Operate generator

TM 9- 2920- 224- 34&P

OPERATIONAL TESTING OF THE GENERATOR - CONTINUED

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NOTE

If at any time during these tests it is discovered that

sparking is in excess of conditions described, disconnect

generator from test stand and connect it for additional

run--in operations. Perform run--in operations for an

additional two to three hours to properly seat all brushes.

4) Operate generator (with voltage regulator connected) at 6500 rpm, 30 volts, and 300 amperes until frame

temperature shows no more than 2 F temperature rise in five minutes. Measure and record voltage

between field terminal "D" and main (negative) terminal "E". Also record condition of commutation and

total field current. Commutations should not exceed "pin--point" sparking with pin--points along trailing

edges of brushes only. Paralleling voltage (between terminals "D" and ME) must be between 1.2 and 1.4

volts dc, provided air inlet temperature is approximately 80 F. Higher or lower temperatures will affect

paralleling voltages.

5) Operate generator at 6500 rpm, 30 volts, and check for compounding at 0 (zero) amperes, 150 amperes,

and 300 amperes. Record field current and condition of commutation. If generator is properly

compounded, shunt field current (at terminal "A") will not exceed 3.0 amperes and field current will

increase with an increase in load. Conversely, field current will decrease with a decrease in load.

Commutation (sparking) must not exceed pin--points along trailing edge of brushes.

6) Reduce generator speed slightly below 1850 rpm, but not below 1600 rpm. Substitute a 1.25 ohm resistor

for voltage regulator in field circuit and stabilize generator output at 26 volts, 250 amperes until frame

temperature shows no more than a 2 F temperature rise in five minutes. Adjust generator speed to hold

voltage and current constant at these values. Record field current, speed, frame temperature, and

condition of commutation. The "come--in" speed of generator must not exceed 1850 rpm. Come--in should

occur at between 1600 and 1800 rpm, at 250 amperes.

7) Remove generator from test stand and blowout all dust from commutator area with compressed air.

CAUTION

Do not attempt any insulation strength test of tube axial

fan on generator (10889713). Damage to tube axial fan

would result.

8) Connect 250 volts, 60 cycle AC, for one minute between a ground on generator housing and terminals

"A", "B", and "D" in succession. This is for determining strength of insulation in generator field coil. There

must be no indication of breakdown during the test. If a breakdown should occur, which would be

indicated by smoke or arcing inside generator, defective components must be replaced. If replacements

are required, perform the entire test procedure after assembly.

9) Connect cooling--air tube axial fan motor to a 24--28 V dc power source, with an ammeter connected in

series with input supply.

10) Allow tube axial fan motor to run until warm and take an ammeter reading. The amperage draw should

not exceed 11.5 amperes at any time. If in excess of this value, it indicates a mechanical drag on motor

armature, fan impeller, or an electrical defect. Remove motor from test circuit and check for trouble.

Make necessary corrections and recheck as outlined in above instructions.

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