GB2114819A

GB2114819A - Single phase alternator

Info

Publication number: GB2114819A
Application number: GB08302159A
Authority: GB
Inventors: Jean Pierre Fauvet
Original assignee: Mase Electromeccanica SpA
Current assignee: Mase Electromeccanica SpA
Priority date: 1982-02-16
Filing date: 1983-01-26
Publication date: 1983-08-24
Also published as: IT1157431B; GB8302159D0; DE3304664A1; IT8203338A0

Abstract

The alternator is of the type with a rotating armature and a stator, the former being devoid of damper windings and the terminals 5a-5b of the excitation coil 4 being connected to a diode 6. The conductors 8 of the windings of the stator 11 are so connected as to define two separate coils 12-13, namely an auxiliary coil and a main coil, these being perpendicular one to the other. The terminals of the auxiliary coil 12 are connected to a capacitive load 14 of a value such as to create in the coil 12 a leading current Ic with respect to the induced voltage, while to the terminals 15a-15b of the main coil 13 are connected the utilizers 15. The alternator is self-starting, self voltage regulating, withstands considerable overloads and has optimum electrical characteristics. <IMAGE>

Description

SPECIFICATION An improved single phase alternator The invention relates to an improved single phase alternator.

As is known, the synchronous generator (also referred to as an alternator) is habitually constructed with a rotating armature and with a stator. Since the armature is direct current excited, it is necessary to have a direct current source of energy (dynamo or group of rectifiers, etcetera) with which to supply it.

In cases when the direct current source is constituted by at least one dynamo that is independent of the armature or is mounted on the shaft of this, it is necessary to provide, on the shaft of the armature, two rings connected to the said source by means of sliding brushes: in this way the excitation coils of the armature are supplied with direct current.

When, instead, the direct current source of energy is constituted by a bank of rectifiers placed externally to the machine (and therefore fixed), the aforementioned rings and brushes need perforce to be provided in order to supply the direct current to the armature of the alternator.

A constructional method is also known that requires neither rings nor brushes since provision is made for a number of rectifiers to be mounted on the shaft of the armature (therefore rotating with this) that is supplied with direct current by a synchronous generator of the fixed armature, brushless type (carried in rotation by the shaft of the said armature).

Various problems arise with the technical solutions outlined above, derived from the fact that the slip rings oxidize, the brushes spark and wear, and it is necessary to provide appropriate sources of energy (varying between 0.3% and 1.5% of the rated power of the alternator connected) constituted either by rectifiers, one or more dynamos, or by brushless type alternators.

It is also known that the load voltage at the terminals of the alternator differs from the no-load voltage, this due principally to the voltage drops that occur internally in the alternator (on the resistance and the reactance of the alternator), and due to the feedback of the stator currents, the magnetic field of which exerts, for an ohmicinductive load (normally applicable in the case of utilizer loads), a demagnetizing action on the magnetic field created by the armature.

The above excitation systems do not ensure the regulation of the voltage at the terminals of the alternator (which must be maintained, with respect to a nominal value, within a predetermined variation range), and thus it is necessary to have voltage regulation groups (that operate to vary the excitation current of the coils of the armature of the alternator) which, compatibly with the system of excitation employed can be of what is known as the shunt, compound or the shunt and series type, or be constituted by an electronic regulator. The said regulation groups cause constructional complications (in addition to the manufacturing features and peculiarities of the excitation systems listed) and require additional electrical circuits, which is to the disadvantage of the efficiency of the alternator and has a notable negative effect on the overall cost of the said alternator.

Another constructional feature of known alternators lies in the fact that the armature has by necessity to be provided with a damper winding (Leblanc cage) whose function is to shield the excitation coils against the influence of spurious rotating fields (rotating in the reverse direction to that of the main rotating field) that originate in three phase alternators in the presence of unbalanced loads, or against the rotating field that is inverse and originate in a single phase alternator.

The object of the invention is to furnish a single phase alternator, of the type with a rotating armature and a stator, whose conformation is such as not to require either the damper winding or a direct current source of energy for its excitation, and also to be self-starting and self voltage regulating as the load increases, even for highly inductive loads.

A further object is to furnish an alternator that, in addition to fulfilling the preceding object, is able to offer better efficiency, a lower temperature-rise and a considerably lesser cost in general compared with the efficiency, the temperature-rise and the cost of known single single phase alternators of naturally the same rating.

The above objects are achieved with the improved single phase alternator of the type with a rotating armature and with a stator, according to the invention, characterized by the fact that in the armature the magnetic circuit is constituted by laminations made of ferromagnetic material, insulated one with respect to the other, side by side in pack form and locked to the shaft of the said armature in directions radial with respect to the said shaft, and the terminals of the excitation circuit are connected to a unidirectional conduction element defining a pre-established direction in the said circuit for the excitation current, and characterized by the fact that the conductors placed in the slots or the stator define two coils, the axes of which are angled one with respect to the other, the terminals of one coil being connected to a capacitive load, while the terminals of the other coil can be connected to the utilizers of the said alternator.

