Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to dynamoelectric machines
and, in particular, to direct cooled dynamoelectric machines
of the type including a rotating field comprising electrically
conductive windings disposed in a plurality of axially extend-
ing slots.
The rotating field of a dynamoelectric machine
includes a rotor body having a plurality of axially extending
slots into which the electrical windings are inserted. The
rotor body is generally a steel material whereas the rotor
windings comprise a plurality of copper wires. In a direct
cooled dynamoelectric machine each slot may further include
an axially extending sub-slot for ventilation and cooling.
The direct cooled machine is one which is cooled directly
by the atmosphere in which it is disposed; e.g., air or
hydrogen. The sub-slots are part of a ventilation scheme,
known in the art, for transferring gas coolant axially along
the rotor. Each slot also includes provisions for the radial
flow of gas coolant primarily through ventilation slots
in the windings.
In the afore-described machine it is necessary
to electrically insulate the rotor windings from the rotor
body such insulation taking the form of non-conductive
"slot armor". Moreover, it has been the practice
of some manufacturers to provide sub-slot covers which increase
the insulation of the bottom of the slot. In a direct
cooled dynamoelectric machine wherein the machine coolant
is air it is possible that foreign material may accumulate
on sub-slot surfaces in such a way as to reduce electrical
creepage distances and lead to low insulation resistance or
a grounded field.
It is one object of the present invention to
provide an improved sub-slot cover for a dynamoelectric
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machine rotating field.
It is another object of the present invention
to provide an improved sub-slot cover for a dynamoelectric
machine field which increases the electrical creepage
distances between the field windings and the rotor.
It is still another object of the present inven-
tion to provide an improved sub-slot cover for a direct
cooled dynamoelectric machine field which reduces the
possibility of inadvertent grounding of the field windings
which may be caused by the accumulation of foreign deposits.
~he novel features believed characteristic of the
present invention are set forth in the appended claims.
The invention itself, however, together with further
objects and advantages thereof, may best be understood with
reference to the following description taken in connection
with the appended drawings.
In accordance with the foregoing objects of the
invention a sub-slot cover is formed to be inserted along
the axial length of a winding slot. The sub-slot cover is
inserted into the slot and the coils are thereafter laid
onto the sub-slot cover. One unique feature, of the sub-
slot cover construction is a pair of oppositely directed
grooves or slots formed on each side of the sub-slot cover
and into which one end of the slot armor is inserted.
Interlocking of the slot armor and sub-slot cover extends
the length of the electrical creepage path.
A second feature in accordance with one embodiment
of the invention is provided by a pair of fins which extend
radially inwardly into the sub-slot to interrupt the ~enerally
flat configuration of the sub-slot cover thereby increasing
once again the electrical creepage path by obviating the
accumulation of foreign material on the underside of the
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sub-slot cover.
Figure 1 is an end view of a generator rotor and
stator showing in cross-scetion the electrical field and
armature windings.
Figure 2 is a prior art showing of a rotor slot
and sub-slot including several strands of field windings.
Figure 3 is a cross-section view similar to
Figure 2 updating the prior art with one embodiment of the
applicant's invention.
Figure 4 is a perspective view of a new sub-slot
cover according to the applicant's invention.
Figure 1 shows an end view schematic partially in
cross-section of a dynamoelectric machine 11 which includes
a frame mounted stationary armature core or stator 13
comprising a plurality of stacked laminations having
axially directed electrically conductive armature bars
17 running the length of the machine and terminating in
end windings at each of the dynamoelectric machine. The
reader will note that only a portion of this well known
construction has been shown, the exact details of which are
generally available and not particularly germane to the
present invention except by way of explanation. The
radially inner dovetail slots 19 and the radially outer
dovetail slots 21 accommodate stator wedges and keybars
respectively (not shown) which maintain the alignment
and spacing of stator core laminations. The stator bars
carry induced current to the dynamoelectric machine terminals.
A rotor 25 is positioned co-axially within the
stator core and includes a cylindrical steel rotor body in
which there are a pluarlity of field windings 27. The
field windings are electrically conductive members; e.g.,
copper, which carry excitation current into the dynamoelectric
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machine. The rotor is rotatably supported at each end of
the dynamoelectric machine on bearings well known in the
art. The field windings are held in place against centrifu-
gal forces by dovetail wedges 31.
Referring to Figures 2 and 3, the prior art and
the applicant's invention are shown relative to a single
rotor winding in that respective order. The drawings show
a portion of the rotor steel 41 which has a channel
shaped slot 43 formed therein to accept the rotor field
windings 27. The windings are current carrying copper wires
which must be electrically insulated from the rotor steel.
This is accomplished by so called slot insulation
including slot armor 45, a channel shaped piece of glass
laminate having spaced ventilation slots 47 along the axial
length of the piece. The ventilation slots 47 are in
register with radial openings 49 up through the field
wlndlngs.
In a direct cooled machine, the field windings
are cooled by the surrounding gaseous atmosphere by being
pumped radially through the windings and axially through
the rotor sub-slots 51. The slot insulation is further
enhanced by a sub-slot cover 53 which is interposed between
the sub-slot and the slot armor.
In order to understand the advantages of the
present invention we must look into the disadvantages of
the prior art. The problem involves current leakage
paths which might lead to a grounded field. These paths
are indicated by the arrows A and B superposed on
Figure 2. Arrow A indicates a leakage path between the
slot armor 45 and the sub-slot cover 53. Arrow B indicates
a leakage path on the radially inner surface of the sub-
slot cover, this latter path being a low resistance path
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generated by the deposit of minute particles of foreign
matter being thrown in the radially outward direction by
centrifugal force. The minute particles are carried into
the machine from the surrounding environment by the coolant
gas.
The present invention is shown in a preferred
embodiment in Figure 4O The sub-slot cover according to
the present invention is a substantial]y planar member
which includes an upper (radially outer) surface 61 and
a lower (radially inner) surface 63. Between the two
surfaces, there are two oppositely directed grooves or
slots 65 which are made to interlock with the slot armor.
The slots extend along the axial length of the sub-slot
cover. Returning to Figure 3, the effect of this construction
is to obviate leakage path A demonstrated in Figure 2.
Again, it is the interlock between the grooves in the
sub-slot cover and the base legs of the slot armor which
forms a part of this invention.
Continuing with the detailed description of the
present invention, the lower or radially inner surface
of the sub-slot cover is formed with a pair of radially
inwardly extending fins 67 which also extend along the axial
length of the sub-slot cover. The fins extend radially
inwardly into the sub-slot. It will be understood of course
that the broad aspects of the inventive concept include
embodiments having at least one radially inwardly extending member
or fin. The function of the fin is obviously to extend the
leakage path based upon that leakage path B indicated in Figure 2.
It is a further, but less apparent function of the fins to
provide walls to which minute particles cannot cling as
they are flung in the radially outward direction
by centrifugal force and hence, the walls become
barriers to electrical leakage vis-a-vis path B.
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The improved sub-slot cover is also formed with a ventilation
slot 69 and may be made of any suitable insulating material
such as glass laminate.
While there has been shown what is considered
to be a preferred embodiment of the present invention
other modifications may occur to thos having skill in the
art. It is intended to cover in the appended claims
all such modifications which fall within the true spirit
and scope of the claims.
