Reassembly Operations; Voltage Regulator "Mark I - MarelliGenerators MJB 250 Instructions

For two bearing generators:
- remove the half coupling from shaft extension and remove the key (223)
- remove the bolts fixing the inner D-end bearing cap (131) to the shield.
- remove the bolts fixing the shields (4-5) to the frame, then remove the shields having care to sustain the rotor in order it will
not fall heavily on the stator
- using proper lifting means, remove the rotor (3) from the main stator, through the D.E. side, taking special care to avoid any
damage to the windings.
For single bearing generators:
- remove the bolts fixing the N.D.E. shield (5) to the frame and dismantle the shield
The rotor can be extracted from the stator, from D.E. side.
It should be remembered that the exciter stator is fixed to the N.D.E. endshield: special care should be taken to avoid
ATTENTION! :
any damage to its windings when removing the N.D.E. shield; furthermore be sure the connections or the exciter stator are free to slide
out from terminal box.
If a bearing needs to be replaced, remove it with a suitable puller.

4.4. Reassembly operations

Carry out the operations described above for dismantling in reverse order. If the end-shield have been removed, the fixing screws have
to be fixed with LOCTITE type 242 (on the threaded surface).
If a bearing was removed, always install a new one.
To make assembly easier, the bearings should be heated to about 80 °C.
: bearings should be assembled with the utmost care in order not to damage them.
ATTENTION!
If a locking element has to be replaced, make sure that the new one is of the same type and same resistance class of the original.
The fallowing table indicates the tightening torques valid for locking screws and nuts:
Application
Fixing of electrical connections
Fixing of components (endshields, bearing caps, etc).
Fixing of feet or flange.
5. VOLTAGE REGULATOR "MARK I" ( M40FA640A/A)
The generators are provided with automatic voltage regulator (AVR) "MARK I" (M40FA640A/A).
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.
it is not advisable to have the generator operating loaded when the frequency (speed) is below the
ATTENTION!:
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 MJB 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 500V, and rated current of 10A.
Connection of AVR
The AVR is connected to the terminals of the generator and to exciter using FAST-ON terminals.
when changing generator wiring diagram, it is advisable to pay attention to connection of AVR, in order to
ATTENTION!:
avoid AVR damages.
18
Tightening torques in Nm
M 5 M 6 M 8
2.5 4 8
5 8 22
18
Thread diameter
M 10 M 12 M 16 M 20
12 20 40 /
45 75 180 350
ENGLISH
M 24 M 27
/ /
620 900