ABB REX 521 Technical Reference Manual, Standard Configurations page 138

REX 521
138
Protection Relay
Technical Reference Manual, Standard Configurations
In the following example two auto-reclosures initiated by the start of the protection
are carried out. The auto-reclosures are subject to a preset start-delay time initiated
from the start signal of the protection.
The first auto-reclosure (see Fig. 9.4.3.1.-1) is delayed only slightly to avoid
unwanted auto-reclosures (100 ms). Shot 1 is a high-speed auto-reclosure (short
dead-time 300 ms) mainly used for extinguishing the arc at the fault place. Before
the second shot is initiated, a longer start delay time is used to attempt to burn the
fault (300 ms). The dead time of the Shot 2 is long, a so called delayed auto-
reclosure, that typically lasts minutes (in this case 2 min). Should the fault still
persist when Shot 2 has been performed (after 200 ms), a final circuit-breaker
tripping will follow and a DEFTRIP alarm signal is received and the contact alarms
if needed.
The operate time of the protection is longer than the operate times of the auto-reclose
function and the final trip time. Therefore the protection operates as a back-up for
the auto-reclose function, if the tripping carried out by the auto-reclose function
fails.
Instant of fault
AR1
(Start signal
from protection)
Trip
Circuit breaker
Shot 1
Start
delay
0.1 s
Open signal
Close signal
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An auto-reclose sequence can also be initiated by the trip signal of a protection
function (see Fig. 9.4.3.1.-2). The trip signal from the protection trips the breaker
after the set start-time of the protection function.
When the set dead-time of the auto-reclosure function elapses, the function closes
the circuit breaker and a discriminating time (TDDUE output signal) is started. If
one of the initiation signals is activated during the discriminating time, and if the
short circuit current or the earth fault current increases and the operate time of the
protection function shortens at inverse-time operation, the AR shots are prevented
and a definite tripping will follow. The discriminating time (td) can be set out of use
by selecting the value 0. Normally, this discriminating time is shorter than the
operate time of the protection function, so the sequence is allowed to continue with
the second shot, the third shot, and so on, until the selected sequence has been
completed or the fault has disappeared.
Shot 2
Start
delay
0.3 s
Shot 1 Shot 2
Dead time
Dead time
0.3 s 120 s
1MRS 751802-MUM
Shot 3
Start
delay
0.2 s