US2327578A - Parallel operation of regulator interrupters - Google Patents

Description

Aug. 24, 1943. H. J. BROWN 2,327,578 PARALLEL OPERATION OF REGULATOR INTERRUPTER Original 3119a Jan. 31,1942

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Patented Aug. 24, 1943 PARALLEL OPERATION OF REGULATOR m'rERRurrERs Harold J. Brown, Indianapolis, Ind.

Original application January 31, 1942, Serial No. 429,075. Divided and this application January 23, 1943, Serial No. 473,304

6 Claims. (01. 1171-229) My invention relates in general to circuit interrupting systems and more particularly to a circuit interrupting system in a generator field regulating circuit having a circuit interrupting device therefor with at least two parallel sets of interrupting mean substantially simultaneously operated for jointly supplying a current through a plurality of parallel interrupting paths to the electrical system.

This application is a division of my pending application Serial Number 429,075, filed January. 31, 1942, for Parallel operation of interrupting means.

In the design of an interrupting devicefor a load circuit, substantially no difficulty is encountered in building an interrupting device that is immune to mechanical wear on the contact points. The impacts on closing and the wear due when the contact engagement is made, as the condensers necessary to operate the equipment are then charged or discharged. One of the more noticeable efiects is material transfer from one contact to the other, another is pitting and erosion, and in severe cases, there is arcing which is very destructive.

to rubbing can be so reduced that the device will operate indefinitely, if at the same time, the stressed parts are properly strain-relieved and operated well below their indurance limit. With such an interrupting device, the problem is primarily one of reducing the eifects of the electrical current and voltages on the contacts so that any required performance may be achieved. Experience shows that in an interrupting device where the make-and-break operating cycles run into the billions, the life and performance is strictly determined by the ability of the contact points to withstand the pitting and erosion of the electrical current flowing at the instant of the make-and-break. Notwithstanding the fact that the most resistant materialsavailable to the engineering art are used, the interrupting device in many applications fails to meet the standards of reliability and life which are normally re- .quired. Interrupting devices with several sets of contact points in parallel have also been used in an effort to increase the life thereof, but here, too, the life and reliability of the contacts do not come up to expectations. The principal reason for the lack of satisfactory results liesin the character of the contacting materials when interrupting the current. Generally speaking, the current in a contact "necks down to an extremely high current density prior to separation, even though large shunting capacities and other ourrent-diverting impedances be used. For reasonable values of current relative to the material used, the contact is subject to melting andvaporization at the final tip, and if two or more contacts are in parallel, the final single trailing contact is subject to the attack of this high current density. Similar destructive effects take place Contact point disintegration due to electrical current falls in two categories; namely, the disintegration resulting from making the contact and the disintegration resulting from breaking the contact. the proper handling of the circuit constants but it is unfortunately true that changes in the circuit which improve the performance at the break may harm the performance at the make, and vice versa. Therefore, the design of. a good and efficient interrupting circuit which will give long life and reliability against breakdowns presents a difficult problem to solve and a satisfactory circuit cannot be prescribed on the basis of a superficial examination. Furthermore, the absence of sparking is'no criterion of a satisfactory circuit, as it is often true that the performance of mildly sparking contacts will be superior to dark ones. A further characteristic of contact points is that various thresholds of the current flowing through one interrupting means from diverting into another, as one interrupting means is interrupted prior to another.

Another object of my invention is to forcibly prevent the current flowing in two or more interrupting contact 'from-re-establishing itself in a single final trailing contact tip during the short interval of time involved between the successive Openings of the parallel contacts and to insure that the burden of interrupting the circuit is divided between the pair of parallel contacts. Another object of my invention is the provision, in a circuit interrupter having a plurality of parallel interrupting paths, of preventing the current which is, interrupted in an interrupted path incident to slight variations in the interruption of the plurality of interrupting paths from suddenly ire-establishing itself in a yet uninterrupted path durlng the short interval of Both may be partially controlled by,

time involved between the successive interruptions or the parallel paths.

Another object of my invention is to keep the flow or the interrupting current in the interrupting contacts less than that certain threshold value below which material transfer and erosion of the contacts do not occur at all or in small amounts. I

In a set of parallel contacts, the current will divide between the contacts according to Ohms law. Since the contact resistance is small compared to the rest of the load circuit, which is ordinarily the case, the opening of one of two parallel-contacts will not efiect the total current flow, and the total current will then flow through the remaining closed trailing contact. The time required for this diversion will be very small, perhaps less than seconds, as indicated by the residual inductance and resistance of the closed loops through the two parallel contacts; In any practical interrupter, the differences in opening time may be a thousand times this value so the problem may be stated as one of increasing the diversion time perhaps a thousand or more times its ordinary value.

