Figure 8-16 shows a wave type of coil. Figure 8-17 gives a 6-pole wave winding. Study reveals that it has only two parallel paths between the positive and negative terminals. Thus, only two sets of brushes are needed
Each brush shorts p/2 coils in series. Because points a, b,
and c are at the same potential (and, also, points d, e, and f ), brushes can
be placed at each of these points to allow a commutator one-third as long.
The winding must progress or retrogress by one commutator
bar each time it passes around the armature for it to be singly reentrant.
Thus, the number of bars must equal (kp/2) # 1, where k is a whole number and p
is the number of poles. The winding needs no equalizers because all conductors
pass under all poles.
Although most wave windings are 2-circuit, they can be
multicircuit, as 4 or 16 circuits on a 4-pole machine or 6, 12, or 24 circuits
on a 12-pole machine. Multicircuit wave windings with the same number of
circuits as poles can be made by using the same slot and bar combinations as on
a lap winding.
For example, with an 8-pole machine with 100 slots and 200
commutator bars, the bar throw for a simplex lap winding would be from bar 1 to
bar 2 and then from bar 2 to bar 3, etc. For an 8-circuit wave winding, the
winding must fail to close by circuits/2 bars, or 4. Thus, the throw would be
bar 1 to 50, to bar 99, to bar 148, etc.
The throw is (bars # circuits/2)(p/2), in this case, (200 #
4)/4 # 49. Theoretically such windings require no equalizers, but better
results are obtained if they are used. Since both lap and multiple wave
windings can be wound in the same slot and bar combination simultaneously, this
is done by making each winding of half-size conductors.
This combination resembles a frog’s leg and is called by
that name. It needs no equalizers but requires more insulation space in the
slots and is seldom used.
Some wave windings require dead coils. For instance, a large
10-pole machine may have a circle of rotor punchings made of five segments to
avoid variation in reluctance as the rotor passes under the five pairs of
poles.
To avoid dissimilar slot arrangements in the segments, the
total number of slots must be divisible by the number of segments, or 5 in this
case. This requires the number of commutator bars to be also a multiple k of 5.
However, the bar throw for a simplex wave winding must be an
integer and equal to (bars # 1)(p/2). Obviously (5k # 1)/5 cannot meet this
requirement.
No comments:
Post a Comment