The Aided DEF Forward setting determines the current sensitivity (trip sensitivity) of the aided DEF aided scheme.
This setting must be set higher than any standing residual current unbalance. A typical setting will be between
10% and 20% In.
The Aided DEF Reverse setting determines the current sensitivity for the reverse earth fault. The setting must
always be below the aided DEF forward threshold for correct operation of blocking schemes and to provide
stability for current reversal in parallel line applications. The recommended setting is 2/3 of the Aided DEF forward
setting.
Note:
The Aided DEF Reverse setting has to be above the maximum steady state residual current imbalance.
5.5
AIDED DEF POR SCHEME
The scheme has the same features and requirements as the corresponding Distance scheme and provides
sensitive protection for high resistance earth faults.
The signalling channel is keyed from operation of the forward DEF Fwd Set element. If the remote device has also
detected a forward fault, it operates with no additional delay when it receives this signal.
The logic is:
● Send logic: Key channel if DEF Fwd Set picks up
● Permissive trip logic: Trip if DEF Fwd Set picks up AND the channel key is received
The figure below shows the element reaches, and the simplified scheme logic of the Aided DEF POR scheme.
P543i/P545i Chapter 8 - Carrier Aided Schemes
P54x1i-TM-EN-1 231
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