Different actions are taken depending on the severity of the internal fault. In case
of a temporary fault, the protection relay tries to recover from the situation by
restarting. Restarting varies per fault type. The restart procedure includes two
stages; when the relay detects a fault, it restarts itself in a few seconds after
the fault occurrence. If the relay did not recover after the first fast self-recovery
attempts (typically 1-2 restarts), or the fault reoccurs during the next 60 minutes,
the next self-recovery attempts (typically 3 restarts) are delayed for 10 minutes.
Exact recovery mechanism is described in
Table 26
. In case of a permanent fault, the
protection relay stays in the internal fault mode. All output relays are de-energized
and contacts are released for the internal fault. The protection relay continues to
perform internal tests during the fault situation. If the internal fault disappears,
the green Ready LED stop flashing and the protection relay returns to the normal
service state. Internal Fault: All ok event appears in the event list after succesfull
recovery.
One possible cause for an internal fault situation is a so-called soft error. The soft
error is a probabilistic phenomenon which is rare in a single device, statistically
not happening more often than once in a relay’s lifetime. No hardware failures are
expected and a full recovery from the soft error is possible by a self-supervision
controlled restart of the relay.
The self-supervision signal output operates on the closed-circuit principle. Under
normal conditions, the protection relay is energized and the contact gaps 3-5 in slot
X100 is closed. If the auxiliary power supply fails or an internal fault is detected, the
contact gaps 3-5 are opened.
Figure 12: Output contact
The internal fault code indicates the type of internal relay fault. When a fault
appears, the code must be recorded so that it can be reported to ABB customer
service.
1MRS757644 H
Basic functions
620 series
Technical Manual
69
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