US1509501A - Apparatus for exciting alternators - Google Patents

Description

Se t. 23 1924.

p A. BLONDEL APPARATUS FOR EXCITING AI'JTFIRNA'IORS Filed Feb. 28. 1920 3 Sheets-Sheet 1 Fig. 4

villi/Ill 0 A. BLONDEL.

APPARATUS FOR EXCITING ALTERNATORS Sept. 23 1924- Filed Feb. 28 1920 3 Sheets-Shoot wwM 2 7 4 Sept. 23, 1924. 1,509,501

A. BLONDEL APPARATUS FOR .lXCITliyG ALTERNATORS Filed Feb. 28. 1920 3 Sheets-Sheet 5 A rra/m i-rsl Patented Sept. 23, 1924.

UNITED STATES ANDRE BLONDEL, OF PARIS, FRANCE.

APPARATUS FOR EXCITING ALTERNATORS.

Application filed February 28, 1920. Serial No. 361,978.

To all whom it may concern:

Be it known that I, Arman BLONDEL, of 41 Avenue de La Bourdonnais, Paris, France, engineer, have invented new and useful-Improvements in Apparatus for Exciting Alternators, which apparatus is fully set forth in the following specification.

This invention relates to means for exciting alternators which work either as generators or receivers (synchronous motors) the object being to reduce the amplitude of the oscillations to which they are subjected if coupled and the miximum current which they first deliver when accidentally shortcircuited.

It is known that the armature reaction of alternating current generators produces a lowering of voltage at the brushes, when the machine works, this voltage drop being due to the wattless current-component.

Many authors. amongst which can be cited Rice, Blondel, Boucherot, Le Blane, Danielson, Lunt, Iiatour, Johnston, Siemens & Halske, have previously proposed excitation-methods by which this effect may be annulled, by a compensation of the armature reaction obtained by different ways, and

particularly by the use, as exciter, of a rotating converter, fed by a current furnished by transformers mounted in series or in shunt. This excitation means is well known, but the compensation of the armature reaction is objectionable for it increases the current intensity when a short circuit takes place; and increases the reactions of the coupled alternators.

I have discovered that in order to facilitate the parallel running of two or more alternators, for the feeding of a net, these alternators being actuated by reciprocating engines, it is advisable to reinforce as much as possible the armature reaction by the effect of the wattless current which run between machines.

My process is intended to be applied to alternators, the voltage of which is regulated by the variation of resistances inserted in the field windings. This resistance variation may be controlled automatically by known systems as those of Tirrill, Thury, Brown-Bovery. etc. In carrying out this process it is aimed to aggravate the armature reaction of an alternator without detracting from its voltage regulation, and with the aim to reduce the wattless currents exchanged by the transformers when they work in parallel, and also to slow down and damp the local oscillations of the alternatorsQ Experience shows that the oscillations of alternators coupled singly or in parallel to the line and working as generators can be reduced by varying the inducing field in accordance with the variation of the direct reaction flux of the armature through the field circuits.

' On the other hand experience has shown that on the sudden short-circuiting of an alternator the demagnetization of the field magnets under theeifect of the direct reaction of the armature is retarded by the current induced in an unfavorable direction which this reaction generates in the exciting circuit. This unfavorable effect would evidently be reduced if at the same moment the variation of the current is made to cause an electromotive force of opposite sign to that which produces the diminution of flux by the induced field of flux traversing the primary circuit to act in the exciting circuit.

In both cases it will be seen therefore that it is desirable whenever the direct reaction of the armature causes a diminution of the flux of the field magnets to bring about an instantaneous diminution of the electromotive force applied at the terminals of the exciting winding of the field magnets, for this will cause a reduction of the current which normally passes from the exciter or from the exciter lbars of the central station to the field magnets of the alternator.

The present invention consists in the addition to any exciting alternator of an arrangement for exciting which produces such instantaneous reduction of the electromotive force proportionally to the variation of the armature counter-ampere-turns opposed to the field magnets, in combination or otherwise with other processes for automatic relatively slow regulation of the field excitation which allow the diiference of the potential at the terminals of the alternators or at a suitable point of distribution in the line fed by this alternator to be maintained constant between appropriate limits.

It will be well to explain here that numerous processes are known for such automatic regulation of the tension of an alternator excited by an exciter of ordinary type.

In particular there may be cited the automatic regulators of Thury and of Tirrill as characteristic types of apparatus for obtain I ing the object desired by difierent means.

