(17) Using a double bridge, measure resis-
(28) After rewinding, vacuum impregnate the
tance of rotor core. Resistance shall be 0.2154 to
stator assembly as follows:
0.2486 ohms at 77F (25C).
(a) Place wound stator in an oven at 300
(18) Install rotor and balance assembly on a
F (-0, +15 F (149 C) for 120 10 minutes.
dymetric balance machine and check for static and
dynamic balance. Unbalance shall not exceed 0.5
(b) Transfer stator to vacuum tank.
inch-ounce in either balance plane. Balance rotor
and balance assembly as outlined in step (25) below.
(19) Install blower and coupling disc assem-
bly on a dymetric balance machine and check both
Do not allow temperature of stator to
static and dynamic balance. Unbalance shall not
drop below 125 F.
exceed 0. 5 inch-ounce in either plane. Balance blow-
er and coupling disc assembly aa outlined in step (26)
(c) Evacuate tank to a maximum of 50 mm
Hg absolute and hold for 10 minutes (minimum).
(20) Use a double bridge to measure resis-
(d) Without breaking the vacuum, intro-
each phase shall be O. 1473 to O. 1627 ohm at 770 F
(25C). Difference between phase reading shall not
Type M, Class 155) to a sufficient depth to complete-
exceed 2 percent.
ly cover the stator. Hold vacuum for 5 minutes (mini-
by applying 300 Vac at 60 Hz RMS for 1 second be-
(e) Break vacuum and hold at atmospheric
tween one terminal and ground (frame). There shall
pressure for 5 minutes (minimum).
be no evidence of dielectric breakdown.
(f) Return varnish to storage tank and
(22) Using a double bridge, measure resis-
allow the stator to drain.
tance between terminals of exciter stator. Resis-
tance shall be 4.50 to 5.50 ohms at 77F (25C).
(g) Place the impregnated stator in an
oven at 300 F, -O F, +15F, (149C) for 120 10
(23) Using 374 megger tester, ground test
stator assembly by applying 750 Vac at 60 Hz RMS
(29) If damage to rotor core windings is dis-
for one second between all leads (tied together)
covered at inspection and test, rewind in accordance
and the frame. Apply 500 Vac at 60 Hz RMS for one
second between phases with neutral open. There
shall be no indication of dielectric breakdown in
(30) Impregnate the wound rotor as follows:
(a) Mark all fit surfaces to prevent the
(24) Use semiconductor test set to test recti-
resin from adhering.
fiers for inverse current leakage at peak recurrent
voltage of 600 volts leakage shall not exceed 20.0
(b) Preheat the wound core for 2 hours
milliamperes at 77F (25 C). Check forward voltage
(minimum) at 302F (150C) (minimum).
drop. Voltage drop shall not exceed 1.2 volts at
(c) Allow the core to cool in ambient
(25) If rotor and balance assembly is out of
surroundings to 104F (40C) (maximum).
balance, add or subtract balance weights until re-
maining unbalance in both balance planes does not
(d) Place the core in the vacuum tank and
evacuate to 1 to 5 mm Hg and hold for 15 minutes.
exceed 0. 5 ounce-inch Once rotor and balance as-
sembly is balanced, each weld balance weights and
(e) Without breaking the vacuum, admit
the resin into the tank to a sufficient depth to cover
(26) If blower and coupling disc assembly is
the core. Hold the vacuum for a minimum of 5 min-
out of balance, correct by machining material from
inner diameter of blower as required. Remaining
unbalance shall not exceed 0.5 inch-ounce in both
(f) Break the vacuum and pressurize the
tank to 85 to 90 psig. Hold for a minimum of 30 min-
(27) If damage to the stator windings is dis-
covered during inspection and test, rewind using
(g) Reduce the pressure to zero, then in-
crease as necessary to remove the resin from the tank.