GB2045983A - Electrical Generator Voltage Regulation - Google Patents

Abstract

By means of the control windings (16), the reluctance of ferromagnetic material in the magnetic-circuit is altered, whereby the flux in the generator, and hence the output voltage, made be regulated. The output windings and the control windings (16) are on the stator with the control winding connected to a d.c. source. Alternatively, the output windings and the control windings may be on the rotor and in this case control current is applied to the control windings by conventional means such as slip rings. Feedback from the rectified generator output may be compared against a reference voltage and cause an amplifier (28) to vary the DC fed on the control windings. Alternatively, (Figure 3e, not shown) as long as the output voltage does not exceed a given voltage no control current is generated, otherwise feedback causes abrupt saturation to reduce the output current to prevent demagnetisation of the rotor. <IMAGE>

Description

SPECIFICATION Electrical Generator The present invention relates to rotary machinery and more particularly to rotary machinery of the electrical generator type which incorporates control windings employed for regulating the magnitude of the output voltage developed by the electrical generator.

In electrical generators of the character described, means, typically a rotor assembly, are provided for producing a magnetic field. The rotor assembly is typically rotated by any suitable primary source, such as a motor. The rotation of the rotor assembly causes the magnetic field to cut across output windings of the stator assembly cooperating with the aforesaid rotor assembly wherein the moving magnetic field induces an electrical voltage in the output windings, which voltage is a function of the strength of the magnetic field, and the rotating speed of the rotor assembly.

The major contributor to the voltage generated in the stator windings is the magnitude of the flux field. If a permanent magnet is used in the field structure and it is desired to vary the voltage for any reason, there is no convenient means presently known for accomplishing this result.

This is in contrast to electrical generators of the wound rotor type wherein the flux may be controlled by controlling the magnitude of the current to the rotor winding.

As an alternative, the output of the electrical generator may be controlled by means of a power regulator. The disadvantage of this approach is that the power regulator must monitor full output power and also requires costly complicated circuitry.

In accordance with one aspect of the present invention there is provided a method of regulating the output voltage from an electrical generator by regulating the total magnetic fluxhe generator by means of d.c. saturation of portions of the iron paths of the field iron through which said flux is concentrated.

According to a second aspect of the present invention there is provided a machine comprising a rotor assembly, a cooperating stator assembly, said rotor assembly and stator assembly being rotatable to each other, one of said rotor and stator assemblies comprising means for generating a magnetic field directed toward the other one of said assemblies, the remaining one of said rotor and stator assemblies comprising a member made of a material having a non-linear permeability, first winding means on said member for generating an electrical output responsive to the movement of said magnetic field past said first winding means due to the relative rotation between said rotor and stator assemblies, and control means including DC power means and control winding means on said member responsive to said DC power means for introducing magnetic flux of a predetermined magnitude in said member to alter the level of the output developed by said output winding means.

Preferably, the member is annular shaped.

The rotor assembly may be comprised of output and control windings mounted upon a ferromagnetic core, and in this case control current may be applied to the control windings by conventional means such as slip rings.

Alternatively, in a toroidal shaped member, the output and control windings may form part of a stator assembly.

The control windings are connected with there pluralities in opposition so that any voltage is developed within the windings due to the magnetic field sweeping the control windings is effectively cancelled.

The permanent magnet member may form part of the stator. The rotor assembly would then be comprised of output and control windings mounted upon a ferromagnetic core. Control current may be applied to the control windings by conventional means such as slip ings.

As an alternative, in a toroidal shaped member the output and control windings may form part of the stator assembly.

The control windings are connected with their polarities in opposition so that any voltages developed within the windings due to the magnetic field sweeping the control windings is effectively cancelled.

According to the present invention, there is provided an electrical generator which comprises a rotor assembly and a cooperating stator assembly, the rotor and stator being rotatable relative to each other, one of the rotor and stator assemblies comprising means for generating a magnetic field directed toward the other one of said assemblies, the remaining one of said rotor and stator assemblies comprising a member of a material having a non-linear permeability, output winding means on the member for generating an electrical output responsive to the movement of the magnetic field past the output winding means due to the relative rotation between the rotor and stator assemblies, and control means including DC power means and control winding means on the member which are responsive to the DC power means for introducing magnetic flux of a desired magnitude in the member to alter the level of the output developed by the output winding means. Preferably, the member is annularly shaped.

