Figure 3-1. Connections
for testing a.c.
or d.c. rotating machines.
3-7. Insulation Test of Ac
and Dc Rotating
b. Connect another test lead from the GROUND
Machines Rated Over 800 Volts
terminal to the shaft or frame of the equipment
a. Connect the equipment and test as directed
under test. Be sure that the surface to which the
for machines at 600 volts or less (para 3-6 above).
connection is made is free of paint or any other
b. Turn the hand generator crank
substance that is a nonconductor.
speed. If the machine is cold, readings should
c. Turn the hand generator crank
range between 10 and 100 megohms. Readings will
speed. If the machine is cold, the indication should
be lower if the equipment is warm.
be between 1 and 10 megohms. If the machine is
c. Direct current (dc) fields on ac machines
warm, the indication will be lower. Also, a large
should indicate between 1 and 10 megohms.
than a small machine.
3-8. Insulation Test
d. If all the circuits in the machine are not
a. Connect a test lead from the GROUND
interconnected as in separately excited generators,
terminal of the ohmmeter to the core or case of the
measure each circuit individually.