Functions
4.1 Protection functions
3VL IEC molded case circuit breakers
44 System Manual, 11/2013, 110 0110 - 02 DS 03
Differential current protection with RCD module
The molded case circuit breaker with differential current protection is very often used to implement a
double function:
● Protection of systems against overload and short-circuit currents.
● Protection of cables and electrical equipment against damage from ground faults.
The SENTRON VL RCD modules are offered as accessories for the VL160X, VL160, VL250
and VL400 molded case circuit breakers with thermal-magnetic overcurrent releases. This
combination is called molded case circuit breaker with differential current protection of
type A. Type A means tripping is guaranteed both in the case of faults in sinusoidal
alternating currents and in the case of faults in pulsating direct currents. These units have an
adjustable trip time delay ∆t. The values for the rated fault current I
∆n
can also be adjusted.
In a fault-free system, the sum of the currents in the summation current transformer of the
RCD module is zero. A ground fault current occurring in the circuit as the result of an
insulation fault produces a differential current that induces a voltage in the secondary
winding of the current transformer. The evaluation electronics monitors the induced voltage
and transmit a trip command to the RCD trip unit if the trip criterion is met. The molded case
circuit breaker with differential current protection combination is designed to open he molded
case circuit breaker contacts if the differential current reaches a specific value.
Note
The RCD module can only be combined with 3VL molded case circuit breakers with thermal
-
magnetic overcurrent release. I
t cannot be combined with a molded case circuit breaker with
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