In order that the invention may be fully understood, it will now be described with reference to the accompanying drawings, in which Figure 1 a shows a simplified schematic of the three-phase permanent magnet alternator of conventional design.

Figure 1 b shows a detailed portion of the stator of the three-phase type which may be employed in the electrical generator of Figure 1 a.

Figure 2a shows a portion of the stator iron of the type shown in Figure 1 b showing the manner in which the control windings of the present invention may be arranged.

Figure 2b shows a circuit diagram of an alternator of the permanent magnet rotor type utilizing toroidal output windings and incorporating the principles of the present invention.

Figure 2c shows an alternator of a modified designal as compared with that shown in Figure 2a and employing skein type output windings.

Figure 2d shows a detailed view of a portion of an alternator of another preferred embodiment of the present invention wherein the control windings of the present invention are incorporated as part of the rotor assembly.

-Figure 3a shows a schematic diagram of a three-phase alternator incorporating circuitry for providing full wave rectification of the threephase output.

Figure 3b shows a schematic diagram of a feedback circuit which may be employed with the alternator of the present invention for controlling the magnitude of the current delivered to the load serviced by the alternator.

Figure 3c shows a schematic diagram of a feedback circuit which may be employed as a circuit protective device with the alternator of the present invention.

Figure 1 a shows a simplified schematic diagram of a three-phase AC electrical generator or alternator 10 which may be adapted to employ the present invention. The alternator is comprised of a permanent magnet type rotor 11 adapted to be rotated about its central axis represented by dotted line 1 a. The rotor is typically surrounded by a stator assembly comprised of an annular shaped member adapted to serve as a means for concentrating the magnetic flux developed by the permanent magnet rotor 11 into a predetermined path or paths. In the three-phase alternator of Figure 1 a, three separate windings 1 2a, 1 2b and 1 2c are wound about this member. First ends of each of the windings are electrically connected to a common or neutral terminal as represented by common conductor 13.The opposite terminals 1 2all, 1 2b-l and 1 2c-l are adapted to be connected to a three-phase load (not shown for purposes of simplicity).

The stator output windings 1 2a through 1 2c are preferably located within slots of the stator iron as shown best in Figure 1 b. Figure 1 b shows a portion of the alternator 10 of Figure 1 a in greater detail.

The annular shaped member 14 is preferably formed of a suitable ferromagnetic material which may, for example, be silicon steel. However, any other high permeability material may be utilized.

Laminated plates are preferred in order to minimize eddy current losses. The member 14 will hereinafter be referred to as the stator iron and this term is intended to incorporate both solid and laminated structures.

The stator iron 14 is provided with a plurality of slots 1 4a, each adjacent pair of slots defining there-between a tooth 14b, all of which slots and teeth are substantially identical to one another.

Portions of the output windings, 1 2a and 1 2b are shown as being wound about selected ones of said teeth. The electrical connections of the output windings have been omitted for purposes of simplicity.

The teeth 1 4b all extend radially inward and their innermost surfaces are closely spaced to the poles of the permanent magnet rotor 11 to provide a small but uniform sized air gap therebetween.

Figure 1 b shows a magnetic north pole N of the permanent rotor 11. Magnetic flux, as represented by the arrows Al, emerges from the north pole N of the permanent magnet rotor 11, crosses the air gap 1 5 and enters into the teeth 1 4b which serve to concentrate the flux. The flux is directed radially outward through the teeth and into the back iron 1 4c, as represented by the portion A2 of the flux lines. The flux can be seen to divide substantially equally and in opposing directions as shown by flux line portions A3 and A4.

Although not shown for purposes of simplicity, it should be understood that the magnetic flux reenters the magnetic south pole of the permanent magnet rotor 11.

Rotation of the permanent magnet rotor generates an alternating voltage in the stator windings 1 2 to develop a three-phase AC output.

The phase relationship is determined by the physical locations of the output windings 1 2. If desired, the output taken from the stator windings 1 2a through 1 2c may undergo rectification to develop a DC output voltage.

Although the example given is for a threephase machine, the above principles apply to any machines from a single phase type to any number of polyphases less than or greater than the threephase system described.

The voltage generated in the stator windings results from the relative movement between the magnetic flux field developed by the permanent magnet rotor 11 and the stator windings 12 and the magnitude of the generated voltage is proportional to the magnitude of the magnetic flux developed by the permanent magnet rotor 11.