Thurys process consists in the automatically actuated-rheostat controlled by a simple or compensating voltmeter (compensated by thecurr'ent in such a manner as to take into account the loss of line tension); so soon as the tension of distribution falls below the fixed value, the handle of the rheostat comes automatically into action in such manner as to lessen the resistance of the excitmg circuit of thealternator until the tension has regained its normal value; the rheostat is operated in inverse directlon if the tension rises above the desired value. v

In the Tirrill process the same result is obtained by means of a trcmbler or of a contact which short-circuits and introduces a resistance mounted in series in the exciting circuit; the ratio of the durations of closing to the durations of opening being modified to obtain a larger or smaller exciting current. This ratio is also constantly regulated by an electro-magnet placed under the control of the tension of distribution.

These regulating apparatus or any other analogous apparatus may be interpolated, for example, in one of the exciting circuits of the exciter which delivers current to the circuit of the field magnets of the alternator.

According to the present invention, an exciter of the ordinary type of alternators 1s modified by providing it with a counter-compounding arrangement, that is to say an arrangement which produces the inverse effect to that which is instantaneously produced in compound exciters by the action of the current delivered by the alternator. The most simple method of obtaining this result in the general case of a polyphase alternator having any desired number of phases, consists, for instance, in interpolating in each of the conductors passing from the alternator, the primary of a series-transformer analogous to those employed for compounding alternators and in causing the secondary circuits of each of these transformers to act in the opposite direction to that which would be required to produce the compounding (that is regulation of the tension).

In the accompanying drawing:

Figs. 1 to 5 illustrate diagrammatically some methods of carrying out the invention.

Fig. 6 shows the rheostats of a Thury regulator.

A is the armature of the alternator (for the sake of clearness, it is supposed to be a monophase alternator); M is the inducing circuit; f, f, are wires leading from the alternator and corresponding to one of the phases; B, B are the alternating current us bars of the central station generator or a portion of the central station; f, f, are

wires leading to a second alternator coupled in parallel with the alternator A; B B are collectin bars located at some other point from WhlCh pass the feeders at the outlet of verter (or the dynamo in Fig. 4), of a suitable type; J, J its field magnet; 12, b, b, b, are the rings of the ordinary winding of the armature or of a winding superimposed on the same armature of the rotary converter E,; E is a rotary-converter or a dynamo; J J, are its field magnets; 5 b the rings ofthe converter E alternating current side; C, C are a pair of two direction contacts; N is a battery of accumulators.

D is a counter-compounding series transformer: D a transformer connected in parallel with the wires f, f, of the alternator or with a group B, 13,; D. is an exciting transformer whose primary is in series with the exciting circuit of the alternator and whose secondary feeds a special circuit placed on the field magnets on the exciter E, (or of the exciter E in Fig. 3); R, R R R are exciting rheostats; S is a reactor, T, T are automatic excitation regulators: of course only one of these automatic regulators is provided for each alternator or for each group of alternators working in parallel ;'the diagram shows two examples of the arrangement. K, K are switches which serve to cut out the unused regulator; P is a tension limiting arrangement or discharger of a known type seen in Fig. 3 only, but which may be introduced in any other arrangement. I is a circuit breaking switch controlled by windings m, or m, and by the transformer D; it breaks the exciting circuit in the case of an undue output from the alternator: it may be provided in any of the arrangements.

Fig. 1 shows an arrangement which may be adopted when each alternator at a generating station is provided with a countercompounding exciter fed on the alternating current side with current resulting from two transformers, series and parallel.

Fig. 2 shows the employment of a similar counter-compounding rotary converter but having two alternative windings fed respectively from two separate circuits, one derived from a series transformer, the other from a transformer fed in derivation.

Fig. 3 corresponds to the case in which the counter-compound exciter whose armature receives alternating current from a countercompounding transformer is itself excited of bus bars B, B or. v

partly in shunt (or in series) partly from an independent excitation which may be derived from a battery of accumulators, a dynamo or a rotary converter.

F r instance, the compounding effect is pr need by a dynamo E of any type whose armature is in the excitin circuit of the alternator and whose field is fed from any source as for example from dynamo E This dynamo E is thus excited from an in dependent circuit and the rings b 6 of its armature are connected to the transformer in series with the circuit of the alternator in such a manner as to produce a magnetic eflect opposite to the field produced by the independent exciter circuit.

Figs. 4 and 5 showspecial exciting windings which augment the apparent self-induction of the field circuits and which may respectively be adapted to the arrangement shown in Figs. 1, 2 and 3.

In all these figures, the circuit of the alternator is supposed to be monophase for the sake of clearness, but usually the alternator will be provided with any desired number of phases and poles. In the same way, the counter-compound transformer may have any number of phases and feed a corresponding number of phases of any of the rotary converters shown.

