Figure 7-64.--Three-phase, four-pole, parallel-delta winding.
motor are (1) changing the direction of current flow
through the armature leads and (2) changing the
direction of current flow through the motor fields. In
compound motors the reversing of rotation is easier
using the first method since a single element is involved.
If the second method is used, it becomes necessary to
reverse the current through both the series field and
shunt field windings.
REVERSING DIRECTION OF ROTATION OF
A THREE-PHASE MOTOR.-- To reverse the
direction of rotation of a three-phase motor, all that
needs to be done is to reverse the connections of any two
of the three leads of the motor. That is, reverse either
the A and B, A and C, or B and C phase leads.
Checking Motor and Generator Speeds
Tachometers indicate, in revolutions per minute
(rpm), the turning speed of motors, generators, and other
rotating machines. With the unit operating under
Figure 7-65--A chronometric tachometer.
normal conditions, use a portable tachometer (fig. 7-65),
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