113
G20, 30, 40 SIIIA Operation & Maintenance Manual
ELECTRICAL FAULTS
FAULT
ACTION
EFFECT
CHECK / CAUSE
No voltage at
no load on
start-up
Connect a new battery of 4
to 12 volts to terminals E-
and E+, respecting the
polarity, for 2 to 3 seconds
The alternator builds up and its
voltage is still correct when the
battery is removed
- Lack of residual magnetism
The alternator builds up but its
voltage does not reach the rated
value when the battery is removed
- Check the connection of the
voltage reference to the AVR
- Faulty diodes
- Armature short-circuit
The alternator builds up but its
voltage disappears when the battery
is removed
- Faulty AVR
- Field windings open circuit (check
winding)
- Revolving field coil open circuit
(check the resistance)
Voltage too
low
Check the drive speed
Correct speed
Check the AVR connections
(possible AVR failure)
- Field windings short-circuited
- Rotating diodes burnt out
- Main field winding short-circuited
- Check the resistance
Speed too low
Increase the drive speed (do not
touch the AVR voltage pot. (P2)
before running at the correct speed)
Voltage too
high
Adjust AVR voltage
potentiometer
Adjustment ineffective
Faulty AVR
Voltage
oscillations
Adjust the AVR stability
potentiometer
If no effect: try normal or fast stability
modes (ST2)
- Check the speed: possibility of
cyclic irregularity
- Loose connections
- Faulty AVR
- Speed too low when on load (or
AVR LAM set too high)
Voltage
correct at no
load and too
low when on
load
(*)
Run at no load and check
the voltage between E+
and E- on the AVR
AREP: Voltage between E+ and E-
= 6V < UDC < 10V
- Check the speed
SHUNT: Voltage between E+ and E-
= 10V < UDC < 15V
- Faulty rotating diodes
- Short-circuit in the revolving field
coil. Check the resistance.
- Faulty exciter armature. Check the
resistance.
(*) Warning : During single-phase operation, check that the sensing wires from the AVR are connected to the
correct output terminals.
Voltage
disappears
during
operation
(**)
Check the AVR, the surge
suppressor, the rotating
diodes, and replace any
defective components
The voltage does not return to the
rated value
- Exciter winding open circuit
- Faulty exciter armature
- Faulty AVR
- Revolving field coil open circuit or
short-circuited
(**) Warning : The AVR internal protection may cut in (overload lost connection, short circuit).
Summary of Contents for G20 SIIIA
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