US1882162A - Device for connecting and switching the windings of dynamos - Google Patents

Description

E. ROSENBERG Oct. 11,1932.

DEVICE FOR CONNECTING AND SWITCHING THE WINDINGS OF DYNAMOS Filed May 17, 1929 2 Sheets-Sheet l r g en 's I JNveM Ta o1. 11,1932. ERQSE ERG 1 1,882,162

DEVICE FOR CONNECTING AND SWITCHING THE WINDINGS OF DYNAMOS Filed May 17,- 1929 Sheets-Sheet 2 I MM a. 11, 10.32

EMANUEL BOsENIBERG, 0F 'WEIZ, AUSTRIA DEVICE FOR CONNECTING AN D SWITCHING TEE WINDINGSOF DYNAMICS Application med May 17, 1929, Serial No. 384,009, and in Austria May 25, 1928.

In circuits subject to varying electro-motive force a certain amount of resistance is advanta eous or even necessary for the purpose of amping oscillations. A case of such necessity is the feeding of an electric-arc by means of a dynamo possessing a voltage characteristic suitable to this particular purpose, i. e. diminishing of voltage with the increase of amperage. Changes in the counter 1 electro-motive force set up'by the arc bring about corresponding changes in the current and thereby in the'voltage of the dynamo, not simultaneously but with a certain retardation caused by self-induction and residual magnetism. During this retardation waves of current arise which are only damped by v the resistance of the circuit. "Insufficient resistance gives rise in certain cases to disadvantageous efiects, especially wherethin metal electrodes are concerned, in which case too much current can cause momentary overheating of the tip of the electrode and consequent spraying of the molten electrode metal, while too little current causes too great a coolingofi of the electrode and under unfavourable circumstances the extinction of the arc.

7 Experience has shown that a dynamo which works satisfactorily from normal down to half normal amperage gives rise to difiiculties when thin electrodes are used requiring considerably less current, and that these difliculties can be overcome by inserting in the welding-circuit a resistance which, together with the internal resistance of the dynamo and the remaining resistance of the welding-circuit, produces a voltage-drop of several volts, for instance in the case of a certain electrode 3-4 volts.

The addition of an external resistance is a 40 clumsy expedient and does not insure its use by the welder solely when low amperage is required. An automatic switch 'can of course be provided to'short-circuit the additional resistance when a certain amperage-limit is reached, but such devices can fail to operate and in any case mean additional costs for purchase and upkeep.

According to the present invention the peculiar internal connection of the dynamo itself alters the internal resistance in the sense and to the extent which has proved requisite for the current at any one time being used. T he adaptation concerned can be employed for dynamos in which the field is produced by means of series-winding, as well as forts such in which a series-winding'is employed to weaken the field A cross-field dynamo can serve as the first explanatory example. Generators of this type are suitable for the feeding of an arc, 59

whether provided, with regulating poles or not. The primary field is excited by a winding connected in series with the main brushes Q of the armature and the external circuit, the

main brushes having contactwith commu- 5' tater-segments belonging to armature-com doctors in the middle of the pole shoes, while auxiliary brushes (situated in the normal neutral zone) are connected together and cause, for instance in a two-pole armature, to current to be conducted firom one armature quarter into the diametrically opposite one, so that the armature-reaction gives one component at right angles to the primar field and another in straight opposition to the prif5 mary field. A part of the field possesses slight core cross-section, so that a high degree of magnetic saturation occurs here. In the case of a generator without regulating poles a re achieved within certain limits by means of a resistance in parallel to the series-winding; In the case of a generator with regulating poles the highly saturated cross-section can be altered at will by'adjustment of an iron 5 body within the magnetic circuit, so that the generator'can be set to various short-circuit currents without alteration in the windings. Let it be supposed that a dynamo built for 400 amp. maximum current possesses just 99 lation of the current can he mutator the alteration of the resistance is' effected in the field-coils alone. The seriescoil possesses normally far less resistance than the armature. In order therefore to double the internal resistance of the generator without altering the armature-resistance, it may be necessar to increase the resistance of the field-coils ourfold or even more. .This can be achieved in various ways. Fig. 1 shows diagrammatically one arrangement of field coils in a dynamo constructed in accordance with my invention and also the manner in which the dynamo may be connected to the work circuit.

