MarelliMotori MEC-100 Manuel De L'utilisateur page 69

3.7.3. Under-excitation limiter
The MEC-100 is capable of activating an under-excitation limitation function to avoid demagnetizing effects and losses of
synchronism during the paralleling operations. When this function is active (the activation results from the relevant
authorization), the MEC-100 senses the reactive power output (of demagnetizing type) and limits any consequent field current
reduction. The area of operation of the under-excitation limitation function is identified by a curve like that shown in Fig. 3.7.3.a.
In the figure, the dotted section is the area within which MEC-100 cannot operate; the limiter will intervene:
•
in PF mode by limiting the excitation current, to ensure that the working point remains inside the permitted area
•
in AVR mode, with Droop enabled, by just providing an external notification.
In both case, the limiter intervention is notified through a visual indication in the MEC-100 Interface System (blinking of the
Underexcitation Limiter item - see Para. 5.8.3); it can also be optionally associated with one of the two programmable output
relays. The limitation curve is obtained by linear interpolation between two point A and B (see example in Fig. 3.7.3.a,
percentage values refer to rated apparent power). The maximum underexcited reactive power values are given with Point A for
P=0 %, with point B for P = 100 % rated apparent power, in steps of 1 % from 0 % to 60 % of rated apparent power. For rated
apparent power, the calculated value in System Parameters tab (see Section 5).
The function can be enabled/disabled.
Q (Reactive P.)
3.7.4. Inrush current limiter
The MEC-100 is equipped with an internal protection against the so-called
maximum, instantaneous input current which appears when the device input stage is instantaneously energized. The limiter acts
only on the inrush current, while it has not any further influence on the normal working of the MEC-100.
3.8. PROGRAMMABLE RELAYS
The protection and limitation functions which can be set from MEC-100 Interface System can be individually associated to each
one of the two programmable relays provided with the MEC-100.
The provided contacts are normally open.
3.9. REACTIVE DROOP COMPENSATION
The MEC-100 provides a Reactive Droop Compensation function: it is used to obtain the desired distribution of the reactive load
between two or more generators which operate in parallel.
When the function is enabled, MEC-100 calculates the reactive part of the generator load, starting from the measurement of the
generator voltage between phases U and V and of the W phase current, and accordingly modifies the generator voltage
setpoint.
If the power factor is equal to one, the voltage setpoint will not be modified. An inductive (
reduction of the generator output voltage (Droop). A capacitive (
output voltage.
963857137_M
P
(Real P.)
B
100%
50%
0
0
Under-excitation Limitation Curve
A
50% 100%
Fig. 3.7.3.a
"
Inrush Current
" "
leading ) power factor results in an increase of the generator
MEC-100 – Marelli Motori
" " "
or Input Surge Current
" "
lagging ) power factor results in a
, that is the
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