Salient pole rotor for a dynamoelectric machine

A dynamoelectric machine has a stator with a stator core and a plurality of spaced apart radially extending ventilation ducts. A rotor mounted for rotation within the stator has a shaft with a plurality of salient poles. Each salient pole has a winding on it and each pole with its winding constitutes a pole member. Adjacent pole members define between them an interpolar space. Cooling air enters each interpolar space from each end when the machine is operating, moves generally axially as portions of the air change direction to move radially outwards through the air gap separating the rotor and stator and then through the ventilation ducts. The air flow, in a radial outward direction, tends to be less at the ends of the rotor and through the ventilation ducts adjacent the ends of the stator. The invention places a baffle at each end of each interpolar space. The baffle is in a generally radial plane and has an outward edge adjacent the outer limit of the interpolar space as defined by the tips of the poles, and an inward edge spaced from the bottom of the interpolar space. The baffle improves the air flow radially outwards adjacent the ends of the rotor and the stator.

BACKGROUND OF THE INVENTION 
This invention relates to a salient pole rotor for a dynamoelectric 
machine, and in particular it relates to a rotor having a baffle 
arrangement to improve the air flow distribution. 
In a dynamoelectric machine having a rotor with salient poles, it is 
desirable to have not only the temperatures axially along the rotor as 
uniform or even as possible, but also to have the temperatures axially 
along the stator as even as possible. In a machine with no rotor fan, the 
circulation of the cooling gas (which will be referred to hereinafter as 
air) is pumped or driven by the rotating rotor across the air gap and 
through ventilation gaps or ducts in the stator core. The temperatures of 
the stator core, measured axially along the core, tend to be higher at the 
ends of the core. This is usually because the static pressure of the 
circulating air at the ducts adjacent the ends of the stator core tends to 
be lower. It is, of course, the higher temperatures that must limit the 
operation of the machine, and it is desirable that the higher temperatures 
be reduced. 
SUMMARY OF THE INVENTION 
The present invention provides a baffle arrangement which tends to increase 
the static pressure adjacent to the ends of a salient pole dynamoelectric 
machine, and consequently increase the flow of cooling air in the portions 
of the machine adjacent the ends. 
It is therefore an object of the invention to provide for a dynamoelectric 
machine, a salient pole rotor having a baffle arrangement for increasing 
the static pressure of the cooling air as it leaves the end portions of 
the rotor and enters cooling ducts adjacent to the ends of the stator. 
It is another object of the invention to provide a baffle for a salient 
pole rotor where the baffle extends in a substantially radial plane 
between adjacent pole members at the ends thereof and having a radially 
outward edge adjacent the periphery of the rotor and an inward edge spaced 
from the bases of the adjacent pole members. 
In accordance with one form of the invention there is provided a 
dynamoelectric machine having a salient pole rotor with an axially 
extending shaft mounted for rotation within a stator, the rotor having no 
ventilation fan associated therewith, the rotor and the stator defining 
therebetween an air gap, the stator having a stator core with stator 
windings thereon, the stator having a plurality of spaced apart, 
ventilation ducts extending radially from the air gap to an exhaust 
region, the dynamoelectric machine being cooled by a cooling gas 
circulated through the rotor and stator, the rotor comprising a plurality 
of axially extending, spaced apart poles, mounted on the shaft, each pole 
having a base where it mounts to the shaft and a pole tip radially 
outwards of the base and defining a periphery of rotation, a winding on 
each pole, each pole and respective winding thereon forming a pole member, 
adjacent pole members defining therebetween an interpolar space, at least 
one coil bracket in each interpolar space, each coil bracket having a 
central portion with extending arm portions, means for fastening each coil 
bracket to the shaft at the central portion thereof, the respective arm 
portions engaging the surface of the adjacent windings of adjacent pole 
members for aiding in securing the windings, a baffle at each end of each 
interpolar space, each of the baffles being in a substantially radial 
plane and extending between adjacent pole members with a radially outward 
edge adjacent the periphery of rotation and an inward edge spaced 
outwardly from the bases of the adjacent pole members, with rotation of 
the rotor the baffles tending to increase at each end of the rotor the 
static pressure of the cooling gas within the machine in the air gap 
adjacent the ends of the rotor thereby improving the flow of the cooling 
gas radially outwards through the air gap and the stator ventilation ducts 
adjacent the ends of the stator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown an isometric view of one end of a 
salient pole rotor 12 having a shaft 10 and a rim 11. Four salient poles 
14 are mounted to rim 11. Each pole 14 has a base 15 and a pole tip 16. 
