Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 150/220 MiCOM P441/P442 & P444
4.5.11 Dead Timer Setting
High speed autoreclose may be required to maintain stability on a network with two or more
power sources. For high speed autoreclose the system disturbance time should be
minimised by using fast protection, <50 ms, such as distance or feeder differential protection
and fast circuit breakers <100 ms. For stability between two sources a system dead time of
<300 ms may typically be required. The minimum system dead time considering just the CB
is the trip mechanism reset time plus the CB closing time.
Minimum relay dead time settings are governed primarily by two factors:
•
Time taken for de-ionisation of the fault path;
•
Circuit breaker characteristics.
Also it is essential that the protection fully resets during the dead time, so that correct time
discrimination will be maintained after reclosure onto a fault. For high speed autoreclose
instantaneous reset of protection is required.
For highly interconnected systems synchronism is unlikely to be lost by the tripping out of a
single line. Here the best policy may be to adopt longer dead times, to allow time for power
swings on the system resulting from the fault to settle.
4.5.12 De-Ionising Time
The de-ionisation 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-ionising times can be specified
as in the Table below.
NOTE: For single pole HSAR, the capacitive current induced from the healthy
phases can increase the time taken to de-ionise fault arcs.
Line Voltage (kV) Minimum De-Energisation Time (s)
66 0.1
110 0.15
132 0.17
220 0.28
275 0.3
400 0.5
TABLE 14 - MINIMUM FAULT ARC DE-IONISING TIME (THREE POLE TRIPPING)