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THE PRIOR ART
Submersible pumps are known utilizing so-called "Wet motors" in which the
stator as well as the rotor of the motor is immersed in the liquid being
conveyed. Such pumps have in the past been utilized in deep wells and
cooling of the pumps has been effected by two stages. First the heat of
the windings is transmitted to the motor housing by the thermal
conductivity of the liquid being pumped and then the heat of the housing
is carried away by the circulated liquid. This cooling process involving
two stages has been necessary because such submersible pumps usually have
liquid lubricated bearings. It is desirable in such pumps to insure that
no flow of liquid takes place over the bearings to eliminate the
possibility of sand or other abrasive material contaminating the bearings.
Split tube type submerged pumps have also been utilized in which the
windings of the stator are hermetically sealed from a rotor which is
disposed in the liquid being conveyed and where the stator is separated
from the rotor by a magnetically pervious housing structure. A
disadvantage of split tube type pumps has been that the magnetic gap
between the stator and the rotor has to be comparatively large which in
turn has an adverse effect on the weight per unit power of the motor and
upon its efficiency.
A further disadvantage in both the split tube type pump and the so-called
"wet motor" type pump is that they are inappropriate for use in pumping
liquids having high operating temperatures since such temperatures cause
break down of the insulation of the conductive materials of the motor.
Also the chemical properties of the liquid being pumped becomes a concern
in wet motor type pumps since the liquid may attack the insulation.
It has become a problem particularly with nuclear reactors which operate at
extremely high temperatures to provide for pumps which may operate under
high temperature conditions at which conventional pumps would normally
fail because of the effect of the temperature on the insulation of the
windings.
OBJECT OF THE INVENTION
It is an object of the invention to provide for a submersible electric pump
which may operate at extremely high temperatures and which will utilize
the liquid being pumped to provide the necessary cooling for the motor. It
is a further object to provide for a submersible electric pump which
eliminates need for any insulation such that the pump may be immersed in
liquids which would normally attack insulation materials.
DESCRIPTION OF THE INVENTION
The invention solves the problem in that one side of each individual coil
of each coil group of an electric motor is connected via a common star
point at a further star point common to all coil groups and voltages are
applied to their other sides, which increase from the coil having the
smallest width to the coil having the largest width of each coil group by
amounts which eliminate short circuiting of adjacent conductors in the
medium being conveyed. By taking advantage of the fact that various liquid
media and particularly water have certain insulating properties, the
invention provides operating voltages between adjacent conductors to be so
small that the insulating properties of the media being pumped eliminates
short circuiting or arcing between adjacent conductors.
Having regard to the small voltages which are applied to the individual
coils, the cross-section of these conductors, of which the coils are made
up, have to be of appropriate size, so that the coils have adequate
structural stability. By reason of this structural stability it is
possible, by means of spacer members or spacing means, to maintain the
individual turns of the coils spaced from each other and from the pole
teeth. If the medium being conveyed is hot water, the spacing means may
take the form of coatings of glass or mineral fiber fabrics which, while
not being waterproof, nevertheless provide the spacing of the winding
turns relative to each other and to the pole teeth, while the insulating
function itself is performed by the medium being conveyed, namely the
water. In this construction, voltages below 40 volts have been found to be
adequate at spacings between the conductors of approximately 1mm.
In reactor vessels, glass fiber fabrics wrappings are destroyed on account
of the high neutron density and on account of the high temperatures. In
this case the invention envisages providing the spacing of the turns
relative to each other and to the pole teeth and quite generally the
spacing of the electrical conductors relative to each other by use of
ceramic spacer means. These spacer means may be ceramic spheres, which are
inserted matingly in recesses provided in the conductors. Preferably in
this case voltages between adjacent conductors are chosen which are below
20 volts, so that metallic contaminants in the stream of the medium being
conveyed cannot lead to short circuits between the conductors. Preferably
when operating at voltages of this order of magnitude coils are used in
the coil groups with only one turn per coil.
The invention takes advantage of the large cross-sections of the conductors
in the supply leads to the stator of the pump motor are used for
suspending the pump, the supply leads preferably having a section which is
such that they are of maximum rigidity to resist bending. Utilizing the
supply leads for the purpose of suspension simplifies the construction
costs for the pump in reactor design considerably. An advantage of a pump
motor constructed according to the invention and when suspended in the
stream of medium being conveyed is that it eliminates the need of a shaft
extending through the wall of the reactor vessel so that the problem
associated with penetration of the reactor vessel and sealing of the shaft
is eliminated. The invention is of great importance for reactor design
because high pressures prevail in reactors and this sealing poses
extremely difficult technical problems not only from the point of view of
sealing but also from the point of view of the design of the reactor
vessel.
