Blocking Schemes; Teed Feeder Applications - GE MiCOM P40 Agile Technical Manual

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Application Notes

MiCOM P40 Agile P442, P444

Figure 51 (i) shows the case where a short tee is connected close to another terminal. In this

case, zone 1 elements set to 80% of the shortest relative feeder length do not overlap. This

leaves a section not covered by any zone 1 element. Any fault in this section would result in

zone 2 time delayed tripping.

Figure 51 (ii) shows an example where terminal 'C' has no infeed. Faults close to this

terminal will not operate the relay at 'C' and hence the fault will be cleared by the zone 2

time-delayed elements of the relays at 'A' and 'B'.

Figure 51 (iii) illustrates a further difficulty for a PUP scheme. In this example current is

outfeed from terminal 'C' for an internal fault. The relay at 'C' will therefore see the fault as

reverse and not operate until the breaker at 'B' has opened; i.e. sequential tripping will occur.

Figure 51: Teed feeder applications

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.

Relay at C sees reverse fault until B opens

= area where no zone 1 overlap exists

Fault seen by A & B in zone 2

P44x/EN AP/Hb6