The reactance of the said capacitive load is greater than the overall synchronous reactance of the coil in respect of the said capacitive load.

The axes of the said coils are perpendicular one to the other or tend as much as possible towards the said particular position, compatibly with the coil mounting difficulties.

The said unidirectional conduction element is constituted by a solid state diode.

The characteristics of the invention are given emphasis in the text that follows with reference to the accompanying table of drawings, in which: Figure 1 is a diagrammatic view of the alternator forming the subject of the invention; Figure 2 is the wiring diagram for the alternator in question; Figure 3 is a table of the most significant parameters for the said alternator compared with similar parameters for some other known types of single phase alternators.

With reference to the said figures, at 1 is shown the shaft of the armature 2 of the alternator in question 10, the drive of which at constant speed (of value n=60 f/p, where n is the number of revolutions per minute, fis the frequency of the induced voltage and p is the pairs of poles of the armature 2) is achieved in a known fashion by means of a non-illustrated prime mover.

The magnetic circuit of the armature (in the case illustrated, of the salient pole type with two poles, thus p=1) is constituted by laminations 3 (so shaped as to define the poles N and S and the pole shoes 3a and 3b) made of ferromagnetic material, insulated one with respect to the other, and placed side by side in pack form in directions radial with respect to the shaft 1. The items for locking the laminations 3 to the shaft 1 have not been illustrated since they are known.

The excitation circuit of the armature is (in the case described) constituted by two coils 4 in series. The connection of the said coils is, as is known, such as to give rise to ampere-turns in the same direction.

Access to the coils 4 can be gained from the outside by means of the relevant terminals 5a (positive) and 5b (negative). At the time of construction of the alternator, the armature is magnetized (for example by sending a positive current pulse from terminal 5a to terminal 5b) in such a way that the residual induction be such as to define the North pole N and the South pole S therein.

Between the terminals 5a and 5b is connected a diode 6, the anode of which is connected to the terminal 5a (to the said diode can be connected, in parallel, a suitable capacitor 7 for protection against eventual surge voltages). The particular connection of the diode 6 makes it possible for a current I directed in the course taken by the conduction directed by the said diode, to circulate. The direction of the said current is such as to create in the armature a field of magnetic induction in the same direction as the existing residual induction.

It should be stressed, since this is extremely advantageous, that the armature 2 is not provided with damper windings and that the coils 4 are not connected to any source of direct current energy.

The conductors 8 placed in the slots 9 of the stator 11 are connected (in accordance with known techniques) in such a way as to define two coils 12 and 13, the axes of which are perpendicular one to the other, or are as perpendicular as possible. In the case illustrated in Figure 1, there are twenty four slots, eight of which for the coil 12 and the remainder for the coil 13.

The load on the coil 12 (or auxiliary coil) is constituted by a capacitor 14 (of a few yF). The capacitive reactance of the said capacitor is greater than the synchronous reactance of the coil 12 and thus the load on the coil 12 "seen" is of the ohmic-capacitive type.

The terminals 1 5a of the other coil 13 are destined to be connected to the utilizers 1 5 of the alternator A description will now be given of the operation of the alternator, with it being assumed that initially there is no load on the alternator (with the terminals 1 spa open).

Just as soon as the armature is carried in rotation at velocity V (for example, in the direction N) the residual induction of the armature creates a weak flux that "hits" at velocity V the conductors of the coils 12 and 13 and induces in them a voltage of a few volts.

The voltage induced in the conductors of the coil 1 2 causes the circulation therein of a consequent current 12 (since the load on the coil 12 is constituted by the capacitor 14). The current 12 creates a magnetic field that can be thought to be constituted by two counter-rotating magnetic fields, namely one direct and one inverse, of identical amplitude. The direct field (the velocity of which corresponds to velocity V of the armature) exercises a magnetizing action on the flux produced by the armature since the load on coil 12 is of the ohmic-capacitive type. The inverse field rotates in the opposite direction to that in which the armature itself revolves, and thus "hits" the conductors of the coils 4 at a velocity 2V.

From the foregoing, it follows that of the voltage induced in the conductors of the coils 4, only the half wave that directly polarizes the diode 6 produces the previously mentioned current I.

The said current I (of the pulsating type) strengthens the flux produced by the armature, and this intensifies, in succession, the phenomena to which reference above has been made.

When operating at the rated value, the velocity V of the armature is such as to satisfy what is well known (and has been previously stated), namely that n=60 f/p, the voltage induced in the coil 12 (and consequently the voltage at the terminals of the capacitor 14) is limited by the saturation of the overall magnetic circuit (stator and armature) of the alternator, and the voltage induced in the coils 4 by the inverse field is of 2f frequency.

It is obvious that in the condition specified above, that is to say at no-load, the resulting flux (due to the armature and to the feedback of the stator currents caused by the direct rotating field) induces a determinate voltage at the terminals of the coil 13.

From what has been said above ensues the extremely advantageous fact that because of the auxiliary coil 12 and the diode 6, the alternator is self-starting and self-exciting.

