Areva MiCOM P441, Technical Manual

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Application Notes P44x/EN AP/E33
MiCOM P441/P442 & P444 Page 105/220
3.2.4 Blocking Schemes
Blocking schemes are particularly suited to the protection of teed feeders, since high speed
operation can be achieved where there is no current infeed from one or more terminals. The
scheme also has the advantage that only a common simplex channel or a triangulated
simplex channel is required.
The major disadvantage of blocking schemes is highlighted in Figure 63 (iii) where fault
current is outfeed from a terminal for an internal fault condition. relay 'C' sees a reverse fault
condition. This results in a blocking signal being sent to the two remote line ends, preventing
tripping until the normal zone 2 time delay has expired.
3.3 Alternative setting groups
The P441, P442 and P444 relays can store up to four independent groups of settings. The
active group is selected either locally via the menu or remotely via the serial
communications. The ability to quickly reconfigure the relay to a new setting group may be
desirable if changes to the system configuration demand new protection settings. Typical
examples where this feature can be used include:
Single bus installations with a transfer bus;
Double bus installations, with or without a separate transfer bus, where the transfer circuit
breaker or bus coupler might be used to take up the duties of any feeder circuit breaker
when both the feeder circuit breaker and the current transformers are by-passed.
In the case of a double bus installation, it is usual for bus 1 to be referred to as the main bus
and bus 2 as the reserve bus, and for any bypass circuit isolator to be connected to bus 2 as
shown in Figure 64. This arrangement avoids the need for a current polarity reversing switch
that would be required if both buses were to be used for by-pass purposes. The standby
relay, associated with the transfer circuit breaker or the bus coupler, can be programmed
with the individual setting required for each of the outgoing feeders. For bypass operation
the appropriate setting group can be selected as required. This facility is extremely useful in
the case of unattended substations where all of the switching can be controlled remotely.
Feeder 1
21 21
21
Feeder 2
P3077ENa
Main bus
Reserve bus (2)
P440
(1)
FIGURE 64 - TYPICAL DOUBLE BUS INSTALLATION WITH BYPASS FACILITIES
A further use for this feature is the ability to provide alternative settings for teed feeders or
double circuit lines with mutual coupling. Similar alternative settings could be required to
cover different operating criteria in the event of the channel failing, or an alternative system
configuration (ie. lines being switched in or out).