Fig. 2 is a perspective view partly in section of a field coil showing one manner of arranging the high and low resistance windm ig. 3 is a view similar to Fig. 2 showing a field coil of modified constructwn.

Figs. 4, 5 and 6 are diagrammatic views of modified forms ofdynamos forming the subject matter of the present invention and disclosing various arrangements of the field coils and the manner of connecting the dynamos to working circuits.

Referring more particularly to the accompanyin drawings, I have shown in Fig. 2 one type of constructlon of the field-coils. As here shown the coils are wound with two con ductors, of which the one indicated at 11 has a far smaller cross-section than the other indicated at 12 and is intended for the lesser current. For the lesser current the thinner conductor 11 alone can be used, for the full current either the thicker conductor 12 alone or connected in parallel with the thinner conductor 11,.

It is advantageous to carry out the wind-' ing in such a manner that the thin conductors are surrounded by the thick, so that the heat generated in the thin conductors can be transferred to the thicker, when the latter are free' of current. This is most easlly achieved in the case of strip-conductors by winding simultaneously the thlck and thin copper strips, which are insulated from each other. This arrangement is clearly shown in Fig. 2. If the thin conductor is to carry possible even to better the load-limit of the generator. In Fig. 3 I have shown a coil of this type wherein the thick conductor is wound on the inside and the thin on the outside of the coil; the mean winding-length of the thin conductor is therefore greater than that of the thick, and in this way also an increase of resistance is attained.

However, the disposition hitherto described provides no security against the mistaken use by the welder, when working with heavy wires, of the Winding which is dimensioned for li ht wires only, or against the overheating 0 the coil which would follow from this practice. In order to combat this danger the thin-wire coil can be provided with a smaller number of effective turns than the thick-wire coil. To take a definite case, a reduction to 60% in the number of field-coil turns for instance reduces the highest attainable armature-current by half. An overloading can therefore be checked by providing the thinwire winding with fewer effective turns. This can be effected either by giving the thin-wirewinding actually fewer turns as shown in Fig. 4 wherein the thick wire winding is indicated at 22 and the thin wire winding as at- 21, or by giving it the same number of turns as the thick-wire winding but connecting a part a of them in the opposite direction to the rest as shown in Fig. 5. Inthis arrangement substantially 80% of the winding 32 is in the same direction as the thick-wire winding 22 and substantially 20% comprised in coil 31 in the opposite direction, so that only 80%20%=60% of the turns of the thinwire winding, are magnetically effective, as against of the thick-wire winding.

In another t pe of construction embodying the present lnvention a thin-wire counterwinding is employed as shown in Fig. 1. The thick-wire winding 22 remains permanently connected, and, for the attainment of increased resistance and diminished current intensity, is connected in series with the thinwire winding 36 the smaller part of which is wound in the same direction while the greater part is wound in the opposite direction to the winding 22 and possesses say an excess of 40% opposing turns, so that the number of effective turns is 100%40%= 60%, while the ohmic resistances of both the thickand thin-wire windings are connecte T in series. For the purpose of attaining full current and slight internal resistance the thin-wire winding can be short-circuited or the external circuit connected to a terminal situated between the thick and thin windings.

A further practical realization of this invention is shown in Fig. 6 and consists in having two winding-halves with unequal numbers of turns, and connecting them in parallel for working at full current, and opposed for working at diminished current. There could be for instance one winding 41 of and another winding 42 of 10 tiirn's. Should they chance to possess equal resistance on account of the difference in mean length of turn between them, then, in the case of parallel connection each would carry one half of the current and they would behave like a coil of 15 turns carrying the full current. If they are counter-connected they behave like a coil of 20-10=10 turns. The resistance in the latter case is four times as great as in the case of parallel connection.

A generator in which the primary field (in whichever manner excited) is weakened by a counteracting series-winding as the current increases (compound-wound generator) can also be used for arc-welding. In this case again a thin-wire difierential compound- I winding can be used possessing several times the resistance of the thick-wire winding. The thin winding, to prevent overloading,

can be given more turns than the thick. It.

for instance the primary field, with constant separate excitation, possesses 5000 ampereturns and if the thick-wire differential com pound winding possesses 10 turns, and the external circuit be short-circuited, the current can rise to 500 amp. before the primary field is cancelled. If the thin-wire winding is carried out with 20 turns and alone connected to the current circuit the primary field is cancelled at 250 amp. 1

Instead of the thin-wire Winding of 20 turns two similar windings of 10 turns each can be provided, each calculated for half the current. They are connected in parallel for full current, and in series and in the same sense for half current.

