3. Set the AVR VOLTS control potentiometer fully
clockwise.
4. Connect a 12V, 1.0A DC supply to the exciter field leads
X & XX (F1 & F2) with X (F1) to the positive.
5. Start the generating set and run at rated speed.
6. Check that the generator output voltage is within +/-10%
of rated voltage.
Voltages at AVR terminals 7-8 on SX460 AVR or P2-P3 on
SX440 or SX421 AVR should be between 170 and 250 volts.
If the generator output voltage is correct but the voltage on 7-
8 (or P2- P3) is low, check auxiliary leads and connections to
main terminals.
Voltages at P2, P3, P4 terminals on MX341 and MX321 hould
be as given in 7.5.1.
The lamp connected across X-XX should glow. In the case of
the SX460, SX440 and SX421 AVRs the lam p should glow
continuously. In the case of the MX341 and MX321 AVRs the
lamp should glow for approximately 8 secs. and then turn off.
Failure to turn off indicates faulty protection circuit and the
AVR should be replaced. Turning the "VOLTS" control
potentiometer fully anti-clockwise should turn off the lamp with
all AVR types.
Should the lamp fail to light the AVR is faulty and should be
replaced.
Important ! After this test turn VOLTS control
potentiometer fully anti-clockwise.
The transformer rectifier unit can only be checked by
continuity, resistance checks and insulation resistance
measurement.
Separate primary leads T1-T2-T3-T4 and secondary leads 10-
11. Examine windings for damage. Measure resistances
across T1-T3 and T2-T4. These will be a lo w valu e but should
be balanced. Check that there is resistance in the order of 8
ohms between leads 10 and 11. Check insulation resistance
of each winding section to earth and t o other winding
sections.
Low insulation resistance, unbalanced primary resistance,
open or short circuited winding sections, indicates the
transformer unit should be replaced.
Separate primary leads T1-T2-T3 and secondary leads 6-7-8
and 10-11-12.
Examine windings for damage. Measure resistances across
T1-T2, T2-T3, T3-T1. These will be low but should be
balanced.
Check that resistances are balanced across 6-10, 7-11 and
8-12 and in the order of 18 ohms. Check insulation resistance
of each winding section to earth and t o other winding
sections.
Low insulation resistance, unbalanced primary or secondary
winding resistances, open or short circuited winding sections
indicates the transformer unit should be replaced.
With the leads 10-11-12-X and XX removed from the rectifier
unit (lead 12 is not fitted on single phase transformer rectifier
units), check forward and reverse resistances between
terminals 10-X, 11-X, 12-X, 10-XX, 11-XX and 12-XX with a
multimeter.
A low forward resistance and high reverse resistance should
be read between each pair of terminals. If this is not the case
the unit is faulty and should be replaced.
7.5.3 REMOVAL AND REPLACEMENT OF COMPONENT ASSEMBLIES METRIC THREADS ARE USED THROUGHOUT
When lifting single bearing generators,
care is needed to ensure the generator
frame is kept in the horizontal plane. Th e
rotor is free to move in the frame and can
slide out if not correctly lifted. Incorrect
lifting can cause serious personal injury.
1. Remove 4 screws holding the sheet metal cylindrical
cover at the non-drive end and remove the cover.
2. Disconnect the in line connector from the PMG stator (3
wires go to this connector). It may be necessary to cut off
the nylon cable tie first.
3. Remove the 4 threaded pillars and clamps holding the
PMG stator onto the end bracket.
4. Tap the stator out of the 4 spigots and withdraw. The
highly magnetic rotor will attract the stator. Take care to
avoid contact which may damage the windings.
5. Remove the bolt in the centre from the rotor shaft and
pull off the rotor. It may be necessary to gently tap the
rotor away. Take care to tap gently and evenly - the rotor
has ceramicmagnets which are easily broken by shock.
Important ! The rotor assembly must not be dismantled.
Replacement is a reversal of the above procedure.
7.5.3.2 REMOVAL OF BEARINGS Important ! Position the main rotor so that a full pole
face of the main rotor core is at the bottom
of the stator bore.
NOTE: Removal of the bearings may be effected either after
the rotor assembly has been removed OR more simply by
removal of endbracket(s). Refer to 7.5.3.3. and 7.5.3.4.
The bearings are pre-packed with grease and sealed for life.
Caution !