Bearing Withdraw; Maintenance Of The Exciter; Exciter; Test On The Diodes - WEG G Serie Manual De Instalación, Operación Y Mantenimiento

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6.5.2.3 Bearing withdraw

Bearing withdraw should always be made with the use of
appropriate tools (bearing puller).
Figure 6.1: Device to withdraw bearings
ATTENTION
A bearing should only be removed from the
shaft when absolutely necessary
Instructions:
1. The extractor grabs must be applied on the side of the
bearing inner ring to be disassembled or on an
adjacent part.
2. Before installation of new bearings, the shaft seats
should be cleaned and lightly lubricated.
3. The bearings must be heated to a temperature
between 50 °C and 100 °C to facilitate assembly.
4. The bearings should not be subjected to shock, drops,
storage with vibration or humidity, which can cause
marks on the internal races or in the balls, reducing
their life.

6.6 MAINTENANCE OF THE EXCITER

6.6.1

Exciter

For the proper performance of its components, the exciter
alternator should be kept clean.
Check the insulation resistance of the windings of the
exciter main and of the auxiliary exciter (if any) periodically
to determine the insulation condition of the same by
following the procedures described herein.
6.6.2

Test on the diodes

Diodes are components that have great durability and do
not require frequent tests. If the alternator indicating a
defect presents failure in the diode or an increase in field
current for the same load condition, then the diodes
should be tested in accordance with the following
procedure:
1. Release the connections of all the diodes with the rotor
winding of the exciter;
2. With an ohmmeter, measure the resistance of each
diode in both directions.
NOTE
When testing diodes, observe the polarity of
the test terminals in regard to polarity of the
diode.
The polarity of the diode is indicated by an
arrow on its frame.
40 l Installation, operation and maintenance manual – Synchronous Alternator – G line - Horizontal
The current conduction must occur
only in the anode-cathode direction,
i.e. in the condition of direct
polarization.
The diode is considered good when presenting low
ohmic resistance (up to approximately 100 Ω) in its
forward direction and high resistance (approx. 1 MΩ) in
opposite direction. Defective diodes have ohmic
resistance 0 Ω or greater than 1 MΩ action in both
measured directions.
In most cases, the method with ohmmeter to test the
diodes is sufficient to identify faults in the diodes.
However, in some extreme cases it may be necessary to
apply the rated voltage of blocking and / or current flow
for detecting fault in the diodes. Due to the efforts required
for these tests, in case of doubt, it is recommended to
perform the exchange of the diodes.
6.6.3

Diodes replacement

To access the diodes and perform the exchange, it is
necessary to:
Disassemble the alternator (frame 160);

Remove the back inspection cover (frame 200);

Remove the back multi-leaf damper (frames 250 to 400);

For other frames, refer to WEG.

To replace the diodes, proceed as follows:
Undo the connection of the 6 diodes to the exciter rotor;

Release support for diodes of the exciter rotor and

remove it;
Secure the support in a bench lathe with protection on

the jaw, and remove all diodes;
Install three new diodes of the same polarity (AND or

CTD) in one of two connection bridges;
Install the other connecting bridge, three new diodes of

polarity opposite of the three diodes previously installed;
Secure all diodes, tightening them with a torque wrench

respecting the tightening torques in Table 6.2;
Secure the set of diodes in the exciter rotor;

Make the connections of the diodes with the exciter

rotor winding.
ATTENTION
It is essential that the indicated tightening
torques are respected so that the diodes are
not damaged in the assembly.
Table 6.2: Tightening torque of the diodes
Diode base Torque key of
thread (mm) torque meter (mm)
M6
M8
M12
M16
Tightening
torque (Nm)
11 2
17 4
24 10
32 30
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