SECTION FOUR
SERVICE AND MAINTENANCE
MAINTENANCE
Routine servicing of the a.c. generator is confined to an insulation resistance check on the windings if the machine has
not been run for a considerable length of time.
Insulation Test
Prior to testing the insulation to earth of the various windings, it is advisable that the A.V.R. is isolated from the
windings by disconnecting the push-on terminals. The machine can then be "Meggered" without risk of damaging the
control circuits.
FAULT FINDING PROCEDURE
Fault finding can be simplified considerably, by dividing the machine into two test sections:
A.
THE WINDINGS AND THE MAIN RECTIFIER ASSEMBLY
B.
THE ELECTRONIC CONTROL SYSTEM AND ITS WIRING
SECTION A THE WINDINGS AND THE MAIN RECTIFIER ASSEMBLY
Separately Exciting the Machine
The a.c. generator is separately excited to give an indication of the condition of the windings and main rectifier
assembly. For the frame sizes covered in this manual a 12 volt d.c. battery supply is sufficient to obtain the full output
voltage within + or - 10%, at no load, with the speed correct at nominal.
Fig. 2. Method of Separately Exciting the Machine
The d.c. supply is connected to the exciter stator leads marked X and XX , which should be removed from the A.V.R.
terminals X and XX respectively. It is also advisable to remove the rest of the push-on terminals from the A,V. R.
prior to this test.
With the battery connected to the stator leads, the machine is now run up to full speed (it Is essential that the speed is
correct for this test), and with a multimeter or voltmeter the following tests are made on the output from" the main stator
terminals.
Voltage is Balanced and within 10% of the Nominal
This indicates that the exciter windings, main windings and main rectifier diodes are In good working order. an: it is
therefore not necessary to carry out the following tests up to and including "Main Excitation Windings". Fault; finding
should continue with test "A.V.R. Sensing Supply from the Main Stator".
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