PI Manufacturing AC generators - Manual (Page 26)

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
If the minimum value of 1.0M
Ω is not obtained, drying out
must be continued and the test repeated. 7.2 BEARINGS
All bearings are supplied sealed for life and are, therefore, not
regreasable.
Important ! The life of a bearing in service is subject to
the working conditions and the
environment.
Important ! Long stationary periods in an environment
where there is vibration can cause false
brinnelling which puts flats on the ball and
grooves on the races. Very humid
atmospheres or wet conditions can emulsify
the grease and cause corrosion.
Important
! High axial vibration from the engine or
misalignment of the set will stress the
bearing.
The bearing, in service, is affected by a variety of factors that
together will determine the bearing life. We recommend that
the health of the bearings be monitored, using ‘spike energy’
vibration monitoring equipment. This will allow the timely
replacement of bearings, that exhibit a deteriorating trend,
during a major engine overhaul.
If excessive heat, noise or vibration is detected, change the
bearing as soon as practicable. Failure to do so could result in
bearing failure.
In the event that ‘spike energy’ vibration monitoring equipment
is not available, it is strongly recommend that consideration
be given to changing the bearing during each ‘major engine
overhaul’.
Belt driven application will impose an additional load on
bearings. The bearing life will therefore be significantly
affected. It is important that the side load limits given in
SECTION 3 are not exceeded and the health of the bearing is
monitored more closely.
7.3 AIR FILTERS
The frequency of filter maintenance will depend upon the
severity of the site conditions. Regular inspection of the
elements will be required to establish when cleaning is
necessary.
7.3.1 CLEANING PROCEDURE
Removal of filter elements enables access
to LIVE parts. Only remove elements with
the generator out of service.
Remove the filter elements from the filter frames. Immerse or
flush the element with a suitable detergent until the element is
clean. Dry elements thoroughly before refitting.
7.4 FAULT FINDING
Important
! Before commencing any fault finding
procedure examine all wiring for broken or
loose connections.
Four types of excitation control system, involving four types of
AVR, can be fitted to the range of generators covered by this
manual. The systems can be identified by a combination of
AVR type, where applicable, and the last digit of the generator
frame size designation. Refer to the generator nameplate then
proceed to the appropriate subsection as indicated below :-
DIGIT EXCITATION CONTROL SUBSECTION
6 SX460 AVR 7.4.1
4 AS440 AVR 7.4.2
4 7.4.3
5 Transformer control 7.4.4
3 MX341 AVR 7.4.5
3 MX321 AVR 7.4.6
7.4.1 SX460 AVR - FAULT FINDING
No voltage
build-up when
starting set
1. Check speed
2. Check residual voltage. Refer to
subsection 7.4.7.
3. Follow Separate Excitation Test
Procedure to check generator and
AVR.
Unstable voltage
either on no-load
or with load
1. Check speed stability.
2. Check stability setting. Refer to
subsection 4.6.
High voltage
either on no-load
or with load
1. Check speed.
2. Check that generator load is not
capacitive (leading power factor).
Low voltage
no-load
1. Check speed.
2. Check link 1-2 or external hand
trimmer leads for continuity.
Low voltage
on-load
1. Check speed.
2. Check UFRO setting. Refer to
subsection 4.7.1.1.
3. Follow Separate Excitation
Procedure to check generator and
AVR. Refer to subsection 7.5.
Danger !