Fundamentally however the new pump may be used in applications in which it
was previously difficult to use a submersible motor because of
installation problems. Thus a pump according to the invention may for
example also be used in conventional power station boilers for circulating
the water or also for conveying the water; may be used in pipe systems
having extremely contaminated liquids or may also be used for conveying
solvents which ordinarily attack organic insulation material.
The number of the supply leads to a stator of a motor according to the
invention equals q m, where q is the number of coils per coil group and m
the number of phases. If, for example, in a practical embodiment, each
coil group includes three coils and a three-phase supply is used, nine
supply leads per pump motor are required. By making each supply lead of
appropriate section, these supply leads may be combined into a bundle of
leads in which the individual leads are kept from each other at definite
spacings by spacer means. Within the region of these spacer means, these
bundles may for example be held by metal rings, which themselves are
spaced from the leads by additional spacer means, so that the supply lead
bundles provide very stable suspension devices.
The feature of the invention, according to which one end of each of the
coils of a coil group has a voltage supplied to it such that the voltages
increase by definite amounts from the coil of the smallest width to the
coil of largest width, has the effect that approximately the same current
flows through each coil in each coil group. This result is surprising to
the extent that it has been found that when all the coils of a coil group
are connected in parallel practically only the coil of smallest width i.e.
the innermost coil of a coil group, conducts current. This relationship
will be explained in greater detail in the description of the drawings.
Thus, in an arrangement in which all coils of a coil group are connected
in parallel, given the same amount of winding material, the flux density
which can be achieved in the gap is considerably lower than with an
arrangement in accordance with the invention.
The invention further relates to a transformer for supplying an electric
motor embodying the invention whose stator has a secondary winding which
is sub-divided into winding sections. When using a conventional
transformer for supplying an electric motor in accordance with the
invention, in which the individual coils are connected to different
tappings of the secondary winding, the current densities would, having
regard to the high currents required, reach considerably higher values in
some parts of the winding than in other parts, so that either the
cross-sections of the winding would have to differ from each other
considerably in different places or, if equal cross-sections are used, the
winding would be substantially over-dimensioned in certain places.
The invention therefore provides a transformer for supplying a motor
embodying the invention, in which different sections of the winding
embrace different core cross-sections and these winding sections have one
end connected to a common star point and the other end connected to the
coils of the stator. Appropriately the numbers of the turns of the
windings from which the individual voltages are tapped off are equal, the
core cross-sections of the secondary portion of the transformer embraced
by the individual windings having a particular relationship to the
voltages tapped off the individual windings. The core sections which are
embraced by the individual windings, are in this arrangement magnetically
connected in parallel. When the supply of the individual coils of the coil
groups of a motor made according to the invention are supplied by the
individual windings of the transformer made according to the invention,
the currents passing through these individual windings are approximately
equal. By reason of the differential power outputs resulting from the
different core cross-sections, the core of the secondary portion therefore
has a magnetic flux passing through it homogeneously and maximum
utilization of the core iron is thereby achieved.
