Dead-Time Setting; De-Ionising Time; Minimum Fault Arc De-Ionising Time; Example Minimum Dead Time Calculation - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
• If the first fault is a single phase fault, a single pole autoreclose sequence will start,
• If the first fault is a multi phase fault, the first autoreclose sequence a three pole
autoreclose sequence will start.

5.10.1.2 Dead-time setting

At the end of the relevant dead time, the autoreclose single phase or three phase in progress
signal is reset and a CB close signal is given, provided system conditions are suitable. The
system conditions to be met for closing are that the system voltages are in synchronism or
dead line/live bus or live line/dead bus conditions exist, indicated by the internal check
synchronism element and that the circuit breaker closing spring, or other energy source, is
fully charged indicated from the DDB: 'CB Healthy' input. The CB close signal is cut-off
when the circuit breaker closes. For single pole autoreclose no voltage or synchronism
check is required as synchronising power is flowing in the two healthy phases. Check
synchronism for the first three phase cycle is controlled by a 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 (see specific section below);
• 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.
Should a single phase fault evolve to affect other phases during the single pole dead time,
the recloser will then move to the appropriate three phase cycle.

5.10.1.2.1 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:
Line Voltage (kV)
66
110
132
220
275
400
Table 14: Minimum fault arc de-ionising time (three pole tripping)

Example Minimum Dead Time Calculation

The following circuit breaker and system characteristics are to be used:
• CB Operating time (Trip coil energised → Arc interruption): 50ms (a);
For single pole autoreclose shot, the capacitive current induced from the
healthy phases can increase the time taken to de-ionise fault arcs.
Minimum De-Energisation Time (s)
0.1
0.15
0.17
0.28
0.3
0.5
P44x/EN AP/Hb6
(AP) 5-153