19
4.3 Basic design and method of operation
4.3.1 RCCB Type A
A residual current operated circuit breaker of Type A essentially consists of the
following function groups:
• Summation current transformer for residual current detection
• Tripping circuit with components for evaluation and holding magnet release
for converting the electrical measured variable into a mechanical latch release
• Breaker mechanism with contacts
Note:
With the exception of the tripping circuit, the design of the Type AC and Type F
RCCBs is identical to that of Type A.
The summation current transformer comprises all conductors of the circuit to be
protected, including the neutral conductor. In a fault-free system, the magnetic
effects of the current-carrying conductors are cancelled out in the summation
current transformer. There is no residual magnetic eld which could induce
voltage onto the secondary winding of the transformer.
A residual magnetic eld remains in the transformer core only if residual current
is owing, e.g. due to an insulation fault in the system to be protected (from
the electrical point of view, downstream of the residual current operated circuit
breaker). This generates a voltage in the secondary winding, effecting discon-
nection of the circuit with the excessive touch voltage by means of the holding
magnet release and the breaker mechanism (see gure 5).
Holding magnet
release
Mechanics of the
protective device
Secondary winding
Summation current transformer
Test button
Test resistor
Figure 5: Schematic representation of a residual current operated circuit breaker
To Next Page
Loading...
