Functions
4.1 Protection functions
3VL IEC molded case circuit breakers
50 System Manual, 11/2013, 110 0110 - 02 DS 03
Ground fault detection in unbalanced systems
The neutral conductor current is measured directly. Only the ground-fault current is
measured for the 3-pole circuit breakers. In the case of the 4-pole circuit breakers, the
neutral conductor overload protection is also measured.
The overcurrent release calculates the ground-fault current using the vectorial summation of
the three phase currents and the neutral conductor current.
The 4th current transformer of the neutral conductor is installed internally in the case of 4-
pole molded case circuit breakers.
Figure 4-6 3-pole molded case circuit breaker, current transformer in neutral conductor current
Figure 4-7 4-pole molded case circuit breaker, current transformer installed internally
Measurement method 2: Direct detection of the ground-fault current via a current transformer in the
grounded neutral point of the transformer
The current transformer is installed direct in the grounded neutral point of the transformer.
Figure 4-8 3-pole molded case circuit breaker, current transformer in the grounded neutral point of
the transformer
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