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4.6 REMOTE OPEN DETECTOR UNIT (ROD) (MLP3000)
The remote open detector unit operates when the breaker on the remote side
opens during an unbalanced internal fault. This characteristic allows the accelerated
isolation of faults. In the absence of this unit, a sequential trip will be provoked.
In this Way it allows a rapid trip in the local extreme, for faults inside the line but
outside zone 1 reach without using a communications carrier. For example, let's see how a
fault is cleared in 95% of the line:
The local relay will detect the fault in zone 3 and start the zone 3 and zone 2 timers.
Meanwhile the remote extreme detects the fault in zone 1 and orders a trip. When the
remote breaker has been opened, it is detected by the local relay and once the ROD timing
has terminated a remote open detector trip is performed.
We need to keep in mind that if the tripping time plus the time to open the remote
breaker plus the ROD timing is greater then the zone 2 timing, the local relay will perform a
zone 2 trip and not a ROD trip. For ROD timing keep in mind that ROD units as well as
distance measuring units take 1 cycle to operate.
This unit does not work for three phase faults, since the information to detect that
the remote extreme is open reaches the local extreme through a vectoral change of t]1C
line current in any of the "healthy" phases.
Figures 8.1 and 8.2 illustrate the algorithm for remote open pole detection. This
algorithm is based on the fact that the impedance of a "healthy" line whose extreme remote
is open is purely capacitive.
4.7. DISTURBANCE DETECTION UNIT (DD) (MLP3000)
This function assists in the detection of a fuse failure and the starting of the
oscillographic register. Its purpose is to detect faults before they are detected by the
distance measuring units, based on the detection of the fault positive sequence current.
Figures 9.1 and 9.2 illustrate the algorithm for disturbance detection.
GEK-98846A
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