DESCRIPTION OF THE DRAWINGS
The invention will now be explained with reference to the drawings:
FIG. 1 shows a diagrammatic view and partly in section, a boiling water
reactor having pumps with motors constructed according to the invention;
FIG. 2 shows diagrammatically a section through the lower part of the
boiling water reactor shown in FIG. 1, with, however, only the most
important elements shown;
FIG. 3 shows a pump in a reactor with a motor according to the invention,
partly in section, and partly in elevation, the motor being located in a
housing;
FIG. 4 shows a further embodiment of a pump according to the invention
partly in section and partly in elevation, the entire motor being disposed
without a housing, in the stream of the conveying mechanism;
FIG. 5 shows partly in elevation and partly in cross-section a similar pump
to that shown in FIG. 4, with a flap control mechanism according to the
invention, which automatically prevents flow taking place through the pump
when the pump impeller is not in operation;
FIG. 6 shows diagrammatically a plan of a stator of a motor according to
the invention with teeth designated by Roman numerals and the layout of
the individual coils and coil groups which are inserted into the teeth;
FIG. 6a shows the ideal spatial distribution of the magnetic flux density
in the air gap produced by one phase of a winding according to the
invention;
FIG. 6b shows, by way of comparison to the arrangement shown in FIG. 6a
according to the invention, the spatial distribution of the magnetic flux
density in the air gap produced by one phase of the winding when the coils
of a coil group are connected in parallel;
FIG. 7 shows a circuit diagram for a two-pole stator with 18 pole teeth of
the type shown in FIG. 6 and the connection of the stator to a transformer
according to the invention;
FIG. 8 shows a plan view one phase of the winding of a stator for a
four-pole motor according to the invention with four coil groups, each of
which has three coils of different widths;
FIG. 8a shows a perspective view of a complete winding of a stator
connected to supply leads and which has a total of three phases where the
winding is of the kind shown in FIG. 8;
FIG. 9a is a partial sectional view of a transformer constructed according
to the invention;
FIG. 9b is a partial sectional plan view of the transformer of FIG. 9a; and
FIG. 9c is an end view of the transformer of FIG. 9a taken along lines
IXc--IXc.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The boiling water reactor shown in FIG. 1 has a pressure vessel D which
encloses the core K and the envelope chamber M. In the envelope chamber M
pumps P embodying the invention are located, in which the rotor, the
stator and the pump impeller each constitute a unit which are suspended by
the supply leads Z in the envelope chamber.
FIG. 2 shows again diagrammatically the lower portion of the reactor shown
in FIG. 1. The control rods 2 are surrounded by an envelope 3. The pumps P
are located in the envelope chamber M. The through-flow takes place in the
direction of the arrows 6 and 6' i.e. in a downward direction in the
envelope chamber M and in an upward direction in the core chamber of the
reactor. The pumps P are connected to the upper portion of the pressure
vessel D by their connecting leads Z and are seated in a ring 8 which is
provided with an aperture for each pump.
FIG. 3 shows a pump of the kind used in the reactor shown in FIG. 2, partly
in elevation and partly in section. The pump is located between the
envelope 3 and the reactor vessel D and is seated in an aperture 9 of the
annular sheet metal member 8. The stator of the motor has radially
disposed sheet metal elements 20 which form pole teeth and whose frontal
sides 20' together with the armature 22, define a magnetic gap 21. The
magnetic return path is provided by a packet 23 of sheet metal discs. The
coils 24 each have one or two turns only. The circuit of the conductors is
completed inside the motor. The supply leads 25 which together form the
conductor bundle 7 in FIG. 2 lead to the upper region of the pressure
vessel D and form the suspension of the pump. The pump can be withdrawn in
a vertical upward direction by means of the conductor bundle. The pump
stator comprising the parts 20, 23, 24 may be surrounded by a stator
housing 26, which has a corrugated rib profile 27.
A secondary pump 28, which in principle is of the same construction as the
pump motor, may provide circulation of the cooling water inside the
stator. The cooling water flows through the stator in the direction of the
arrows 29, 30, 31.
A bearing column 32 has a dish 33 with a concave region and an annular
convex region 33'. The pump impeller 34 with its axial blade ring 35 forms
a unit with the armature 22 and the cage winding 37 which is joined to a
dish 33". A bearing sphere 39 is enclosed between the dishes 33 and 33". A
collar 40 is provided as a back-up in the convex region 33', so that the
rotor cannot drop even when the pump is switched off. During start-up the
rotor is, by reason of the magnetic forces and the thrust of the water
being discharged and flowing in the direction of the arrow 41, pressed
against the sphere. The water enters through the radial blade ring 43 in
the direction of the arrow 41'. A bellows 44 provides a pressure relief
volume equalization means between the interior and the exterior of the
motor housing. A separating wall 21" of non-magnetic material may be
provided in the gap 21.
The pump shown is also suitable for conveying liquid metal, since the
stator with its winding 24 is accommodated in a sealed housing 26. The
latter is also separated from the fluid being conveyed at the magnetic gap
by the separating wall at 21". Inside the housing 26 a liquid is provided
which has adequate insulating properties. The latter is caused to
circulate by means of the cooling liquid circulating pump 28, so that the
heat representing the losses is circulated by means of the flow of the
cooling medium 29, which may for example be diphenyl or thiokol or some
other thermally stable liquid, and is given off through the wall 27 to the
liquid metal.
