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the relay to pickup, then its effect can be increased by looping the conductor several
times through the toroidal transformer.
For Z either a resistor (30 to 500 Ω) or a capacitor (10 to 100 µF) in series with an
inrush-current-limiting resistor (approximately 50 to 100 Ω) is used. With correct con-
nections, the described circuit results in indications "U0> picked up", "3I0>
picked up" and finally "S/E/F TRIP" (LED 6).
Figure 3-20
Directional Check
If the current is supplied from a Holmgreen connection, the displacement voltage is
with Holmgreen
obtained in the same manner as in the above circuit. Only the current of that current
Connection
transformer which is in the same phase as the by-passed voltage transformer in the
delta connection is fed via the current path. In case of active power in generator direc-
tion, the same conditions apply for the relay - in principle - as with an earth fault in gen-
erator direction in a compensated network and vice versa.
7UM61 Manual
C53000-G1176-C127-3
Directional Check with Toroidal Transformers
3.3 Commissioning
283
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