MarelliMotori MEC-20 Manuel Utilisateur page 28

9. DESCRIPTION
9.1. Setting generator voltage
The regulator is equipped with two single turn potentiometers for setting the generator voltage:
❖
VOLT, for coarse calibration of the voltage reference;
❖
VFINE for fine calibration of the voltage reference.
If initially positioned about midway, VFINE allows the generator voltage to be calibrated in a range of ±5% in
comparison to the voltage reference set with VOLT.
The generator voltage can be further changed using the external potentiometer (see Par. 9.5).
9.2. Under frequency limitation
The regulator performs a field current reduction every time the generator is used at low speed in order to prevent
overexcitation conditions that could damage the generator excitation system: in particular, the voltage reference is
automatically modified and decreased according to the curve shown in the following figure.
Volatge
V
NOM
0
f
The parameters that determine the curve and especially its slope are:
❖ The Corner Frequency (f
frequency value below which the regulator decreases the voltage reference.
❖ The Zero Volt Frequency (f
frequency related to the point where the reference is deleted. With f
of the under frequency curve.
9.3. Droop - Reactive droop compensation
The regulator is equipped with a "Reactive Droop Compensation" function whose purpose is to allow the desired
sharing of the reactive load between two or more generators operating in parallel.
When the function is enabled, through dip switch 2 - Block A (see Par. 8.3), the regulator calculates the reactive
part of the generator load, starting with the voltage sensing of the generator between phases U and V and the
current in phase W and consequently modifies the generate voltage reference.
A unit or capacitive power factor does not cause any change in the voltage reference. An inductive power factor
causes a generator output voltage reduction (Droop).
963857154_U
f
ZV C
), adjustable from 40 to 60 Hz using the FREQ potentiometer: it represents the
C
), adjustable from 0 to 40Hz using the SLOPE potentiometer: it represents the
ZV
f Frequency
NOM
set, calibration of d
C
Legenda:
V Nominal Voltage
NOM
f Zero Volt Frequency
ZV
f Corner Frequency
C
f Nominal Frequency
NOM
determines the slope
ZV
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