In the event that it is desired to vary the magnitude of the output voltage in the electrical generator of Figure 1 b, no convenient and yet effective means exists for accomplishing this result within the machine prior to the advent of the present invention. This is in contrast to alternators having an electromagnetic field generated by a wound rotor wherein the flux magnitude may be controlled. The flux of a permanent magnet, however, is not readily controllable through straight-forward techniques.

Although means do exist for controlling the flux, such means are much more complicated than the invention to be described hereinbelow.

As another alternative to regulation using the technique of the present invention, power regulators may be provided between the output of the alternator and the load being serviced thereby. However, such power regulators are required to handle full alternator power electronically and are costly and complex devices.

The regulating means of the present invention is simpler in design than any of the means described hereinabove and is also less expensive, more reliable and carries with it several other advantages as will be described more fully hereinbelow.

As mentioned hereinabove, the magnetic field of the permanent magnet rotor 11 enters into the stator iron and is directed through the stator iron portion 1 3c behind slots 1 4a. Although the total flux of the permanent magnet rotor 11 does vary slightly as a function of a rotor position due to the slot openings (note the flux lines in the region of slots 1 4a between teeth 1 4b), the variation is normally small. The total flux developed by the permanent magnet rotor is thus essentially constant.

In alternators of the type described hereinabove, the principal resistance to the flow of flux toward and into the stator iron is the air gap 1 5 since the air gap has significantly higher reluctance (i.e., lower permeability) than the stator iron. For example, the permeability of steel is typically at least 2,000 to 6,000 times greater than the permeability of air. The portions of the magnetic flux path extending through the stator iron between the north and south poles of the permanent magnet rotor 11 encounter much less resistance (i.e., reluctance), even though the path length through the stator iron is longer than the path length of the air gap, due to the much higher permeability of the stator iron. Conversely, it may be said that the reluctance of the air gap is many times greater than the reluctance of the stator iron.For this reason, the air gap between rotor and stator assemblies is selected to be as small as is practical.

The present invention utilizes a technique in which the permeability of portions of the field flux path, preferably in the stator iron, are regulated by means of DC energized control windings provided on the stator iron. Reduction of the stator iron permeability reduces the flux which the stator iron is capable of carrying and thereby reduces the alternator output voltage which provide the basis for precision regulation of the alternator output by controlling the DC current introduced into the control windings.

Figure 2a shows a simplified view of the stator iron 14 upon which are wound a plurality of control windings 16, said windings being wound upon the annular shaped stator iron in a toroidal fashion. It should be understood that the stator iron may be a cylindrical shaped member of any desired axial length. The stator teeth, as shown, provide a convenient means of configuring the control windings 1 6. A DC source (not shown) is connected to the toroidal coils. The DC current developed in the toroidal windings 1 6 in turn creates magnetic flux in the back portion 1 4c of the stator iron 14 which can support only a predetermined amount of magnetic flux before saturation.The more DC flux introduced into the back portion 1 4c of the stator iron, the greater is the resistance (reluctance) to the flux directed to the stator iron from the permanent magnet rotor 11 and hence the lower the induced voltages in the output windings.

The main windings of the electrical generator, in which the output voltages are developed and through which the output currents flow, may be either of the toroidal type or may be of the skein winding type, depending upon the needs of the particular application.

An electrical generator employing the electronic voltage controlling apparatus of the present invention is shown in detail in Figure 2b where the electrical generator 10 is comprised of a permanent magnet rotor 11 having a north (N) and south (S) pole, and a stator assembly having a toroidal shaped member 14 comprising the stator iron, and a pair of toroidal shaped windings 1 2a and 12b.Theends 12a-land 12b-lof windings 1 2a and 1 2b are electrically connected by a common lead 17, which is also connected to one terminal of a load represented by resistance R. Terminals 1 2b-2 and 1 2a-2 are connected in common by lead 18 and are also connected to the opposite terminal of load resistance R.

A pair of control windings 1 6a and 1 6b (represented by dotted lines) are arranged diametrically opposite one another, as are the output windings 1 2a and 1 2b, and are preferably wound closest to the stator iron, the output.

windings 1 2a and 1 2b being wound upon-or over the control windings 1 6a and 1 6b, respectively.

