Lister Petter T Series, Operator'S Handbook Manual

Page: 53 / 81

8
ALTERNATOR OpERATORS' hANdbOOk
SERVICE ANd mAINTENANCE
WARNING
Service and fault-finding can be
hazardous and can result in personal
injury and/or equipment damage if
done incorrectly. Only qualified
personnel should carry out such
work.
As part of routine maintenance, periodic
attention to winding condition and
bearings is recommended.
WINdING CONdITION
The condition of the windings can
be assessed by measurement of
insulation resistance to earth.
The AVR should be disconnected
during this test and the resistance
temperature detector leads grounded.
The insulation resistance to earth of
all windings should be in excess of
1.0M Ω.
Should the insulation resistances be
less than these values then drying out
the generator windings is essential.
Drying out may be carried out by
directing warmed air into the alternator
air inlets.
Alternatively, the main stator windings
may be short-circuited with a bolted
three-phase short at the main terminals
and the generating set run with the
AVR disconnected. A DC supply is
connected to the leads removed from
the AVR (Ensuring correct polarity). The
DC supply must be variable between
0-24V and capable of supplying 1.0A.
An AC ammeter is required to measure
the winding lead current.
Set the DC voltage to 0V. Start the set
and slowly increase the DC voltage to
pass current through the winding. The
current level should not exceed the
rated current of the alternator. Normally
- 1 hour should be sufficient to dry the
winding by this method.
The short circuit must not be applied
with the AVR in the circuit. Excess
current will damage the windings.
After drying out the insulation resistance
should be re-checked to verify the
value above has been exceeded. It
is recommended that the insulation
resistance is checked as below.
Separate the neutral leads:
Ground V
and W
Phase and
Megger
U phase to
ground
Ground U
and W
Phase and
Megger
V phase to
ground
Ground U
and V
Phase and
Megger
W phase to
ground
bEARING CONdITION
All bearings are sealed for life and are
not re-greasable. During overhaul,
seals should be checked and bearings
replaced as necessary or in any event
after 40000 hours service.
fAULT fINdING AVR
No voltage
build-up when
starting set
1) Check speed
2) Check residual voltage
3) Check excitation test
procedure.
Unstable voltage
on/off load
1) Check stability
2) Check stability setting
High voltage
on/off load
1) Check speed
2) Check load is not capacitive
Low voltage
off load
1) Check speed
2) Check link 1-2 or hand
trimmer for continuity