Siemens 3VA1 100 A, Manual

Page: 53 / 532

Description
2.3 Technical details
3VA molded case circuit breakers
Manual, 04/2015, A5E03603177010-02
53
2.3.5 Current limitation
The term "current limitation" refers to the action of limiting the peak value of the prospective
impulse short-circuit current i
p
to a lower let-through current i
D
.
The compact design of the breakers has been made possible by their excellent current
limiting capabilities. In the event of a short circuit, the molded case circuit breaker
significantly reduces the magnitude of let-through current, i.e. it reduces the current loading
of downstream equipment (lower thermal load, fewer dynamic forces). The level of let-
through energy is also reduced to a considerable extent.
3VA molded case circuit breakers are designed with a current-limiting capability. IEC EN
60947-2 (VDE 0660-101), section 2.3, page 12, defines current-limiting molded case circuit
breakers in the following way:
"Circuit breaker that prevents the let-through current from achieving the prospective peak
value over a specific current range, and that limits the let-through energy (I
2
t) to a value that
is lower than the let-through energy of one half-wave of the symmetrical prospective current."
①
Unlimited current
②
Peak value of limited current
③
Limited current
i
D
Let-through current
i
p
Unlimited impulse short-circuit current
t
a
Break time