Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-12-11
2001-03-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C105S053000, C180S065600, C318S254100, C318S661000
Reexamination Certificate
active
06198196
ABSTRACT:
BACKGROUND
The present invention places itself in the field of the electric machines with a discoidal structure. It relates more particularly to a method of and a device for the compensation for magnetic pull forces between the rotor and the stator of such a machine.
The electric machines with a discoidal structure comprise at least one disc-shaped stator held on a casing and the central portion of which is generally hollowed out as well as a rotor also in the shape of a disc mounted onto a shaft the axis of which coincides with that of the stator disc.
One may in particular cite the patent FR-2,583,231 which describes a discoidal machine in which the rotor disc is placed between two stator discs, the windings of the rotor and stator discs being placed on confronting faces.
One may also contemplate a discoidal machine comprising a stator disc with a double face placed between both discs of the rotor.
In both cases the faces of the stator and of the rotor are separated by air gaps. At the time of the mounting, the dimensions of these air gaps are provided to be approximatively equal. In this type of machine, the rotor may exhibit axial offsets with respect to the stator in view of the mechanical machining and mounting tolerances of the different elements. One also finds that the dimensions may vary owing to the thermal expansions of the materials and mechanical forces.
The flux which flows through the poles of the discoidal machine comprises two components: the main flux and the secondary flux also called interpolar flux.
The main flux axially extends through each disc. The generated forces therefore have opposite directions and the resultant of these forces theoretically is zero.
The inteirpolar flux comprises variable components as a function of the number of poles and of the dimensions of the air gap. It generates forces which in theory counterbalance one another.
However due to the fact of the dimensional variations appearing inside of the discoidal machine, the forces generated by the interpolar fluxes at the level of each air gap do not counterbalance one another in practice.
Thus during the operation of the machine, substantial axial forces appear on the rotor and the stator, these forces being due to the differences of inteipolar flux on each face of the rotor or stator.
These forces may result in the deterioration of the discoidal machine.
SUMMARY OF THE INVENTION
The invention has as its object to cope with these inconveniences by proposing a method of compensation for the magnetic pull forces inside of an electric machine with a discoidal structure comprising at least three rotor and stator discs disposed coaxially and foiming two air gaps, the external discs being of a type different from that of the internal disc.
The method consists in:
measuring for each one of the two air gaps a same magnitude representative of the value of the air gap,
comparing the said magnitudes and
modifying the fluxes at the level of the air gaps to balance the value of both air gaps and thus to compensate for the magnetic pull forces.
In a first mode of putting into practice, the fluxes of the air gaps are modified by feeding the stator faces in an independent manner.
In a preferred manner the feeding of the stator faces is carried out through the medium of converters each one associated with one face of the stator disc.
In a second mode of putting into practice, the fluxes of the air gaps are modified by generating an additional flux at the level of each air gap.
In a preferred fashion, the said additional flux is generated by currents circulating in at least one inductor.
According to a first alternative embodiment of the method, the said magnitude representative of the value of the air gap is an electromagnetic magnitude, in particular the polar flux, the interpolar flux or the induction.
According to a second alternative embodiment of the method, the said magnitude is a mechanical magnitude in particular the mechanical deformation of the discs or the relative displacement between a rotor disc and a stator disc.
The invention relates also to a device for the compensation for the magnetic pull forces inside of an electrical machine with a discoidal structure comprising at least three rotor and stator discs disposed coaxially and forming two air gaps, the external discs being of a type different of that of the internal disc, characterized in that it comprises:
for each air gap, a means for the measurement of a magnitude representative of the value of the said air gap, disposed on one of the faces of one of the discs forming the said air gap, the said magnitude being identical for both measurement means, and
a control unit the inputs of which are connected to the said measurement means and the outputs of which are connected to balancing means, the output signals from the control unit driving the said balancing means so as to balance the fluxes between both air gaps and thus to compensate for the said pull forces.
In a first alternative embodiment, the balancing means are constituted by converters associated each one with one stator disc face.
In a second alternative embodiment, the balancing means are constituted by at least one inductor for each air gap, disposed on one face of one of the discs forming the said air gap.
The following characteristics may also be taken into consideration isolately or according to all their technically possible combinations
some inductors are the windings of the rotor disc or discs;
the control unit comprises:
a regulation module receiving at the input the signals issued from the measurement means and
a drive module connected to a device for feeding with current and to the said inductors, the regulation module delivering a signal to the drive module for diverting the current issued from the feeding device into the said inductors,
the regulation module comprises
means for converting the signals issued from the measurement means into continuous signals and,
means for comparing the said continuous signals, connected to an integral regulation device,
each measurement means is constituted by at least one turn,
each measurement means is constituted by at least one Hall effect sensor,
each measurement means is constituted by at least one Foucault current displacement sensor,
each measurement means is constituted by at least one strain gauge,
the compensation device comprises a safety systeme generating an alarm or the emergency stop of the machine when the output of the comparator means is above a determined threshold value.
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Bondu Alain
De Simon Eddy
Milet Yves
Dinh Le Dang
Dougherty Thomas M.
Jeumont Industrie
Leydig , Voit & Mayer, Ltd.
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