MarelliMotori D-Vo Light Manuel D'utilisation page 30

Loss of sensing (LOS)
Diode monitoring (DMS)
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D-Vo can sense the overexcitation conditions due to loss of voltage sensing at
the regulator sensing terminals and issue an alarm warning, in less than 1s.
In particular, D-Vo, through an internal hardware system, can distinguish
between the loss of one or more sensing connections and the cases in which
the sensing voltage is null due to any operating conditions of the generator (like
an output terminal short-circuit).
The switching of the protection to active state is signalled by a visual warning in
D-Vo Dashboard, and can be optionally associated with one of the three
programmable output relays (which assumes the same state as the protection).
The loss of sensing protection can directly operate on the regulation, according
to one of the following modes, selected in advance through D-Vo Dashboard:
•
Shutdown: D-Vo instantaneously shuts down the generator;
•
Transfer to FCR: D-Vo performs the automatic transfer to the FCR mode,
providing an excitation current whose value matches the one set in the
Setpoint tab of D-Vo Dashboard.
D-Vo exits the active alarm state if and only if the cause of the protection tripping
has been eliminated and an ALARM RESET is performed.
The function can be enabled/disabled.
D-Vo can sense any abnormal excitation currents due to the failure of one or
more diodes of the rotating three-phase rectifier bridge of the generator, in case
of both diode open circuit and diode short-circuit. The currents in question could
result in damages to one or more generator components: for example, a diode
short-circuit causes a very intense current to flow into the exciter armature
winding, overheating and damaging the exciter. A diode open circuit, instead,
causes an increase in the excitation constantly requested to the voltage regulator
to maintain the operating level, potentially damaging the regulator.
To monitor the state of the rotating rectifier bridge diodes, D-Vo performs an
analysis of the excitation current and of its ripple. The figure shows an example
of how the current waveform changes in case of a diode failure.
Under normal operating conditions, the excitation current has a ripple overlapping
the continuous value, which significantly increases in case one or more diodes
should fail.
In case of diode short-circuit, the ripple is very high and certainly higher than the
one resulting from a diode open circuit.
D-Vo allows to set two alarm thresholds, called Low Level of failure and High
Level of failure.
The two thresholds can be set in such a way as to distinguish between a slight or
medium failure (like a diode open circuit) and a heavy or dangerous failure (diode
short-circuit).
The two levels, in fact, can be set as follows:
•
When the excitation current ripple is below the first settable threshold (Low
Level), the rotating rectifier bridge is assumed to be intact.
•
When the excitation current ripple rises above the first settable threshold
(Low Level), for a settable T
Level, the Diode Failure - Low Level protection shall trip. This rectifier bridge
failure does not cause any damage to the generator and to its component
parts in the short term, but must be resolved anyway.
•
When the excitation current ripple rises above the second settable threshold
(High Level), for e settable T
protection shall trip. This condition shall be regarded as a critical failure which
can damage the generator and its component parts in the short term.
The switching of the Diode Failure - Low Level protection to active state is
signalled by a visual warning in D-Vo Dashboard, and can be optionally
associated with one of the three programmable output relays (which assumes the
same state as the protection).
The switching of the Diode Failure - High Level protection to active state is
signalled by a visual warning in D-Vo Dashboard, and can be optionally
D-Vo Light – Marelli Motori
time delay, while remaining below the High
DL
time delay, the Diode Failure - High Level
DH
EN 30