Once the terminals 1 5a are connected to the utilizers 15, a load current 1c passes through the coil 13 and produces a magnetic field that can be considered to be constituted (as is known) by a direct field and an inverse field.

The voltage at the terminals of the utilizers 1 5 should tend to decrease for two reasons, namely the drop on the internal impedance of the coil (impedance of the ohmic-inductive type) and the feedback of the stator currents of the direct component of the field, caused by Ict this feedback being de-magnetizing since the load 1 5 is generally of the ohmic-inductive type.

With the improved alternator according to the invention, the above mentioned tendency to decrease is offset and practically rendered nil: in other words, the voltage variations at the terminals 1 spa between no-load and load are maintained at a smail percentage (for example: =3%). The inverse field (proportional to lc) does, in fact, induce in the coils 4 a voltage (at 100 Hz if f=50 Hz), the maximum value of which is proportional to l; consequently this causes an increase in I and a consequent increase in the magnetic field created by the armature; the said field increase brings about an increase in the total flux of the alternator which results in an increase in the voltage induced at the terminals of the coil 13.

The increase in the voltage induced at the terminals of the coil 1 3 tends to get larger (as 1c increases) also on account of the fact that the increase in the flux of the alternator also brings about an increase in the voltage at the terminals of the coil 12 which causes an increase in I whose magnetic field exercises a magnetizing action on the flux of the alternator.

From the foregoing, it follows that the alternator according to the invention regulates by itself its voltage, even in the presence of highly inductive loads 1 5.

The voltage at the terminals 1 5a is kept, percentage-wise, within values acceptable even in the presence of considerable overloads (of 100% for example) for the reasons already outlined. An increase in IC, in fact, causes an increase in the field produced by the armature with all the consequences derived from this increase.

The efficiency of the alternator is greater than that of the alternators known, obviously of the same rating. Indeed, the excitation circuit losses are, in this particular alternator, notably reduced in comparison with similar losses in the alternators known, since there are no brushes, slip rings or direct current supply sources.

It has been seen from laboratory experience that the temperature-rise reached at the rating by the conductors of the main coil (namely coil 13) is considerably below the temperature-rises in the stator conductors of the alternators known (that employ a great variety of groups for regulating the voltage), naturally of the same rating.

By way of an example, the table in Figure 3 shows the most significant parameters in respect of certain known types of alternators compared with the self same parameters relevant to the alternator described herein.

The said table is in five lines that refer (see column 1) to alternators listed as A, B, C, D and E, respectively. The one mentioned last is the alternator described herein. The first four are provided with shunt type regulation, compound type regulation, shunt and series regulation and electronic regulation, respectively. The parameters considered for comparison purposes are: (Column 2) the temperature-rise at the rating by the stator conductors at 1c rated current; (Column 3) the voltage variation percentage between no-load and load; (Column 4) the efficiency at 75% load with cos 4 > =1; (Column 5) the overload percentage with respect to the 1c rated current; (Column 6) the unit cost, with that of the alternator describd herein being, for comparison purposes, listed as being =1.

To conclude, the alternator described herein does not have damper windings nor does it require a source of direct current for supplying the excitation circuit of the armature (therefore it has no need for brushes, slip rings, banks of rectifiers or auxiliary generators, etcetera). It is self-starting, self voltage regulating as the load increases (even when the load is highly watless), it withstands considerable overloads and, compared with the alternators known of the same rating, it has a greater efficiency, a lower temperature-rise and cost-wise is particularly interesting. The lack both of the regulating group and the direct current supply source makes it possible to limit the axial projection of the alternator.

The extreme constructional simplicity of the alternator has a positive effect both on the reliability and maintenance requirements of the alternator.

It is understood that the foregoing description has been given purely as an unlimited example, and thus eventual variants of a practical nature to the constructional details (for example, the armature can be of the smooth pole type) are understood to all fall within the framework of the invention, as claimed hereinafter.

Claims

1. An improved single phase alternator of the type with a rotating armature and a stator, characterized by the fact that in the armature the magnetic circuit is constituted by laminations made of ferromagnetic material, insulated one with respect to the other, side by side in pack form and locked to the shaft of the said armature in directions radial with respect to the said shaft, and the terminals of the excitation circuit are connected to a unidirectional conduction element defining a pre-established direction in the said circuit for the excitation current, and characterized by the fact that the conductors placed in the slots of the stator define two coils, the axes of which are angled one with respect to the other, the terminals of one coil being connected to a capacitive load, while the terminals of the other coil can be connected to the utilizers of the said alternator.

2. An alternator according to Claim 1, wherein the reactance of the said capacitive load is greater than the overall synchronous reactance of the coil in respect of the said capacitive load.

3. An alternator according to Claim 1, wherein the axes of the said coils are perpendicular one to the other.

4. An alternator according to Claim 1 , wherein the said unidirectional conduction elements is constituted by at least one solid state diode.

5. An alternator substantially as hereinbefore described with reference to the accompanying drawings.