GE P741, Technical Manual

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P74x/EN OP/Na7 Operation
(OP) 5-
28
MiCOM P741, P742, P743
OP
Only the second type of teleprotection is available within the P741 and P743, providing that
the corresponding hardware is fitted.
1.5.6.1 Protection signaling
In order to achieve fast fault clearance and correct discrimination for faults anywhere within a
high voltage power network, it is necessary to signal between the points at which protection
relays are connected. Two distinct types of protection signaling can be identified:
Unit protection Schemes:
In these schemes the signaling channel is used to convey analog data concerning the power
system between relays, typically current magnitude and/or phase.
Teleprotection - Channel Aided Schemes:
In these schemes the signaling channel is used to convey simple ON/OFF data (from a local
protection device) thereby providing some additional information to a remote device which
can be used to accelerate in-zone fault clearance and/or prevent out-of-zone tripping. The
InterMiCOM teleprotection provides the ideal means to configure the schemes in the
InterMiCOM relays, the selection will mainly depend on communications media availability,
system configuration, distances, cost issues and utility practice.
1.5.6.2 Definition of teleprotection commands
The decision to send a command is made by a local protective relay operation, and three
generic types of InterMiCOM signal are available:
Intertripping - In intertripping (direct or transfer tripping applications), the
command is not supervised at the receiving end by any protection
relay and simply causes CB operation. Since no checking of the
received signal by another protection device is performed, it is
absolutely essential that any noise on the signaling channel isn’t
seen as being a valid signal. In other words, an intertripping
channel must be very secure.
Permissive - In permissive applications, tripping is only permitted when the
command coincides with a protection operation at the receiving
end. Since this applies a second, independent check before
tripping, the signaling channel for permissive schemes do not have
to be as secure as for intertripping channels.
Blocking - In blocking applications, tripping is only permitted when no signal
is received but a protection operation has occurred. In other
words, when a command is transmitted, the receiving end device
is blocked from operating even if a protection operation occurs.
Since the signal is used to prevent tripping, it is imperative that a
signal is received whenever possible and as quickly as possible. In
other words, a blocking channel must be fast and dependable.