MarelliGenerators MJB 160 Instructions Et Avertissements Pour L'installateur page 20

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 callabrate, 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
dip 2
⇒ speed response becomes slower
pos.ON
dip 3
⇒ speed response becomes slower
pos.ON
dip 4
⇒ standard low speed protection
pos.ON
SLOPE - Potentiometer for changing the slow speed protection characteristic slope.
With this potentiometer, we can increase or decrease the under speed ramp slope, and set the voltage droop for a fixed reduced
speed. Setting with SLOPE is possible only with dip 4 OFF.
⇒ increase voltage
PAR - Potentiometer for changing the droop
In order to obtain a correct sharing of reactive power, when two or more generators are required to operate in parallel, it is
necessary to verify that the no load voltage is the same, that the bridge between "A-B" is open and the voltage droop is the
same for all generators when loaded.
When this unit is inserted the output voltage should show a 4% voltage droop when passing from no load to full load 0.8 p.f.
If the voltage is increasing as the load increases, it is necessary to reverse the leads of the current transformer at the terminals
"A-B". If necessary, the voltage droop can be reset by acting on the internal potentiometer.
In single operation the terminals A and B have to be shorted.
⇒ increase droop
OV - Potentiometer for changing the overvoltage protection threshold.
In the event a overvoltage for the sensing loss or the SCR failure occurs, the A.V.R. is able to detect such overvoltage (red led
switch on ) and a low level is provided by an Open Collector output "OUT1".This device helps to monitor the excitation system.
The time delay is about 10 seconds. It has no automatic effect on the generator excitation system.
⇒ increase the overvoltage threshold
In factory the potentiometer is calibrated in order to exclude the overvoltage protection threshold. This control device
also if correctly calibrated has to be combined with an external protection system.
⇒ increase frequency of intervention
⇒ decrease the overexcitation threshold
⇒ decrease response time, decrease stability
⇒ proportional low speed protection V/f (see
pos.OFF
"SLOPE" potentiometer
⇒ decrease voltage
⇒ decrease droop
⇒ decrease the overvoltage threshold
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ENGLISH