FIG. 4 shows a similar view to that of FIG. 3 of a pump having a motor
embodying the invention, whose stator is suspended in the envelope chamber
M. The armature 22, which forms a unit with the cage winding 37, is of the
same construction as in the embodiment shown in FIG. 5. It is supported
via the bearing sphere 39 in the dish 33 which is supported relative to
the stator by the column 32. A ring 32' adapted to be screwed on the
column 32 backs up the dish 33', which is joined to the armature 22 via a
screw connection 33", a column 34 and a further screw connection 22'. In
this way the rotor is prevented from dropping when the motor is switched
off. The pole teeth are formed by radially disposed sheet metal elements
20 and bound the magnetic gap 21 by the surfaces 20' facing the armature.
The various coils of the winding 24 have one turn only. The magnetic
return path is provided by annular sheet metal packets 23 and 23'. The
motor is suspended by the supply leads 25 which are united to form a
bundle. By contrast with the motor shown in FIG. 3, the stator, in the
case of the example according to FIG. 4, is located in the stream of
liquid being conveyed and is cooled by it. Through apertures 45 and 46 the
medium being conveyed can flow into the stator chamber and cool the
winding. Thus neither a pump housing nor a stator housing is provided. The
inlet blade ring 43 is secured to the stator.
In the embodiment shown in FIG. 5 the stator comprises the pole teeth 50,
which again are formed by radial sheet metal elements. The magnetic return
path is provided by annular sheet metal packets 51 and 51'. The coils of
the winding 52 have one turn each. They are connected to the supply leads
53, which again form a conductor bundle, by which the pump is suspended.
Through apertures 54 and 55 the medium being conveyed can flow into the
stator chamber and cool the stator. The pole teeth form the magnetic gap
57 by their frontal surfaces 56. The rotor comprises an iron core 58, bars
59 and short circuiting rings 60 and 61 of a cage winding. The surface of
the rotor facing the air gap 57 lies in the region of the spherical ring.
The rotor is, as in the case of the embodiments shown in FIGS. 3 and 4,
supported via a sphere 62, a dish 63 secured to the stator as well as a
dish 64 secured to the rotor. This dish 64 is arranged on a column 65
which is joined to the rotor by screw connections. In the same way as
shown in FIG. 4, a ring 63' serves to prevent the rotor from dropping when
the pump is not switched on. The guide blade ring 66 is secured to the
stator, while the pump blade ring 67 is located on the rotor. The medium
being conveyed which flows around the stator is conveyed in the direction
of the arrows 69 through the pump and enters a terminal housing 70 and
leaves through slits 71. The bearings 72 and 72' in the terminal housing
support a valve plug, which has a slightly conical inner surface 74 and a
cylindrical outer surface 75. The outer surface has slits extending in the
axial direction, which are able to register with the slits 71 of the
terminal housing 70. The regions 75' between the slits 71 extend in the
azimuth direction somewhat further than the slits 71, i.e. the regions
between the slits 71 are somewhat wider than the latter. Likewise the
bridges 77 between the slits in the outer cylinder 75 of the valve plug
are somewhat wider than the slits 71 of the terminal housing.
A guide blade ring 78 is secured to the plug 73, the blades of the former
being so disposed that the plug is rotated in one direction until it
reaches an abutment, by the swirl of the hydraulic medium. In this
position the slits of the plug register with the slits of the terminal
housing and the bridges of the plug with the bridges of the terminal
housing. This means, that when the pump is switched on, the flow can take
place freely in the direction of the arrow 69 through the pump chamber and
in the direction of the arrow 80 out of the latter. If now the flow is
interrupted for any particular reason, a spirally coiled spring 81, which
pre-tensions the plug in the direction opposite to that in which it is
rotated by the swirl of the flow, causes this plug to be rotated in the
opposite direction up to a second abutment, in which position the slits in
the outer cylindrical walls 77 then register with the bridges 75 of the
terminal housing on the one hand and the bridges between the slits in the
outer cylindrical wall of the plug register with the slits 71 of the
terminal housing on the other hand. In this position the valve defined by
the terminal housing and the plug is closed so that, for example, if the
pump trips, no flow produced by adjacent pumps can take place through this
valve. In this way the possibility of back-flow through pumps which have
tripped is eliminated.
It is emphasized that the bearing for the plug can be adjusted by means of
a screw 82 which presses on the bearing dish 83. Relief bores 84 are
provided for pressure equalization. Outwardly conical feet 85 facilitate
insertion of the pump into the sheet metal ring 86 during assembly.
Instead of the screw 82, it is also possible to provide alternative
arrangements for adjusting the bearing.