Also, each pole has a winding 17, as shown. The turn portions or end 
portions of the winding 17 have been omitted for ease of drawing. Each 
pole 14 with its respective winding 17 forms a pole member 18. The region 
or space between adjacent pole members 18 may be referred to as an 
interpolar space 24, and in each interpolar space 24 there is at least one 
coil bracket 19. Each coil bracket 19 has a central portion 20 and 
extending arms 21 and 22 which extend in opposite directions. A bolt 23 
through the central portion 20 secures the coil bracket 19 to the rim 11. 
The arms 21 and 22 engage the surface of the respective windings 17 of the 
adjacent ones of pole members 18 to assist in holding the windings or 
coils in place against forces caused by rotation. As will be discussed 
hereinafter, there may be a plurality of spaced apart coil brackets 19 in 
each interpolar space 24 and the central portion 20 may have different 
thicknesses, that is, the outer surface of the central portions may be at 
different radial distances from the axis of rotation. 
At each end of rotor 12 in each interpolar space 24 there is a baffle 25 
which lies in a substantially radial plane. Baffle 25 is also shown, for 
example, in FIG. 3A. 
Referring for the moment to FIG. 3A, there is shown an end view of a rotor 
12, again with the ends of windings 17 omitted. The rotor 12, when 
rotating, defines with the pole tips 16 a periphery of rotation 26, 
indicated by a broken line. Each baffle 25 extends between adjacent ones 
of pole members 18 and has an outer edge 27 which is adjacent the 
periphery of rotation 26 and an inner edge 28 spaced outwardly of the 
bases 15 of the adjacent ones of pole members 18. Thus, the baffles 25 
extend across the radially outward portion of the end of each interpolar 
space 24 but do not extend across the inner portion. The outward edge 27 
of each baffle may be straight as shown in FIG. 3A or curved as shown in 
FIG. 3B. 
Referring for the moment to FIG. 3B, there is shown an end view of a rotor 
12, similar to that of FIG. 3A, but with a baffle 25A that has a different 
configuration. The baffle 25A has a straight inner edge 28, but has an 
outer edge 27A which is curved and generally follows the periphery of 
rotation 26. Thus, the outer edge of each baffle (in a radial direction) 
may be straight, curved or a combination of straight and curved. In each 
instance the outer edge of the baffles is adjacent the periphery of 
rotation. 
Referring to FIGS. 4A and 4B, there is shown in FIG. 4A a cross-sectional 
view of baffle 25, and there is shown in FIG. 4B a cross-sectional view of 
an alternate form of a baffle 25C. Baffle 25C has at least an inner edge 
28C that is curved on the outer surface in an axial direction inward to 
improve the air or gas flow into the interpolar spaces. The baffles 25C 
may be said to form a bell-mouth at the end of the rotor. The baffle 25C, 
as shown, has both inner and outer edges curved. 
Referring now to FIG. 2, there is shown a sectional side view of a 
dynamoelectric machine having a rotor 12 as described, for example, in 
connection with FIGS. 1, 3A, 3B, 4A and 4B. The winding 17 is shown on 
pole 14 between pole collars 30 and 31. One coil bracket 19 is shown 
midway between the ends of pole member 18. A baffle 25 is shown at each 
end of pole member 18. 
Stator 33 has a stator core 34 with a winding 35 having end turns 36. The 
stator core 34 has a plurality of radially extending, axially spaced, 
ventilation ducts 37. A stator frame 40 includes stator core support 
plates 38, stator core flanges 41, stator core bars 42, and space blocks 
43. Bearing bracket assemblies 44, represented schematically, include 
bearings for supporting shaft 10 to provide for rotational movement of the 
rotor. Stator structures of this form are known. 
When the machine is operating, the flow of cooling air (or other cooling 
gas) is indicated by arrows 45. The air flow is indicated by arrows 45 for 
only one half of the machine; the air flow is the same for the other half. 
The air is introduced from a passageway 39, indicated by broken lines, 
normally from atmosphere, although the passageway 39 could be connected to 
receive recirculated air as is known. 
There are frequently axially extending air passages in rim 11 as is 
indicated by broken line 46 representing air flow through such a passage 
and through openings in rim 11 into the interpolar spaces to improve the 
cooling of the inner parts of windings 17. The air flow passes from the 
interpolar spaces radially outwards through air gap 47 between the 
periphery of pole members 18 and the stator core 34, and then through 
ventilation ducts 37 into exhaust region 48 which is open to atmosphere. 
