Alstom MiCOM P54 Series, Technical Manual

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P54x/EN AP/La4 Application Notes
(AP) 6-74
MiCOM P543, P544, P545 & P546
AP
4.1.3.5 De-ionizing time
The de-ionization time of a fault arc depends on circuit voltage, conductor spacing, fault
current and duration, wind speed and capacitive coupling from adjacent conductors. As
circuit voltage is generally the most significant, minimum de-ionizing times can be specified
as in Table 30 below.
Note: For single pole high-speed auto-reclose, the capacitive current
induced from the healthy phases can increase the time taken to de-
ionize fault arcs.
Line voltage (kV) Minimum de-energization time (s)
66 0.1
110 0.15
132 0.17
220 0.28
275 0.3
400 0.5
Minimum Fault Arc De-Ionizing Time (Three Pole Tripping)
4.1.3.6 Example minimum dead time calculation
The following circuit breaker and system characteristics are to be used:
CB Operating time (Trip coil energized

Arc interruption): 50 ms (a);
CB O Reset time (Trip coil energized

Trip mechanism reset): 200 ms (b);
Protection reset time: < 80 ms (c);
CB Closing time (Close command

Contacts make): 85 ms (d).
De-ionizing time for 220 kV line:
280 ms (e) for a three phase trip. (560 ms for a single pole trip).
The minimum relay dead time setting is the greater of:
(a) + (c) = 50 + 80 = 130 ms, to allow protection reset;
(a) + (e) - (d) = 50 + 280 - 85 = 245 ms, to allow de-ionizing (three pole);
= 50 + 560 - 85 = 525 ms, to allow de-ionizing (single pole).
In practice a few additional cycles would be added to allow for tolerances, so Dead Time 1
could be chosen as

300 ms, and 1Pole Dead Time could be chosen as

600 ms. The
overall system dead time is found by adding (d) to the chosen settings, and then subtracting
(a). (This gives 335 ms and 635 ms respectively here).
4.1.3.7 Reclaim timer setting
A number of factors influence the choice of the reclaim timer, such as;

Fault incidence/Past experience - Small reclaim times may be required where there is a
high incidence of recurrent lightning strikes to prevent unnecessary lockout for transient
faults

Spring charging time - For high speed auto-reclose the reclaim time may be set longer
than the spring charging time. A minimum reclaim time of >5 s may be needed to allow
the CB time to recover after a trip and close before it can perform another trip-close-trip
cycle. This time will depend on the duty (rating) of the CB. For delayed auto-reclose
there is no need as the dead time can be extended by an extra CB healthy check AR
Inhibit Time window time if there is insufficient energy in the CB