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Rev.12/31/97
commutation at full load will permit. Then the strength of the diverter-pole
winding should be adjusted to produce the flattest possible curve without
showing a rising voltage characteristic. Each point on the voltage curve
should be slightly lower as load is added. If the voltage rises at any point,
operation with a battery will be unstable.
winding should be adjusted to produce the flattest possible curve without
showing a rising voltage characteristic. Each point on the voltage curve
should be slightly lower as load is added. If the voltage rises at any point,
operation with a battery will be unstable.
The strength of the diverter-pole coils is adjustable by means of an
adjustable shunt connected in parallel with the diverter-pole circuit. This
shunt consists of resistance wire wound on an insulating tube and is usually
mounted inside one of the arms of the commutator end bearing bracket.
Clamp-type sliders provide means for adjusting the resistance of this circuit.
adjustable shunt connected in parallel with the diverter-pole circuit. This
shunt consists of resistance wire wound on an insulating tube and is usually
mounted inside one of the arms of the commutator end bearing bracket.
Clamp-type sliders provide means for adjusting the resistance of this circuit.
If commutation is not perfect, as evidenced by burning of the commutator
bars, shift brushes slightly in the direction of rotation. Moving the brushes
too far will make the generator slow to recover voltage following an overload.
Under this condition, the battery will regain voltage faster than the
bars, shift brushes slightly in the direction of rotation. Moving the brushes
too far will make the generator slow to recover voltage following an overload.
Under this condition, the battery will regain voltage faster than the
generator, which will result in a momentary discharge from the battery
through the generator. This condition will cause any reverse-current device
between the generator and the battery to trip open. When no reverse-
current device is used, this same condition may cause surging of current
between the generator and the battery to trip open. When no reverse-
current device is used, this same condition may cause surging of current
back and forth between the battery and the generator
C. Checking Voltage Regulation
C. Checking Voltage Regulation
When checking generator voltage regulation, always start the generator
without load and with the field rheostat resistance all cut in. Raise the
voltage slowly to the floating value, using care not to go beyond this value. If
this value is exceeded, shut down the generator, allow it to come to a
complete stop, and then start over. This procedure is important to eliminate
the effect of hysteresis.
without load and with the field rheostat resistance all cut in. Raise the
voltage slowly to the floating value, using care not to go beyond this value. If
this value is exceeded, shut down the generator, allow it to come to a
complete stop, and then start over. This procedure is important to eliminate
the effect of hysteresis.
Use a variable-resistance and increase the load in successive steps to a point
where the generator voltage drops sharply, recording the generator volts and
amperes on each step.
Be sure that each successive step increases the load to eliminate the effect
of hysteresis.
The generator should always be run long enough to produce a perfect and
full seating of the brushes on the commutator before taking final check test
readings.
where the generator voltage drops sharply, recording the generator volts and
amperes on each step.
Be sure that each successive step increases the load to eliminate the effect
of hysteresis.
The generator should always be run long enough to produce a perfect and
full seating of the brushes on the commutator before taking final check test
readings.
The final voltage curve should show a drop as the first small increments of
load are added in order to prevent a swing to discharge on light loads. The
load should then level off to a very gradual drop over the major portion of
the curve to ensure stability until cutoff point is reached, then the load
should drop abruptly to protect the generator against overloads beyond its
safe capacity.
load are added in order to prevent a swing to discharge on light loads. The
load should then level off to a very gradual drop over the major portion of
the curve to ensure stability until cutoff point is reached, then the load
should drop abruptly to protect the generator against overloads beyond its
safe capacity.
D. Motor-Generator Bearing Maintenance
D. Motor-Generator Bearing Maintenance