Voltage Regulator; Thermal Protection Device; Rheostat For Remote Voltage Setting; Instructions For Manual Control Of Generators - MarelliMotori M8B 250 Instrucciones Y Advertencias De Seguridad

5. VOLTAGE REGULATOR

The generators are provided with automatic voltage regulator (AVR).
The AVR is provided with potentiometers to adapt the characteristics of the AVR to the different operating conditions.
The AVR is provided with adjustable stability circuitry to allow operations in a wide range of applications.
The AVR is equipped also with protecting circuit allowing the generator to operate underspeed if not loaded.
WARNING: it is not advisable to have the generator operating loaded when the frequency (speed) is below the rated value:
this kind of operation is an overload for the whole excitation system of the generator.
Radio interference suppressor
The voltage regulator is internally provided with radio interference suppressor, in order to limit the radio interference from the
generators M8B to within levels stated by C.E. standards for industrial areas.
Fuse
On the AVR there is a protecting fuse. In case it should be necessary to replace it, high speed fuses should be used; in addition
they should have high breaking resistance with a rated voltage of 250V, and rated current of 6.3 A.
Connection of AVR
The AVR is connected to the terminals of the generator and to exciter using FAST-ON terminals.
Use of potentiometers
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STAB - potentiometer for stability adjust decrease response time, decrease stability
⇒ increase response time, increase stability
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.
⇒ decrease frequency of intervention
VOLT - potentiometer for adjusting the output voltage of the generator.
It allows a wide range of voltage setting (i.e. between 350 and 470 V; or between 170 and 260 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.
⇒ increase voltage
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.

5.1. Thermal protection device

The generators are equipped with a thermal protection device against dangerous overloads. This device is connected to the auxiliary
terminals E-C, and can be used by the customer as command for either alarm or intervention. The terminals E-C have normally closed
contact for 250V - 5A.
This device does not act on regulation system (AVR).

5.2. Rheostat for remote voltage setting

For all generators, that rheostat can be inserted between the auxiliary terminals P and Q (FAST-ON terminals) of the AVR after having
removed the short-circuiting bridge. The external rheostat has to be inserted with its wiper in intermediate position and then the internal
potentiometer of AVR (VOLT) has to be reset to obtain the nominal voltage.

5.3. Instructions for manual control of generators

If the voltage regulator (AVR) breaks down, a manual control system can be used, when a 24 V D.C. power supply is available.
VOLT
FREQ
STAB
6.3 A-250
SUPERFAST FUSE
M25FA645A
ORANGE
VIOLET
VOLT
FREQ
STAB
PS
PS
P
P
Q
Q
Hz
Hz
60
60
VARICOMP
⇒ decrease response time, decrease stability
⇒ increase frequency of intervention
⇒ decrease voltage
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ENGLISH
V
Y
+
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SUPPLY
EXCITER FIELD
TERMINALS