When the transformer D is common to several alternators working in parallel, its secondary is connected to the exciting bars B, B from which the Wires which feed respectively each of the exciters E on the alternating side lead to the rings 6 b in the case of Fig. 1, to the rings 6 b in the case of Fig. 2, and to the rings 6 b (Fi 3) for a rotary converter E of any type wliich may be provided for the purpose of producing a continuous independent excitation of the exciter E There exist three main types of known arrangements of compounding converters; a first which utilizes for its alternate cur rent feeding of the armature the tension derived from the transformer D and from the transformer D (Fig. 1). The compounding windings may be distinct from the winding which delivers continuous current (Leblanc type for example). A second which receives in two separate windings on the armature, currents produced respectively by the two electromotive components of the transformers D. and D Fig. 2. A third which only utilizes on the alternating side-current produced by the tension of the series transformer (Fig. 3).

According to this invention one or other of these arrangements is modified by inverting the direction of the connections of the secondary of the series transformer with respect to the rings 6, 6 The degree of counter-compounding may be regulated varying the electromotive force produced in the secondary of the series transformer; this may be effected by varying the ratio of transformation in any of the well known wags.

f course, all phases should be regulated in the same manner; one phase only ,is shown in order to simplify the figures.

The position of the armature of the exciter or rotary converter E on the shaft of the alternator with which it is fast is regulated in such a manner that the field produced' by the compounding currents (that is to say by the currents which are in phase opposite to those of the primaries of the series transformer) is in direct opposition with the normal inducing field of the exciter; this therefore acts as counter-compounding.

The continuous excitation of the exciter E may be effected in series or in shunt (but preferably in shunt in the arrangements shown in Figs. 1, 2 and 3) by the circuit passing from the brushes of the commutator.

The exciter may be stabilized by providing it with a continuous supplementary excitation through an independent circuit. This independent excitation may be derived for example from an exciter E arranged in each alternator; but usually it would be common to a portion or to the assemblage of the station alternators working in parallel.

This allows the exciter E to be actuated by a shaft independent of that of the alternator; it may be driven by an asynchronous or synchronous motor or may itself be a rotary converter receiving alternating current derived from a transformer in shunt as shown in Figs. 3 and 4: in this latter case only it is provided with rings 6 and b In all the preceding arrangements there may be provided another partial excitation of the exciter E caused by variable currents generated in the exciting circuit of the field magnets of the alternator during the oscillations of this latter or when a sudden overcharge (flow of current) occurs. This exciting winding is shown diagrammatically in Figs. 5 and 6 in which it is shown alone in order to simplify the diagrams; it may however be superposed on the other field magnet windings or may replace one of them. The exciter thus counter-compounds itself but only for variation in speed of the alternator which it excites because the induced currents have the frequency of the hunting oscillations of the armature of the alternator about the mean speed. finally this winding produces for its frequency the same effect as that of a self-induction interpolated in the circuit of the field magnets. Of course a resistance is introduced into this inducing circuit sufficient to enable the current produced to be'substantially in phase with the electromotive force induced in the secondary of the transformer D,.. This secondary may feed the exciting circuit of E in place of E when there is an exclter E the effect produced remains of the same na ture.

Alternators thus compounded may also advantageously be employed to reduce the effects of shortcircuiting; directly a shortcircuit in the line or in the Wires connecting the alternators to the bars takes place, the counter-compounding series transformer D delivers an intense demagnetizing current into the armature of the exciter whose tension will be reduced. This effect is again increased by the influence of the excitation in shunt. The exciter will thusaid in the demagnetization of the field magnets which tends to cause the armature reaction of the alternator but which is hindered when there is no counter-compounding and this will take place mainly at the commencement of the short-circuit by the sudden increase of current in the field magnets,-the well known phenomenon discovered by Dr. Punga.

The presence of a reactor S reduces such afliux of current and favors the fall of tension at the brushes of the exciter.

Counter-compounding allows alternators to be more economically constructed as the gap may be reduced and therefore the ampere-turns on its field magnets.

It may be objected that this arrangement increases to a greater or less extent the variations in voltage in function of the load above all when the current produced by the alternator is wattless. Inorder to compensate for this increase of variation there may be added to the arrangement a tension regulator of one of the lfiiown types (see what has been stated above) this regulator has its main circuit interpolated in series either in the excitation circuit of the exciter E1, or in the excitation circuit of the exciter 133 In both cases, the effect of the, automatic regulater is progressively to modify the tension at the terminals of the field magnets of the alternator in such a manner as to re-establish the desired tension of distribution in spite of the contrary effect of the countercompounding exciter. In order to avoid in the case of a short-circuit the automatic regulator counterbalancing excessively the effect, of the counter-compounding cxciter, such automatic regulator is regulated in such a manner that in norm-a1 working it can only deliver to the alternator an exciting current not greater than that which the largest output requires; there may even be added to the automatic regulator a working terminal which cuts out its circuit or which interpolates in its circuit a very large supplementary resistance as shown at B in Figs. 4 and 5 in which the rheostat of a Thury regulator is shown diagrammatically so that after having increased the excitation to a very high value the automatic regulator continuing its action suddenly reduces the excitation to a mimmumvalue.