Terminals 1 6a-1 and 1 6b-2 of windings 1 6a and 1 6b are connected to opposite terminals of DC source 19. Terminals 1 6a-2 and 1 6b-1 of control windings 1 6a and 1 6b are connected to one another through common lead 20.

The output windings 1 2a and 1 2b are connected in electrical parallel to deliver current to load resistor R. However, it should be understood that the output windings 1 2a and 1 2b may alternatively be connected in series aiding fashion. The control windings 1 6a and 1 6b are connected in electrical series opposing fashion with respect to any induced voltages so that the resultant voltage which may be induced in one of the control windings is counterbalanced by the voltage which may be induced in the remaining one of the control windings so that the resultant induced voltage is zero. This design assures the fact that no voltage is directed to the DC source 19 from control windings 1 6a, 1 6b.

The current introduced into the control windings 1 6a and 1 6b by the DC source 1 9 causes each of the windings to develop magnetic fluxes H which are additive. The resultant flux tends to drive the stator core 14 either into or toward saturation and thereby limits the amount of induction stimulated by permanent magnet rotor 11. As a result, the output voltage of the electrical generator developed in output windings 1 2a and 1 2b is also reduced.

In order to increase the output voltage of the machine 10, the DC voltage of the control source 1 9 may be reduced thus diminishing the degree of saturation of core 14 which in turn allows the voltage induced in output windings 1 6 to rise by a proportional amount.

The technique for controlled saturation of the field iron (i.e., stator) can also be extended to a family of hybrid generators which are comprised of conventional skein type power windings as an alternative to the aforementioned toroidal control windings. For example, note Figure 2c in which the hybrid electrical generator 10' is shown as being comprised of permanent magnet rotor 11 and field iron 14 having control windings 1 6a and 1 6b and skein type output windings 1 2a' and 1 2b', wherein the circles C1 represent the direction of current flow out from- the plane of Figure 2c through the windings lying along the inner periphery of the field iron 14 and parallel to the axis of rotation RA, and wherein the circles C2 represent the direction of current flow through the associated windings as being into the plane of the Figure 2c.It should be understood that Figure 2c shows one possible arrangement and machines having any other arrangement of output windings may use the technique of the present invention with equal success.

The electrical connections for the control windings of Figure 2c may be the same as those shown in Figure 2b. The alternate design of Figure 2c indicates that the control technique of the present invention may be used in permanent magnet machines of very large output power capabilities and may even be applied, in certain special applications, to generators with standard DC excitation, in which extremely rapid regulation response is desired.

Turning to a consideration of the field iron construction of Figure 2a, it is preferable that a control winding be provided for each slot.

However, as is the case with the embodiments of Figures 2b and 2c, as few as two coils arranged 1 80C apart may be employed. The total number of coils should be equally spaced so that the vector sum of rotor induced voltages is zero. The electrical connections between the coils will then automatically be arranged so that the flux generated by each winding is additive in the back portion 1 4c of the field iron.

When the permanent magnet rotor 11 is rotated, the sum of the voltages induced in the saturation control windings is effectively zero as long as the number of windings is determined in accordance with the manner described above and so long as the coils are uniformly spaced. As a result, no resultant voltage is developed by the control windings. Experiments indicate that adequate DC control may be obtained through the use of a low level DC source which is an important design advantage and results in the fact that power and control circuits are electrically isolated from one another within the generator.

Figures 3a and 3b show one manner in which a novel flux control means of the present invention may be utilized to regulate the DC voltage output of an alternator-rectifier combination. As shown in Figure 3a, the three-phase electrical generator is comprised of output windings 1 2a through 1 2c connected in wye-fashion, with one of their end terminals connected in common at 22, and with the remaining terminals each connected in common to a pair of diodes 23, 24 and 25. The diode pairs are comprised of first and second diodes, for example diodes 23a and 23b, connected with their polarities opposing. Diodes 23a, 24a and 25a are connected to common terminal 26 while diodes 23b, 24b and 25b are connected in common to terminal 27. The load resistor R1 is connected across common terminals 26 and 27.

Figure 3b shows the three-phase alternator 10 of Figure 3a in simplified fashion wherein load resistor RL is connected across the output terminals 26 and 27 of the full wave rectifier circuit incorporated in alternator 1 0.

