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Main Field (Rotor)
1. Disconnect the generator field leads from the posi tive and
negative terminals of the rotating rectifier assembly.
2. Connect 500 V megger: one clamp to the positive and negative
generator field leads, the second clamp of the megger to the
shaft.
3. Apply 500 V from the megger. After 1 minute, measure the
resistance reading. The reading must be a minimum of 50
megohms. If it is not, refer to the cleaning or dry out procedures.
4. Disconnect the megger and wait a minimum of 1 minute. Ground
the generator field leads to the shaft to discharge the residual
voltage.
Main Armature (Stator) — individual phases
1. Separate the neutral connection point (if not possible, test all
phases simultaneously per instructions below).
2. Disconnect power connections and all control apparatus from the
generator terminals.
3. Test each phase starting with phase A.
4. Ground phase B and phase C leads to the frame.
5. Connect the megger to test phase A: one clamp to the phase A
leads, the second clamp to the frame.
6. Apply voltage per Table 2 based on the winding rated voltage.
After 1 minute observe the resistance reading. The reading must
be a minimum of 50 megohms. If it is not, refer to the cleaning
or dry out procedures.
7. Disconnect the megger and wait a minimum of 1 minute. Ground
the leads to the frame to discharge the residual voltage.
8. Repeat procedure for phase B (with phase A and C grounded)
and phase C (with phase A and phase B grounded).
Main Armature (Stator) — all phases simultaneously
1. Disconnect power connections and all control apparatus from the
generator terminals.
2. Connect the megger: one clamp to the main armature leads, the
other clamp to the frame.
3. Apply voltage per Table 2 based on the winding rated voltage.
After 1 minute observe the resistance reading. The reading must
be a minimum of 50 megohms. If it is not, refer to the cleaning
or dry out procedures.
4. Disconnect the megger and wait a minimum of 1 minute. Ground
the leads to the frame to discharge the residual voltage.
Dry Out Procedures
If the insulation resistance readings are below the recommended
minimum values specified previously, use one of the dry out
procedures described below. Select the procedure based on the size
and location of the unit, available equipment, and experience of
personnel. Before drying, remove the voltage regulator, and cover all
inlet and discharge openings.
Provide an opening at the top of the machine, preferably at the fan
end, for moisture to evaporate.
CAUTION:
Do not apply heat too
rapidly. It could damage the windings.
Table 2 Guide for DCV to be Applied
During Insulation Resistance Tests
Winding
Rated
Voltage (V)*
Insulation
Resistance Test
Direct Voltage (V)
<1000
500
1000–2500
500–1000
2501–5000
1000–2500
5001–12000
2500–5000
>12000
5000–10000
*
Rated line–line voltage for three-phase
AC machines, and line–ground voltage
for single-phase machines, and rated
direct voltage for DC machines or field
windings.
Summary of Contents for 4P10
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