Blocking Scheme Current Reversal Guard; Unblocking Logic (Permissive Scheme) - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-58
at substation D (circuit breaker D, Figure 36). The reset of the current reversal guard timer is
initiated when the reverse looking Zone 4 resets. A time delay tREVERSAL GUARD is
required in case the overreaching trip element at end D operates before the signal sent from
the relay at end C has reset. Otherwise this would cause the relay at D to over trip.
Permissive tripping for the relays at D and C substations is enabled again, once the faulted
line is isolated and the current reversal guard time has expired. The recommended setting is:
tREVERSAL GUARD =
Note:
3.2.5.2

Blocking Scheme Current Reversal Guard

The current reversal guard incorporated in the BOP scheme logic is initiated when a blocking
signal is received to inhibit the channel-aided trip. When the current reverses and the
reverse looking Zone 4 elements reset, the blocking signal is maintained by the timer
tREVERSAL GUARD. The relays in the healthy line are prevented from over tripping
because of the sequential opening of the circuit breakers in the faulted line. See Figure 36.
After the faulty line is isolated, the reverse-looking Zone 4 elements at substation C –circuit
breaker C) and the forward looking elements at substation D will reset. The recommended
setting is:
Where Duplex signalling channels are used:
tREVERSAL GUARD =
Where Simplex signalling channels are used:
tREVERSAL GUARD =
3.2.6

Unblocking logic (permissive scheme)

Two modes of unblocking logic are available with permissive schemes (blocking schemes
are excluded).
The unblocking logic issues (see section P44x/EN PL for DDB description):
• The Main and Directional Earth Fault alarm ('COS alarm' digital output),
• The internal Carrier Received signal (main distance or Directional Earth Fault
unblocking signal) (DDB 'DIST. UNB CR' or 'DEF. UNB CR').
The output DDBs 'COS alarm' and 'DIST. (or DEF.) UNB CR' depend on:
• The distance or DEF inputs signals: Carrier Received and Carrier Out of Service
inputs,
• distance and DEF channel-aided trip settings,
• Shared or independent logic between the DEF and Distance functions,
• Carrier Out of Service (COS) detected.
Three settings are available in the menu:
• None (basic mode). In this case, the opto input state is copied directly,
• Loss of Guard mode,
• Loss of Carrier mode.
3.2.6.1 None
The Logic equations for this mode are:
'COS alarm' = 'DIST. COS' + 'DEF. COS' (main alarm when carrier is out of service),
Maximum signal reset time + 35 ms.
The reverse guard begins when "reverse" falls and not when the directional is reverse
and immediately forward. It is validated if the directional becomes forward.
Maximum signalling channel operating time
+ 14 ms.
Maximum signalling channel operating time
- minimum signalling channel reset time
+ 14 ms.
Application Notes
MiCOM P40 Agile P442, P444