figure below gives the trend of the Limitation curves of the
XT2N 160 In=160 A circuit-breaker.
The effective value of the prospective symmetrical short-circuit cur-
rent is given on the abscissas of the diagram, whereas the peak value
of the short-circuit current is indicated on the ordinates.
The limiting effect can be evaluated by comparing the peak value
corresponding to the prospective short-circuit current (curve A) with
the peak limited value (curve B), at the same value of symmetrical
short-circuit current.
For a fault current of 20 kA, the XT2N 160 circuit-breaker with a
thermomagnetic trip unit In =160 A limits the peak prospective
short-circuit current to 13.5 kA at a voltage of 500 V, with a reduc-
tion in relation to the peak value of the prospective short-circuit
current of 36.5 kA.
Example 1 – XT3N 250
Trip curves for distribution
(thermomagnetic trip unit)
Let us consider an XT3N 250 TMD In=250 A circuit-breaker.
According to the conditions the overload is found in, i.e. with the
circuit-breaker at thermal regime or not, tripping of the thermal
protection varies considerably.
For example, for an overload current 3xI
1
, the trip time is between
107.9 s and 31.5 s for cold tripping and between 31.5 s and 7.0 s
for hot tripping.
For fault current values higher than 2500 A the circuit-breakers trips
with the instantaneous magnetic protection I
3
.
Example 2 – XT2N 160
Specific let-through energy curves
The following figure shows an example of the graph of the specific
let-through energy of the XT2N 160 In=160A circuit-breaker at a
voltage of 220/230 V.
The prospective symmetrical short-circuit current is indicated on
the abscissas, whereas the values of the specific let-through energy
expressed in A
2
s are shown on the ordinates.
The circuit-breaker lets through a value of I
2
t equal to 0.76 · 10^6 ·
A
2
s in correspondence with a short-circuit current of 20 kA.
A curve
B curve