Setting Guidelines; De-Ionising Time Guidance; Dead Timer Setting Guidelines; Example Dead Time Calculation - GE P4A Technical Manual

P54A/B/C/E
6

SETTING GUIDELINES

6.1

DE-IONISING TIME GUIDANCE

The de-ionisation time of a fault arc depends on several factors such as circuit voltage, conductor spacing, fault
current and duration, atmospheric conditions, wind speed and capacitive coupling from adjacent conductors. For
this reason it is difficult to estimate the de-ionisation time. Circuit voltage is, generally the most significant factor
and experience tells us that typical minimum de-ionising times for a three-phase fault are as follows:
66 kV: 100 ms
●
110 kV: 150 ms
●
132 kV: 170 ms
●
220 kV: 280 ms
●
● 275 kV: 300 ms
400 kV: 500 ms
●
Where single-pole high speed Autoreclose is used, the capacitive current induced between the healthy phases and
the faulty phase tends to maintain the arc. This significantly increases the de-ionisation time and hence required
dead time.
Single-pole Autoreclose is generally only used at transmission voltages. A typical de-ionisation time at 220 kV may
be as high as 560 ms.
6.2

DEAD TIMER SETTING GUIDELINES

High speed Autoreclose may need 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 (typically <30 ms)
and fast circuit breakers (typically <60 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 circuit breaker) is the trip mechanism reset time plus the
circuit breaker closing time.
The Autoreclose minimum dead time settings are governed primarily by two factors:
Time taken for de-ionisation of the fault path
●
Circuit breaker characteristics
●
It is essential that the protection fully resets during the dead time, so that correct time discrimination will be
maintained after Autoreclose 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 resulting from the fault to settle.
6.2.1

EXAMPLE DEAD TIME CALCULATION

The following circuit breaker and system characteristics can be used for the minimum dead time calculation:
a) Circuit breaker Operating time (Trip coil energized to Arc interruption): 50 ms
●
b) Circuit breaker Opening + Reset time (Trip coil energized to trip mechanism reset): 200 ms
●
● c) Protection reset time: < 80 ms
d) Circuit breaker Closing time (Close command to Contacts make): 85 ms
●
● e) De-ionisation time (280 ms for 3-phase, or 560 ms for 1-phase)
Three-phase de-ionisation time for 220 kV line is typically 280 ms.
The minimum Autoreclose dead time setting is therefore the greater of:
(a) + (c) = 50 ms + 80 ms = 130 ms, to allow protection reset
P54xMED-TM-EN-1
Chapter 7 - Autoreclose
179