Therefore, another object of my invention is to provide ior increasing the diversion time perhaps a thousand or more times its ordinary value. Another object of my invention is the provision of the employment of a balancing inductance in combination with a current-diverting impedance to forcibly prevent the current flowing-in two or more interrupting contacts from re-establishof a T-connected inductance which does not increase the impedance to the flow of the load current'butwhich developed an inductive impedance to the flow of the current in the parallel sets of contacts to oppose the sudden re-establishment of the current-of an interrupted parallel contact path during the short interval involved between the successive openings of the parallel set of contacts in the yet uninterrupted parallel paths, thereby preventing the damaging oi the contacts.

Another object of my invention is the provision in a circuit interrupting device of reducing the electrical damage to the contacts during both the make and break cycles thereof.

Other objects and a fuller understanding of my invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing; in which:

The figure is a diagrammatic illustration of a generator field circuit embodying the features of myinvention.

With-reference to the figure of the drawing, I show the employment of my current-interrupting system in a generator field regulating circuit, which comprises, a generator 32 having a field winding 33, a balancing inductance 34, an electro-magnet 31, and a governing relay M. "The current through the field winding 33 is governed the electro-magnet 37 through a mechanical motion transmitting arrangement illustrated by the dash and dot lines 38. The electro-magnet 31 comprises two windingsin which one of the coils is energized by current from'the generator which flows through conductors 42 and 43 and in which the other coil therein is energized by current which flows through conductors M and 43. The current which flows through the coil connected to the conductorsM and 43is governed by the governing relay M which is in turn by the interrupting set of parallel contacts 35 and36 having respectively in parallel therewith the resistors wand 39 which act as current-diverting impedances. As illustrated diagrammatically, the contacts 3;; and 36 are actuated by connected across the generator terminals. Therefore, when the relay M closes its contact the electro-magnet 3! operates instantaneously to actuate the contacts 35 and 36.

The balancing inductance 34 operates to prevent the establishment of the current from an interrupted contact from suddenly re-establishing itself into the other contact during the interval between the successive openings of the contacts to insure a proper division of the current between the parallel contacts. The balancing inductance 33 has a center-tap dividing the inductanceinto two halves with a half thereof included in each of the two parallel interrupting paths. The center tap of the inductance is connected to the upper end of the field winding 33, and in operation the field load current divides substantially equally between the two sets of parallel contacts 35 and 36 when the contacts are closed. The flowing of the field current through the two halves of the balancing inductance balances out the inductance impedance in the windings with respect to the field load circuit. Con

sequently, I am able to achieve parallel operation without liability of inductance in the load field circuit. The only efiectupon the load field circuit will be that of IR drop which may exist.

During the interruption of the parallel interrupting means should the contacts 35, for example, open lightly prior to the-opening of the contacts 36, then the combination of the balancing inductance and the current diverting impedance operates to oppose the sudden re-establishment of the current flowing through the interrupted contacts 35 in the yet uninterrupted contacts 36 during the short interval involved between the successive opening of the two sets of contacts, thereby preventing the damaging of the contacts. The reverse situation would occur should the con-: tacts 35 open slightly prior to the opening of the contacts 35. The resistors 39 and 63 are each substantially one-half of the capacity of what a single resistor would be ifit were connected across a single set of contacts. Summarizing, my

invention includes the arrangement for preventing the current which is interrupted in an interrupted parallel contact path incident to slight variations in the breaking of the plurality of sets of contact means from suddenly re-establishing itself in a yet uninterrupted parallel contact path during the short interval of time involved between the successive openings of the contact means'to prevent the damaging of the contacts.

While I have illustrated and described my-invention as having particular utility in connection with interrupting parallel contacts, it is to. be understood that my invention is not limited thereto and,- therefore, includes any interrupt-' ing system comprising interrupting mean having a plurality of parallel interrupting paths which are substantially simultaneously interrupted for jointly interrupting the current in the electrical system.

Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim as my invention:

1. In a generator field circuit having a regu-- lating device therefor with at least two parallel sets of interrupting contacts substantially simultaneously operated for jointly supplying a cur-- rent through a plurality of parallel contact paths to the field circuit; the arrangement for preventing the current which is interrupted in an interrupted parallel contact path incident to slight variations in the breaking of the plurality of sets of contacts from suddenly re-establishin itself in a yet uninterrupted parallel contact path and increasing the burden on he set of contacts therein during the short interval involved between the successive openings of the parallel sets of contacts, said arrangement comprising the combination of resistance means connected across the contacts of each set of contacts, and a balancing inductance having a winding with two ends and a center-tap dividing the said winding into two halves with a half thereof included in each of the two parallel contact path for developing, in series with each of the parallel sets of contacts, an inductive impedance to the flow of current therein, the inductive impedance in the yet uninterrupted parallel contact'path opposing the'sudden-re-establishment of the current of the interrupted parallel contact path during the short interval involved between the successive openings of the parallel sets of contacts in the yet uninterrupted parallel path, thereby preventing the damaging oi th contacts, the said center-tap being connected to the field circuit and the said ends of the balancing winding being connected respectively to the two parallel contact paths, thus forming a T-connection to balance out the inductive impedance of the said winding with respect to the field circuit.

2. In a generator field circuit having a, regulating device therefor with at least two parallel sets of interrupting contacts substantially simultaneously operated for jointly supplying a current through a pluralityof parallel contact paths to the field circuit; the arrangement for preventing the current which is interrupted in an interrupted parallel contact path incident to slight variations in the breaking of the plurality of'sets of contacts from suddenly re-establishing itself in a yet uninterrupted parallel contact path and increasing the burden on the set of contacts therein during the short interval involved between the successive openings of the parallel sets of contacts, said arrangement comprising the combination of impedance means connected across the contacts of each set-of contacts, and a balancing inductance having a winding with two ends and a center-tap dividing the said winding into two halves with a half thereof included in each of the two parallel contact'paths for developing, in series with each of the parallel sets of contacts, an inductive impedance to the flow of current therein, the inductive impedanc in the yet uninterrupted parallel contact path opposing the sudden re-establishment of the current of the interrupted parallel contact path during the short interval involved between the successive openings of the parallel sets of contacts in the yet uninterrupted parallel path, thereby preventing the damaging of the contacts, the said center-tap. being connected to the field circuit and the said ends of the balancing windin being connected respectively to the two parallel contact paths, thus forming a T-connection t balance out the inductive impedance of the said winding with respect to the field circuit.

3. In a generator-field circuit having interrupting means therefor, said interrupting means having a plurality of parallel interrupting paths, said parallel paths being substantially simultaneously interrupted by the interrupting means for jointly interrupting the current in the generator field circuit, current-diverting means connected in effective current-diverting relation with the parallel paths, and balancing inductance means having a plurality of inductance windings, each inductance winding being respectively con nected in series with the interrupting parallel paths for developing, in series with each of the interrupting parallel paths, an inductive impedance to the flow of the current therein, said plurality of inductance windings having tap connection means to establish opposing fluxes therein to minimize the inductive impedance to the flow of the current in the system.

4. In a generator field circuit having interrupting means therefor, said interrupting means having two parallel interrupting paths, said parallel paths being substantially simultaneously interrupted by the interrupting means for jointly interrupting the current in the generator field circuit, current-diverting means connected in effective current-diverting relation with the parallel paths, and balancing inductance means having a balancing winding with a center-tap connection dividing the said balancing winding into two halves with a half thereof connected in series with each of the interrupting parallel paths for developing, in series with each of the said interrupting parallel paths an inductive impedance to the flow of the current therein.

5. In a generator field circuit having interrupting means therefor, said interrupting means having a plurality of parallel interrupting paths, said parallel paths being substantially simultaneously interrupted by the interrupting means for jointly interrupting the current in the generator field circuit, current-diverting means connected in effective current-diverting relation with the parallel paths, and balancing inductance means having a plurality of inductance windings, each inductance winding being respectively connected P in series with the interrupting parallel paths, an

inductive impedance to the flow of the current therein, said plurality of inductance windings having tap connection means to establish opposing fluxes therein to minimize the inductive impedanceto the flow of the current in the system, said current-diverting means comprising resistance means having a plurality of parts, with a part connected in shunt with the interrupting means of each parallel path, said parts operating to limit the field current when said parallel Paths are interrupted.

6. In a generator field circuit having interrupting means therefor, said interrupting means having a plurality of parallel interrupting paths, said parallel paths being substantially'simultaneously interrupted by the interrupting means forjointly interrupting the current in the gening respectively connected in series with the'interrupting parallel paths for developing in series with each of the interrupting parallel paths, an

inductive impedance to the ilow of the current therein, the inductive impedance in th et uninterrupted parallel path in combination with the current-diverting means opposing the sudden reestablishment of the current of an interrupted parallel path during the short interval involved between the successive interruptions of the parallel paths in the yet uninterrupted path, thereby,

preventing the damaging of the interrupting means, said inductance windings ofthe inductance means having tap connection means to establish opposing fluxes in the windings to min- .i nize the inductive impedance to the flow of the current in the system.

HAROLD J. BROWN.

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