Referring now to FIGS. 5A, 5B and 5C, there are shown graphs of air flow 
against axial positions along a stator core giving relative air flow 
through the ventilation ducts 37 (FIG. 2). In FIG. 5A, a line 50 indicates 
air flow through the ventilation ducts in a machine with a salient pole 
rotor having one coil bracket, centrally located in each interpolar space, 
and no baffle 25 (FIGS. 1, 2, 3A and 3B, for example). The air flow tends 
to be greater in the central region where the air flow from each end 
meets. This is increased to some extent by the coil bracket which tends to 
act as a fan blade. 
FIG. 5B has a line 51 representing air flow through ventilation ducts at 
different axial positions where the rotor has five coil brackets in each 
interpolar space, spaced along the rotor. Because each coil bracket acts 
somewhat as a fan blade, the air flow is slightly greater in the region of 
each coil bracket. In fact, suitable placing of the coil brackets where 
the air flow is a little less tends to distribute the flow as desired. In 
addition, the change in air flow contributed by a coil bracket can be 
altered to some extent by changing the thickness of the central portion 20 
(FIG. 1) of the coil bracket. The effect of the coil brackets can be 
determined by experiment. 
In FIG. 5C the line 52 represents air flow in the ventilation ducts of a 
machine similar to the machine where the air flow is represented by FIG. 
5B, but with a rotor 12 which has baffles 25 on the rotor as described in 
connection with FIGS. 1, 2, 3A and 3B, for example. The air flow in the 
ventilation ducts 37 (FIG. 2) which are adjacent the ends of the stator 
has been increased. The addition of the baffles of the invention does not 
make the air flow in the end ventilation ducts equal to the air flow 
through the ducts in the central part of the stator, but it does increase 
it. 
In one example, a dynamoelectric machine model with a salient pole rotor 
according to FIGS. 1 and 2 was rotated at 450 rpm and the static pressure 
was measured, in inches of water, at the two end ventilation ducts and at 
several intermediate ventilation ducts (at two radial positions in each 
measured duct). Without baffles installed, the static pressure at the end 
opposite the drive end was 0.10 inches of water and at the drive end was 
0.12 inches of water. With baffles according to the invention installed at 
both ends of each interpolar space, the static pressure measured at the 
end opposite the drive end was 0.45 inches of water, and at the drive end 
was 0.54 inches of water. The static pressure at the intermediate points 
had also increased. As the static pressure is a determining factor in air 
flow, other things being the same, the baffles would result in an increase 
in air flow through the end ducts. Thus, the increased air flow not only 
improves the cooling of the rotor, but improves the cooling of the end 
regions of the stator. 
It is believed that the following description explains how the baffles 
improve the air flow and the cooling of the rotor and of the end regions 
of the stator. In a salient pole rotor, the pole members themselves tend 
to move air radially outwards. The coil brackets tend to increase the 
outward flow in the region where they are mounted. Thus, the air flows 
into the interpolar spaces from each end and changes direction to flow 
radially outwards through the air gap and the stator ventilation ducts. 
The axial air velocity tends to be greater at the bottom of each 
interpolar space, and a typical air velocity profile for the rotor 
interpolar area is shown in FIG. 6A. In reality, there tends to be some 
back flow or reverse flow, as shown by the air velocity profile of FIG. 
6B. The air entering the interpolar area is acted upon by several forces, 
mainly centrifugal force and coriolis force. The interaction of the 
centrifugal force, F.sub.t, represented by the equation F.sub.t 
.alpha.r.multidot..omega..sup.2 and the coriolis force, F.sub.c, 
represented by the equation F.sub.c .alpha.V.sub.a .omega. determine the 
flow direction. In the above equations, r is the radius from the axis, 
.omega. is the angular velocity, and V.sub.a is the axial velocity of the 
air. 
At the shaft the axial velocity, V.sub.a, is very high and it decreases in 
magnitude when moved radially outwards, reducing to zero and then 
reversing as shown in FIG. 6B. The tangential velocity of the air, 
V.sub.t, is low near the shaft and increases when moved radially outwards. 
Therefore, the typical velocity vectors at the shaft are as shown in FIG. 
7A and at the air gap are as shown in FIG. 7B. V represents the relative 
resultant velocity. 
By placing a baffle at the end of the interpolar space adjacent to the air 
gap, V.sub.a is reduced and the flow becomes substantially radial as shown 
in FIG. 7C. Hence the air is directed almost radially outwards into the 
first few ventilation ducts in the stator. The baffles also tend to 
increase the radial and tangential velocity components because the baffles 
are a rotating surface. This combination or interaction tends to increase 
the air flow in the end regions of the rotor and of the stator. 
It is believed the preceding description adequately explains the invention.