It is of course also permissible to connect two windings, unequal'in number of turns, in series and in the same sensefor instance a thick-wire winding of 10 and a thin-wire winding of 20 turns, in which case the primary field is cancelled at 167 amp.

In the several modifications above referred to conventional switching means may be employed to connect the thick and thin field coils in any desired relation with the rotor windin For instance, in Fig. 1 the switch blade 3 when in full line position connects the thick winding 22 and short circuits the thin winding 36 whereas when the switch is in the dotted line position the two windings are in series.

Likewise in Fig. 4 when'the switch blade is in full line positions and in contact with the terminal 28 only, the thick wire winding '22 is connected in series with the armature but when .the switch is in connection with terminal 29 only the thin wire winding 21 is in circuit. a

In Fig. 5 the switch as shown in full line positions connects only the thin wire windmg while when in the dotted line pos1t1on connects only the thick wire winding.

In Fig. 6 two switch blades 43 are shown which, when in the full line positions connect the windings 4:1 and 42 in parallel whereas when the switch blades 43 are moved to the dotted line positions the coils 41 and 42 are connected in series. v

. In Figs. 1, 4c and 6 the main or working leads from the dynamo are indicated by numerals 23 and 24: whereas the electrodes are indicated as 25 and 26.

Throughout the foregoing the expressions thin-. and thick-wire windings have been used under the assumption that each winding consists of the same material, and that increaseof resistance is brought about by decrease of the conductor cross-section. There remains however the further alternative of using material of high specific resistance and larger cross-section.

1. In a series wound dynamo, a field structure including plural field windings, an armature provided with a commutator and two sets of brushes, one set of brushes short circuiting the armature on a line displaced 90 electric degrees from the line of field magnetization and the second set of brushes displaced. 90 electric degrees from the first set and connected to an external circuit, and means for selectively connecting one of the brushes of the second set to one of the field and having at least some of its turns wound in opposition to those of another field winding, an armature provided with a commutator and two sets of brushes, one set of brushes short circuiting the armature on a line displaced electric degrees from the line of field magnetization, a second set of brushes displaced 90 electric degrees from the first set and connected to an external circuit, and means for selectively connecting one of the brushes of the second set to said field windin'gs to produce simultaneously a relatively high internal resistance for the dynamo and a relatively weak efi'ective field flux.

3. A dynamo for feeding an electric arcwelding circuit, comprising an armature provided with a commutator and two sets of brushes displaced 90 electric degrees to each other, one set of brushes short circuiting the are main field winding so as to reduce substantially the effective number of turns of the field winding when connected with the second set of brushes, and means for connecting the second set of brushes with said high resistance field winding.

4. In a series wound dynamo including a field structure, a series field winding, an armature provided with a commutator and two sets of brushes, one set of said brushes being short.circuited on itself and the other being connected to an external circuit, and means for changing the internal resistance of the dynamoin inverse relation to the number of effective magnetizing turns of the field winding.

5. A dynamo for feeding an electric arc welding-circuit, comprising an armature provided with a commutator and two sets of brushes displaced electric degrees to each other, one set of brushes short circuiting the armature and the second set of brushes connected to the arc welding circuit, a field structure containing a main series winding and an auxiliary winding and disposed with reference to the main field Winding so as to reduce substantially the effective number of turnsof the field winding when connected with the second set of brushes, and means for "changing the internal resistance of the dynanio in inverse relation to the number of effective magnetizing turns of the field winding.

6. A dynamo for feeding electrodes in an electric arc welding circuit comprising an armature provided with a commutator and two sets of brushes, one set of brushes short circuiting the armature on a line displaced 90 electric degrees from the line of field mag netization and the second set of brushes displaced 90 electric degrees from the first set and connected to the arc-welding circuit, a field structure containing a main series winding and an auxiliary winding disposed with reference to the main field winding.so as to reduce its magnetizing effect when connected with the arc-welding circuit, and means for changing the magnetizing effect of the field winding in direct relation and simultaneous ly the internal resistance of the dynamo in inverse relation to the thickness of the electrodes.

In testimony whereof I-have aifixed my signature.

EMANUEL ROSENBERG.

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