2021.06 / o
14
Electric Power Generation
Installation and maintenance
LSA 42.3
Low Voltage Alternator - 4 pole
4803 en -
4.5 - 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 (AVR may be
faulty)
- Field windings short-circuited
- Rotating diodes burnt out
- Revolving field coil 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
- 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/PMG : Voltage
between E+ and E– =
6V < UDC < 10V
- Check the speed (or AVR LAM set too high)
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)
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
(*)
During single-phase operation, check that the sensing wires from the AVR are connected to the correct output terminals
.