When these automatic regulators are 'placed in the position T Figs. 1 to 3, it may also be desirable that they should have a sufliciently slow action orevenbe retarded by some arrangement in order to prevent their action from being felt during the duproviding a counter-compounding action in such manner that an instantaneous increase of the series watt current exchanged between the alternators causes an instantaneous diminution of the field current and automatic slow-acting means for compensating for disturbance of the busbar voltage attendant upon the action of the devices responsive to current exchanged between the alternators.

2. Means for controlling the amplitude and frequency of oscillations due to hunting ofa system of alternators feeding busbars in parallel, comprising a series trans- I former inserted in the mains of the alternator, a commutator machine connected to the secondary circuit of the series transformer, said commutator machine feeding the field coils of the alternator or alternators and providing a counter-compounding action in such manner that an instantaneous increase of the series watt current exchanged between the alternators causes a diminution of the field current, combined with means for'regulating the transformation ratio of the series transformer, and with an automatic slow-acting field control device for restoring at the busbars the proper regulation of the distribution voltage.

'transforming our i comprising a separate field magnet winding placed on the field magnets of the exciter and means at the generator station for supplying an independent exciting current to such windin 4. Means ir controlling the amplitude of oscillations due to hunting of a system of alternators feeding busbars in parallel, comprising a series transformer inserted in the mains of the alternator, and a commutator machine connected to the secondary circuit of the series transformer, said commutator machine feeding the field coils of the alternator or alternators and providing a counter-compounding action in such manner that an increase of the series current causes a diminution of the field current, combined with an automatic voltage regulator for correcting the mean value of the variations in voltage independently of the periodic variation produced by the said oscillations due to hunting.

5. Means for reducing the amplitude and frequency of the free oscillations of alternators coupled to one another, comprising an exciter for each alternator and means for producing an instantaneous reduction of the electromotive force of said exciter proportionally with the variations of current exchanged between machines and armature counter ampere turns opposed to the field magnets substantially as described.

6. Means for reducing the amplitude and frequency of the free oscillations to which alternators are subjected when coupled or the maximum current which they first deliver when accidentally short-circu'ited, comprising means for transforming current exchanged between the machines and means for utilizing the transformed current to produce an instantaneous reduction in the field excitation of an alternator.

7 Means for reducing the hunting action of alternators coupled in'parallel or the maximum current delivered when short-circuited, comprising means for transforming alternating current exchanged between the alternators and means for utilizing the transformed current to produce a diminution of the exciting current of an alternator.

8. The combination with a system of alternators having fields each excited by a current from a rot y converter, means for ant flowing in series between the alternators and means for utilizing the transformed current to cause diminution of said exciting current in accordance with an increase of said series current thereby controlling the amplitude and frequency of the free oscillations due to hunting action of the system.

9. The combination with an alternator,

of a compound exciter therefor, means for instantaneously producing a diminution of the electromotive force applied at the terminals of the exciting winding and field magnets by the action of the increased current delivered by the alternator and means for producing automatic, relatively slow regulation of the field excitation to maintain the difference of potential constant.

10. The combination with an alternator, of a counter-compounding exciter and a series transformer feeding current to the exciter, said exciter acting on sudden increase of or diminution of series current to cause an instantaneous diminution or increase of the field current in combination with a slowacting controlling device for the field excitation of the alternator producing a slow increase or decrease thereof.

11. The combination with an alternator, of a rotary converter operated by alternating current and supplying exciting current for the alternator field, a transformer in a series connection from saidalternator to the mains, a transformer in parallel or connected across the terminals of the machine and connections between the secondaries of said transformers and the alternating side of the converter to feed said converter with current compounded from said transformers, and an independently acting automatic selfexcitation regulator for the field of said converter acting oppositely to said compound ing device.

12. The combination with an alternator, of a rotary converter supplying exciting current for the field alternator and fed on its alternating current side with current from transformers, series and parallel, an automatic self-excitation regulator for the field of said converter and a continuous supplementary excitation through an independent circuit for stabilizing the exciter.

13. The combination with an alternator, of a rotary converter feeding the field of the alternator, a series transformer inserted in a main of the alternator and feeding alternating current to the alternating side of the rotary converter, said converter supplying diminishing current to the field of the alternator on increase of series current in the transformer and means for partially exciting the field of the rotary converter by variable currents generated in the field magnet circuit of the alternator by oscillations of the alternator or sudden overcharge.

In testimony whereof I have signed this specification.

ANDRE BLONDEL. Witnesses:

Fnnnnaro HARLii, HENRY T. Wmoox.

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