A portion of DC voltage developed across load resistor RL is coupled to a summing circuit comprised of resistors R a and Rb. The output of the summing circuit is coupled to the input of amplifier 28 whose output applies a control current ic to the control windings 1 6a-1 6c of alternator 10 for voltage regulation, as will be more fully described. It should be understood that control windings 1 6a-1 6c are winding pairs electrically arranged in the manner described hereinabove.

The DC voltage developed across load resistor RL is compared with the reference standard voltage applied to input 29 of summing resistor Rb, a technique typically employed in regulated power supplies. Since this is a well-known technique, Figure 3b shows a simplified manner for implementaion of this capability, and it should be understood that any electrical circuit having this capability may be employed for achieving voltage regulation of the type described.

The output of the comparison circuit, which is comprised of the summing resistors Ra and Rb and amplifier 28, is a measure of the differences between the desired output voltage and the actual output voltage. The differences between -the voltage levels applies to the summing circuit result in a corresponding change in the control current 1c delivered to the control coils, thereby providing the desired regulation. The output voltage delivered to load RL may thus be maintained at a constant level through the use of this technique.

The control technique of the present invention may also be employed to operate as a voltage limiter or circuit protection means in which a control current is generated only when the output voltage developed by the electrical generator exceeds a predetermined level.

Considering Figure 3c a current sensing impedance element, which may, for example, be a resistor 30 of very low ohmic value is connected in electrical series between generator 10 and load resistor R,. (Alternatively, when regulating AC, the current sensing element may be a transformer having an input winding in series with the load R, and an output winding coupled to the control circuit). The voltage across resistor 30 is a measure of Inad current 1,. The major portion of the output voltage of generator 10 is developed across load resistor RL One terminal of resistor 30 is coupled to current sensing DC amplifier 31 which amplifies the voltage developed across resistor 30, and applies the amplified output to one terminal of Zener diode 32.The opposite terminal of Zener diode 32 is coupled to ground (or a reference potential) through resistor R,. The common terminal 33 between Zener diode 32 and resistor R, is connected through conductor 34 and resistor R4 to one input of control amplifier 35.

Depending, of course, upon the rating of Zener diode 32, so long as the breakdown voltage of Zener diode 32 is not exceeded, Zener diode 32 remains nonconductive. Thus, no control current is fed back to control amplifier 35 through conductor 34 and resistor R4, and thus Zener diode 32 effectively blocks the control amplifier 35 from producing an output so that no control current 1G is provided for the control windings 1 6 (see Figure 3a).

In the event that the voltage of the load as represented by resistor RL rises too high or drops too low the regulating means of Figure 3b apply.

If the load resistor is accidentally short-circuited, the voltage across current sensing resistor 30 increases instantaneously with the increase in current through load resistor RL As soon as the voltage across current sensing resistor 30, after amplification, exceeds the breakdown voltage of Zener diode 32, Zener diode 32 will conduct thereby applying a feedback current to control amplifier 35 which in,turn develops a control current applied to the control windings 1 6. The control current developed by control amplifier 35 is adapted to saturate the field iron which abruptly reduces the output current of the electrical generator developed by output windings 1 2 to prevent the de-magnetization of the permanent magnet member 11.It should be noted that the techniques described in connection with Figures 3b and 3c may be combined as represented for example by the dotted line connection between one terminal of resistor RL and an associated input of control amplifier 35 through resistor R6.

The techniques described hereinabove may also be applied for objectives other than output voltage regulation. For example, the techniques of the present invention may be employed in DC motors having a wound rotor arrangement as shown in simplified fashion in Figure 2d. The motor 40, only portions of which have been shown in Figure 2d for purposes of simplicity, is comprised of a permanent magnet stator 41 which may, for example, have a north and a south pole arranged at 1 800 intervals. Figure 2d shows the north pole N of the permanent magnet stator.

The rotor is comprised of a substantially annular shaped ferromagnetic member 42 which will hereinafter be referred to as the armature iron.

The armature iron 42 is provided with a plurality of identical slots 42a. Adjacent slots 42a cooperatively define the teeth 42b of the armature iron. The armature windings, for example, armature windings 1 2a and 12b, are shown as being wound about selected ones of said teeth 42b.

In the embodiment of Figure 2d, the control windings 1 6 are shown as being wound about the back iron portion 42c of the armature iron 42 which comprises the inner periphery thereof.

Preferably each slot 42a is provided with a control winding 1 6.

