Woodward
Manual MRI3-ITER GB
8
DOK-TD-MRI3 ITERE Rev.A
Figure 3.3: Earth-fault measuring by means of ring-core C.T. (IE)
When phase- and earth-fault current measuring are combined, the connection has to be realized as
per Figure 3.2 and Figure 3.3.
Voltage measuring for the directional detection:
Figure 3.4: Measuring of the phase voltages for the directional detection at earth-fault protection (IE> and IE>>).
3.1.1 Analogue input circuits
The protection unit receives the analogue input signals of the phase currents I
L1
(B3-B4), I
L2
(B5-
B6), I
L3
(B7-B8) and the residual current I
E
(B1-B2) each via separate input transformers. The con-
stantly detected current measuring values are galvanically decoupled, filtered and finally fed to the
analogue/digital converter.
