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Vertical Drilling Motor, Type GE752, GEK–91584D
13
Insulation
Measure the insulation resistance with a meg– ohm-
meter (Megger) to determine the condition of the insula-
tion. If reading is low, make a further inspection to deter-
mine if insulation failure or excessive moisture is caus-
ing the low megohmmeter reading. Correct the cause of
low readings before returning the motor to service.
Inspect all accessible parts of the field coil insulation
for cracking and evidence of overheating.
Power Cables
Inspect the power cables for signs of excessive heat-
ing, poor insulation or mechanical damage. Assure all
terminals are tight. Replace any cables which show low
insulation resistance or will not stand 75% above rated
voltage.
Mounting Bolts
Check all mounting bolts to assure tightness.
SEMI–ANNUALLY
1. Perform inspection operations listed under
Monthly section.
2. Refer to the DATA section for the Brushholder
Clearance dimension, and check the clearance
between the brushholders and the commutator
surface.
If clearance adjustment is required, refer to the BA-
SIC REPAIRS, Brushholder Clearance Adjustment sec-
tion for instructions.
BASIC REPAIRS
BRUSH REPLACEMENT
NOTE: Brush spring pressure is pre–set and
non–adjustable for the brushholders used on
these machines. Any brushholder that is dam-
aged or has a low spring pressure should be re-
placed before installing new brushes. Spring
pressure can be measured with a 20–lb. spring
scale pulling radially on the brush pressure fin-
ger over the center of each brush. See the DATA
section for limits.
1. Remove the commutator inspection covers.
2. Disconnect the brush shunt from the terminal
screw, Fig. 5, located on the brushholder body.
3. Lift the pressure finger away from the brush to
the toggled–up position. Remove the brush.
4. Use dry, compressed air and blow the carbon
dust from the carbonway.
WARNING: When using compressed air for clean-
ing purposes, flying debris and particles may
present a hazard to personnel in the immediate
area. Personnel should be provided with, and
trained in the use of, personal protective equip-
ment as specified by applicable federal or state
safety regulations.
5. Insert a new brush and make sure it slides freely
in the carbonway.
6. Carefully lower the pressure finger on the brush.
Do not allow the finger to snap down on the
brush; this could damage the brush.
7. Bolt the brush shunt terminals to the brushhol-
der(s). Arrange the brush shunt strands so they
clear the pressure fingers, Fig. 6, and tighten the
terminal screw(s). Make sure brush shunts are
not positioned under the pressure fingers. Check
and tighten all brushholder cable connections.
8. Seat the new brushes with a white seater stone.
CAUTION: When replacing brushes, use the GE
recommended grade. Mixing of brush grades in
the same motor or changing brushes to another
grade will seriously affect commutation, surface
film, commutator and brush life. See the DATA
section for brush grade.
BRUSHHOLDER REPLACEMENT
Removal
1. Remove brushes from the brushholders and
cover the commutator with heavy paper.
2. Disconnect the cable from the brushholder(s) in-
volved.