FIG. 6 shows diagrammatically a stator of a motor according to the
invention in plan view. The stator is intended for a two-pole machine and
has 18 pole teeth I--XVIII. The broadest coil of a coil group embraces 8
pole teeth, the smallest coil of each coil group 4 pole teeth and the
intermediate one 6 pole teeth each. Thus 3 coils per coil group and 2 coil
groups per phase are provided in this two-pole machine. For connection to
a three-phase supply, 3 phases are required. Three different phases are
indicated by continuous lines, interrupted lines and dotted lines. It can
also be seen how each coil is connected at one end to the star point 90.
For the stator z .times. m (q = number of coils per coil group, in this
case 3, and m = number of phases in this case also 3), i.e. 9 supply leads
are required, which are designated 1 to 9.
As can be seen from FIGS. 6 and 7, one end each of the coils of a coil
group are subjected to a voltage which decreases from the coil of greatest
circumferential width in each group to the coil of smallest
circumferential width. The voltages in the 3 supply leads to each
individual coil group are of the same phase. Again the coils of equal
width in different coil groups and different phases are subjected to
voltages of the same magnitude but of different phase. The magnitudes of
the partial voltages required for supplying the individual coils of a coil
group are, at a first approximation, related as the chord factors sine
(2.sub.p 90.degree. Z.sub.s /Z) (p = number of pole paris, Z.sub.s =
number of teeth embraced by one coil, Z = total number of teeth of the
stator) of the coils concerned.
FIG. 6a shows a developed representation of the ideal spatial distribution
of the magnetic flux density in the air gap produced by one phase of the
winding in accordance with the invention. It is based on the winding
embodying the invention in accordance with FIG. 6 or FIG. 7 with 3 coils
per coil group and 2 poles.
By comparison, FIG. 6b shows in the same manner as FIG. 6a the spatial
distribution of the magnetic flux density in the air gap in the case of
all coils of a coil group being supplied with the same voltage, as becomes
necessary when these coils are connected in parallel. It necessarily
follows according to the law of induction in the case of parallel
connection of the coils of a coil group and their supply with the same
voltage that all coils of a coil group have the same magnetic flux. This
however is possible only when only the innermost coil of a coil group
conducts current, while all the coils of greater width remain
substantially without current. This disadvantage is eliminated by the
winding in accordance with the invention.
FIG. 7 shows the supply for a winding according to FIG. 6 embodying the
invention, via a transformer with the primary winding phases 92', 92",
92'", and a secondary winding with the partial windings 93', 94', 95' for
the first phase, 93", 94", 95", for the second phase and 93'", 94'", 95'"
for the third phase. Of the winding of FIG. 6, only the first phase with
the teeth I-XVIII, the star point 90 and the supply leads 1, 2, 3, are
shown in developed representation. In the same way the second phase is
connected by the supply leads 4, 5, 6 and the third phase by the supply
leads 7, 8, 9.
FIG. 8 shows one phase of a winding for a motor embodying the invention
with 4 coil groups, each of which has 3 coils. This phase is intended for
a 4-pole machine having a stator with 36 pole teeth. One side of each coil
group is connected to a star point 100 and its other side to a conductor
101', 102' or 103' respectively. These conductors are again supplied with
voltages of different magnitude, namely the conductor 101' with the
greatest voltage and the conductor 103' with the smallest voltage. In the
case of a three-phase supply, 3 phases are required, as shown in FIG. 8,
which are relatively displaced by 60.degree. in space and slid over the
pole teeth. Such an embodiment is shown in FIG. 8a, in which the phases
104', 104" and 104'" are arranged in three planes one above the other.
These phases are constructed in the same manner as shown in FIG. 8 and as
shown partly in section. The supply leads to the phases concerned are
indicated respectively as 101', 102' and 103' and 101", 102" and 103". The
supply leads to the third phase are not shown in FIG. 8a.
FIGS. 9a to 9c show three views of a practical embodiment of a transformer
according to the invention. The primary winding 105', 105", 105'"
surrounds the core consisting of three portions 106, 107, and 108, while
the secondary windings 109', 109", 109'"; 110;, 110", 110'"; 111', 111",
111'" each surround only one portion of the core, viz. 106, 107 and 108
respectively.
In this way different portions of the winding surround core portions of
different cross-section. If the windings 109, 110, and 111 have the same
number of turns, preferably 1 or 2, then the voltages applied to these
windings are proportional to the cross-sections of the portions to which
the windings are applied.
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