Seg HighTECH Line - Page 5

TD_MRI1_06.05_GB 5
3 Design
3.1 Connections
Phase and earth current measuring:
Figure 3.1: Measuring of the phase currents for over-current-
and short-circuit protection (I>,I>>)
Figure 3.2: Earth-fault measuring by means of ring-core C.T. (I
E
)
When phase-- and earth-fault current measuring are
combined, the connection has to be realized as per
Figure 3.1 and Figure 3.2.
Figure 3.3: Phase current measuring and earth-current
detection by means of Holmgreen-circuit.
This connection can be used with three existing phase
current transformers when combined phase and earth-
current measuring is required.
Disadvantage of holmgreen-circuit:
At saturation of one or more C.Ts the relay detects
seeming an earth current.
* This arrow shows the current flow in forward direction, for this LED →← lights up green