Slip ring assemblies must be provided for coupling the DC control current to the control windings. Conventional commutator means may be provided for the armature coils. The.slip rings and cooperating brushes are conventional and have been omitted from Figure 2d for purposes of simplicity. A typical design is shown, for example, in Figure 3-37, page 140 of the text Electrical Machinery, Copyright 1952 by McGraw-Hill.

The DC motor design of Figure 2d may. be modified in a simple manner to function as a DC generator by mechanically driving the rotor and deriving an electrical output from windings 12.

The disadvantage of the arrangement of Figure 2d resides in the fact that the additional complexity of the slip ring arrangements is required thus limiting the areas of application of this alternative embodiment.

The control techniques of the present invention may also be employed in DC tachometers which have substantially the same configuration as shown in Figure 2d wherein the saturation control technique is employed as a method of voltage gradient control, i.e., wherein the voltage gradient varies as a function of speed.

In summary, it can be seen from the foregoing description that the present invention provides a simple and practical technique for regulating the total magnetic flux in an electrical machine by means of DC saturation of portions of the iron paths of the field iron through which said flux is concentrated. DC saturation is obtained through the use of electrically isolated DC control windings which require significantly less power than that developed by the electrical machine being so regulated. Also, the higher the permeability of the field iron in the absence of the control current, the less DC control power is required for saturation of the field iron.

The regulation obtained through the technique of the present invention is extremely rapid since it reduces the lux rise time caused by the L/R time constant present in conventional generators equipped with "forward action" regulators as opposed to the "reverse regulation" technique employed by the present invention. The name "reverse regulation" derives from the fact that converse to the standard regulation function, a rise in machine termainal voltage results in a proportionate decrease in control current, hence the term "reverse regulation".

Measurements of AC generating apparatus designed in accordance with the principles of the present invention indicate that voltage transients can be stabilized within one quarter to one half cycle from the time of an event. In DC generating apparatus the load transient condition is stabilized in a time period limited only by the characteristics of the load circuit and the generator steel.

Claims (12)

Claims

1. A machine comprising a rotor assembly, a cooperating stator assembly, said rotor assembly and stator assembly being rotatable relative to each other, one of said rotor and stator assemblies comprising means for generating a magnetic field directed toward the other one of said assemblies, the remaining one of said rotor and stator assemblies comprising a member made of a material having a non-linear permeability, first winding means on said member for generating an electrical output responsive to the movement of said magnetic field past said first winding means due to the relative rotation between said rotor and stator assemblies, and control means including DC power means and control winding means on said member responsive to said DC power means for introducing magnetic flux of a predetermined magnitude in said member te alter the level of the output developed by said output winding means.

2. A machine according to Claim 1, wherein said member is an annularly shaped member.

3. A machine according to Claim 1 or 2, wherein said control winding means is adapted to prevent the moving magnetic field provided by relative rotation between said rotor and said stator assemblies from developing any resultant output due to the presence of said control winding means.

4. A machine according to Claim 1,2 or 3, wherein said annularly shaped member is provided with a plurality of radially aligned slots extending into said annularly shaped member from the inner periphery of said annularly shaped member, said first winding means are arranged in at least some of said slots, and said control winding means are arranged in at least some of said slots.

5. A machine according to any one of the preceding claims, wherein the flux generated by said control winding means is aligned transverse to the flux generated by said first winding means.

6. A machine according to any one of the preceding claims, further comprising load means for receiving the output developed by said first winding means, a DC reference source, summing means for summing the output developed by said load means and said DC reference source, and amplifying means for applying the output of said summing means to said control winding means.

7. A machine according to Claim 6, further comprising coupling means coupled between said summing means and said first winding means, and circuit means for applying a signal to said summing means for increasing the field produced by said control winding means in the event of an increase in the output current of said machine abouve a predetermined safe threshold.

8. A machine according to Claim 7, wherein said circuit means comprises a voltage sensing element.

9. A machine according to any one of the preceding claims, wherein said stator comprises sdid member.

10. A machine according to any one of the preceding claims, wherein said control winding means includes control windings and said first winding means includes first windings, and said control windings and said first windings overlap to at least some extent.

11. A machine substantially as described and shown in the accompanying drawings.

12. A method of regulating the output voltage from an electrical generator by regulating the total magnetic flux in the generator by means of d.c. saturation of portions of the iron paths of the field iron through which said flux is concentrated.