Insulation Test of Insulating Bushings

TM 11-6625-298-14

CAUTION

NOTE

Do not exceed the voltage rating of the

The ohmmeter pointer will dip toward zero

capacitor under test.

when the crank is first turned, but will

a. Connect a test lead from the GROUND

move up the scale as the capacitor becomes

terminal of the ohmmeter to the case of the

charged with the test potential. The

capacitor must be fully charged with the

b. Connect another lead from the LINE terminal

test potential before a reading may be

of the ohmmeter to one of the terminals of the

taken. To be sure that the capacitor is fully

capacitor.

charged, turn the generator crank for one

c. Turn the hand generator at operating speed.

minute.

The indication obtained is the insulation between

e. Turn the crank handle at operating speed. The

insulation reading should be 500 megohms or

the capacitor and its case. The indication should be

500 megohms or more.

greater.

d. Remove the GROUND lead from the case of

the capacitor and connect it to the remaining

terminal of the capacitor.

Figure 3-3. Connections for testing capacitors.

speed. If the bushing under test is the dry type,

3-10. Insulation Test of Insulating Bushings

the reading should be INFINITY or near IN-

a. Connect a test lead from the GROUND

FINITY. If the bushing under test is the filled

terminal of the ohmmeter to the base of the

type, the reading should be near 1,000 megohms.

bushing.

d. If the reading is lower than near INFINITY

b. Connect another test lead from the LINE

for a dry-type bushing or 1,000 megohms for a

terminal of the ohmmeter to the bushing terminal.

filled-type bushing, connect the third test lead to

c. Turn the hand generator crank at operating