ABB REX 521 Technical Reference Manual, Standard Configurations page 161

1MRS 751802-MUM 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 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 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), the final circuit-breaker
tripping will follow and a DEFTRIP alarm signal is received (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. Thus 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. 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 definite tripping will follow. The discriminating time, usually called 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
REX 521
Shot 3
Start
delay
0.2 s
161