21/07/2010
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MRAR 01/96 C
5.3 Functional Sequence
To understand this chapter completely it is advised that paragraphs 4.1 and 4.2 should be read first.
5.3.1 Switching on the MRAR Relay
If the circuit breaker to be supervised is in the off position while switching on the MRAR, the unit
changes to the Inactive state when applying the auxiliary voltage. The OK LED on the front panel is not
lit and the unit is not ready for auto reclosing. If, however, the circuit breaker is in the on position when
applying the auxiliary voltage, the unit changes to the Reclaim Time state and remains blocked for this
period (from 1 to 300 seconds adjustable). This is indicated by the tr LED. After the Reclaim Time has
elapsed the unit changes to the Ready state and auto reclosing may now be carried out. The OK LED
indicates this state.
5.3.2 Switching on the Circuit Breaker Manually
If the circuit breaker is switched manually to an un-faulted line, first the unit will remain blocked for the
Reclaim Time (adjustable 1 - 300 seconds) and then changes to the Ready state. If the circuit breaker is
switched manually to a faulted line then the breaker is switched off by the associated protection unit.
The MRAR then remains in the Inactive state and reclosing is not possible.
5.3.3 Switching off the Circuit Breaker Manually
When switching off the circuit breaker manually, the unit changes at once from the Ready state to the
Inactive state. The OK LED extinguishes and reclosing is not possible.
5.3.4 Starting Auto-Reclosing
When signals are applied to the Protection Energising or the Protection Tripping inputs, 21 and 27, the
unit changes from the Ready to the Starting state. The RUN LED illuminates and the fault timer (tf
adjustable from 0.01 to 2.05 s) begins to time out. A tripping timer (set at 0.2 s) is started when the
mains protection tripping command takes place before the fault timer has timed out. The "Start
requirements not fulfilled" is evaluated and the MRAR is locked out for the duration of the Reclaim
Time if there is a difference between the Mains Protection Energised/Tripped and the set Fault Time. If
the Circuit Breaker OFF signal occurs before the tripping timer has timed out, it is evaluated as a "Start
Condition Fulfilled" and the unit changes to the Cycle state. If, however, the OFF signal does not occur
before the tripping timer has timed out, it will be evaluated as "Start Condition Not Fulfilled" and the
unit is locked out for the duration of the set Reclaim Time.
5.3.5 Reclosing Without Success
After the start condition has been fulfilled the unit changes to the Cycle state and the Dead Time, tD, is
started. The MRAR can be programmed to reclose between one and four times and for each reclosing a
Dead Time has to be set, (tD1 = 0.1 - 20 s, tD2 - tD4 = 0.2 - 99.9 s). When the Dead Time has expired
and all other reclosing conditions have been fulfilled, the switch on command is given to the Circuit
Breaker. The switch on command will remain as long as the On signal to the Circuit Breaker or the
setting of the On Impulse Timer (adjustable between 0.05 - 9.99 s). With the beginning of the switch on
command the Reclaim Timer is started. When a new OFF signal, not a fault signal, to the circuit breaker
appears during the Reclaim Time, a reclosing has taken place without success. The unit then changes
from the Cycle state to the Blocked state and the RUN LED extinguishes with the LO and O
→
I LED's
being illuminated.
