MarelliMotori MJB 250 Betriebsanleitung Und Allgemeine Sicherheitshinweise Seite 17

FREQ
VOLT
PAR
USE OF POTENTIOMETERS
VOLT - Potentiometer for adjusting the output voltage of the generator.
It allows a wide range of voltage setting (i.e. between 350 and 450 V; or between 170 and 270 V depending on winding
connections). In case of resetting this potentiometer the voltage has to be set within 5% of the rated voltage of the machine.
In order to obtain a finer regulation, or to adjust the voltage from control panel or to limit the voltage range, it is possible to insert
an external potentiometer (see paragraph 5.2).
⇒ increase voltage
FREQ - Potentiometer for changing the low speed protection.
Usually it is set in order to reduce the excitation when the speed is 10 % below the rated value at 50 Hz. By removing the bridge
which is normally shorting terminals "60-Hz", the low speed protection acts properly for 60 Hz. In case of intevention, red led
switch on.
⇒ decrease frequency of intervention
AMP - Potentiometer for chancing the overexcitation limit device.
The limitation of overexcitation is an aid to protect the excitation system. This device intervenes (the yellow LED is switched on)
with a delay that does not regard the transitory condition. This protection device does not substitute the external protection
device.
⇒ increase the overexcitation threshold
To calibrate, bring the generator to the velocity, voltage, nominal load and rotate the AMP trimmer in an anticlockwise direction
until the protection is activated. (the yellow LED is switched on with a 10 sec delay). At this point rotate the trimmer in a
clockwise direction while not reaching a stable output voltage with the yellow LED switch on. Rotate again the trimmer in a
clockwise sense making sure the LED has not been switched off. In this position the protection acts when the overload is 15%.
In the workshop the potentiometer is set in the way the said limitation comes into operation only under extreme
overexcitation.
STAB - Potentiometer for stability adjust.
By rotating it clockwise stability increases, but response time becomes larger.
⇒ increase response time, increase stability
Use of microswitches
To change the stability characteristics of the regulator, it is possible to use the microswitches.
In such a way it is possible to insert capacitors on electronic stability circuit, then obtaining step changes in the transient response of
the regulator.
dip 1
⇒ speed response becomes slower
pos.ON
AMP STAB SLOPE
M O O
U U
T T
1 2
P
LED
GIALLO-YELLOW
Q
60
Hz
A
LED
B
ROSSO-RED
8
6
9 - + S6 S5 S4
OV
Varicomp Rilievo trifase
Tree phase
voltage reference
17
S3 S2 S1 - + N U
Alimentazione
Supply
Statore eccitatrice
Exciter stator
⇒ decrease voltage
⇒ increase frequency of intervention
⇒ decrease the overexcitation threshold
⇒ decrease response time, decrease stability
17
ENGLISH
1 2 3 4
MINI SWITCHES 1-4