MarelliMotori MEC-100 Manual De Instrucciones página 65

3.6.5. Generator Over-current Protection
The MEC-100 is capable of monitoring the value taken by the generator stator current under load conditions and sending a
warning when the current value exceeds a predefined limit for a pre-established time interval; this time interval can be derived
from a curve of the type shown in Fig. 3.6.5.a. All of that before the over-current causes a generator overheating/failure. The
characteristic curve is calculated starting from the determination of a maximum continuative current level (given in percentage
compared with the generator rated current value, with values included between 0 and 110%, and minimum increase of 1%), a
current reference level (expressed in percentage compared with the generator rated current value, with values included
between 0 and 120%, and minimum increase of 1%) and a minimum operation time value (time delay from 0 to 3600s, minimum
increase of 1s) associated to the reference level.
Maximum
Current
Maximum
Continuative
Current
When the stator current value exceeds the maximum continuous current value, the generator over-current protection is
activated by a warning signal after a time interval depending on the generator current value which has been reached, according
to the curve of Fig. 3.6.5.a.
Higher the over-current, shorter the operation time (time delay). The activation of this protection is accompanied by a visual
warning in the MEC-100 Interface System (Generator Overcurrent Protection item flashing, see Par. 5.8.3), and optionally can
be associated to one of the two programmable output relays. This function can be enabled/disabled.
3.6.6. Loss of Sensing Protection
The MEC-100 is capable of sensing the over-excitation conditions resulting from the loss of voltage sensing and coming into
operation by a warning signal in less than 1s. In particular, the protection detects the loss of one or more wires of the sensing,
via a hardware solution, that allows to discriminate the cases in which the sensing voltage is zero due to operating conditio ns of
the generator (eg. short circuit).
The activation of this protection is accompanied by a visual warning in the MEC-100 Interface System (Loss of Sensing
Protection item flashing), and optionally can be associated to one of the two programmable output relays. The Loss of Sensing
protection can directly operate one of the two following actions (preliminary choice is required, see Par. 5.7.8):

Shutdown: the MEC-100 operates the instantaneous de-excitation (shutdown) of the generator.

FCR: the MEC-100 automatically changes over to FCR mode, supplying the excitation current value set in the Setpoint
window (see Par. 5.7.3.).
This function can be enabled/disabled.
WARNING: Any activation of the protection when it is enabled will cause an excitation shutdown or a
change over to the FCR mode. Before enabling the protection, please make sure that the choosen
protection option is not dangerous for the plant or the network to which the generator is connected.
963857137_G
I
Time
Delay
Fig. 3.6.5.a
Generator Over-current Protection Curve
MEC-100
t
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