US2789253A - Protection of circuit breakers and metallic switches for carrying large currents - Google Patents

Description

April 16, 1957 A. VANG 2,789,253 PROTECTION OF CIRCUIT BREAKERS AND METALLIC SWITCHES FOR CARRYING LARGE CURRENTS Filed Dec. 28, 1951 150 INVENTOR.

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A TTORNEK United States Patent PROTECTION OF CIRCUIT BREAKERS AND METALLIC SWITCHES FOR CARRYING LARGE CURRENTS Alfred Vang, Carmel, Calif. Application December 28, 1951, Serial No. 263,932

3 Claims. (Cl. 317-11 This invention relates to the protection of circuit breakers and metallic switches for carrying large currents.

As heretofore produced, circuit breakers have been constructed from massive conductors consisting of expensive and scarce metal, such as silver or copper, not only to assure a conductor of sufficient size to carry the anticipated currents, but also to allow for inevitable deterioration at contact zones. This deterioration occurs in the form of vaporization of the costly metal, simple melting and subsequent solidification in molecules, as well as oxidation.

Not only is there a loss of expensive metal in the zones of actual contact but a Waste of metal in the conductors as a whole, since heavier construction of the conductors is necessary to mechanically carry the contact, portions which must be over-size, when first installed, to allow for the mentioned loss. In automatic breakers the heavier construction necessitates larger magnets or solenoids, requiring still more copper for their windings.

Many attempts have been made to prevent the burning of breaker points, such as the provision of tripping devices, magnetic blow out devices, are chutes, and horn vapors, the most eflicient manner for controlling arcing is to prevent any vaporization at all of the contact metal. This may not always be attainable, but the sooner the gap potential is reduced the more easily any arcing is extinguished because the temperature of the metal is kept lower. Consequently an opposing voltage, and an ever increasing air gap, can more effectively control an arc than either alone, and the sooner the opposing voltage is brought into play the better because of the lower temperature and decreased tendency to vaporize the metal.

In the drawing:

Figure 1 shows a breaker system for direct current, and

Figure 2 shows a system for alternating current similar to the system of Figure 1.

The invention as shown in Figure 1 comprises a source of direct current a at S182 connected to a load L by means of conductors such as wires 10 and 11. A circuit breaker having a movable member such as a knife switch 12 having a blade 13 is interposed between the source and load.

Connected to bridge the switch 12 is a charged capacitor or condenser 14 of opposite polarity to that assumed by the terminals of the switch, when the latter is opened, the connection being through ordinary conductors 15 and 16 but with a non-linear conductor or any kind of transductor, for example a triode 18 interposed in one of the conductors 15 or 16. The triode is preferably of the mercury pool type such as shown in my Patent No. 2,287,541, or a thyratron.

The triode is triggered by a momentary passage of current originating with a change of resistance at the circuit breaker, as the blade 13 leaves the breaker contact 19.

gaps, to mention only a few. The great variety of devices in use generally, merely points out the fact that none has heretofore been found generally satisfactory for operations in the free air.

When combustible material is present in the surrounding atmosphere, a condition existing in coal mines, flour mills, oil well locations and even in ordinary use of electric locomotives and cars, the circuit breakers must be enclosed to prevent explosion or fire.

Immersing the breaker in oil has been to advantage in the mere interruption of current, but the use of oil introduces difliculties of a new sort, especially fire hazards and the careful attention to the oil to reduce oxidation and deterioration. Even so decomposition occurs, with the formation of conducive carbon, and filters and circulation pumps are required to maintain the oil in proper condition.

One object of this invention is, therefore, to provide a simple means for preventing or minimizing arcing in arr as the breaker is opened.

Another object is to provide means for neutralizing the potential difference across the gap as the breaker is opened.

Still another object is to provide means, whereby a condenser may be employed to furnish a neutralizing potential difference.

A further object is to provide a system which, with slight modification, may be applicable to A. C. as well as D. C. breakers.

The attainment of these objects is accomplished by electronically connecting a previously charged condenser across the breaker gap at the instant the arc begins to form. The polarity of the charged condenser is opposite to that of the incipient arc gap so as to neutralize the potential difference across it. Since arc formation is largely a result of the formation of highly heated metal The blade 13 is provided with an extension 20 which is in contact with a minor contact member 21 and remains in contact therewith until the breaker is well open relative to contact 19 after which the extension is clear of the member 21.

The incipient opening of the main switch thus causes a potential difference pulse to be impressed between the points 19 and 20 which pulse is applied to the primary 22 of a transformer 23 through conductors 24 and 25.

A condenser 26 interposed in one of the conductors 24 and 25 prevents a continued flow of current through the p y The primary pulse develops a corresponding pulse in the secondary 27 of the transformer 23 which imparts a potential difference between the control element or grid 28 and the cathode 29 of the triode to render same conductive.

A source of current generally designed as 30 is provided for grid bias. V

The bias on grid 28 is normally sufficiently negative to render the triode non-conductive. The pulse of the secondary 27 imparts a sufliciently positive charge to the grid, as shown, to render the triode conductive.

In operation, incipient opening of the breaker causes a potential difference thereacross to produce a voltage pulse to trigger the triode, throwing opposite potentials of the capacitor 14 across the gap so as to minimize or prevent arcing thereat.

The switch or breaker 12 is diagrammatically shown and conventional brush-type breakers, for example, can be modified by those skilled in the art to eflfect the same action.

While the above system is satisfactory for D. C. breakers it is not asapplicable to A. C. work, for while the polarity of the capacitor might happen to be correct when A. C. is interrupted, there is equal probability that the capacitor will augment rather than diminish the arc.

. 3 To overcome this objection I employ two capacitors one to oppose one half cycle of the gaps potential difference and the other capacitor to oppose the other half cycle. In Figure .2, a source of A. C., 8.284, is connected. to a load L by means of'conductors. 110 and 111 through the switch 12. Condensers 114 and 114:: of opposite charge are both bridged across the switch 12 by conductors 115, 116 and 115a, 116a with triodes, suchas thyratrons 113 and 118a, being interposed between the respective condensers and the switch gap so that the potential of one or the other of the condensers may be selectively'applied across the switch gap to oppose arcing when the switch is' opened under. load.

Thus far it may be said that the A. C. suppression system is identical with that described .of the D. C. systern withthe exception that two insteadcf. one capacitor may be thrown across the gap one being of one polarity and the other of the opposite.

Likewise as inFigure 1, upon opening of the. breaker, a pulse is applied to the primary 122 of a transformer 123. The transformer. 123, however has two secondaries 127 and 127a, the former being connected to grid 128 and cathode 129 of triode 11% and the latter to the corresponding elements 128a and 1290 of triode 118a. The terminals .of the two secondaries are so connected to the two triodes that for the same pulse in the primary a negative increment of electricity is applied to the grid of one triode and a positive increment applied to the grid of the other.

The transformer 123 is a segrcgator for translating the pulse current into two separate control currents. Grid bias potentials are provided for by means 13.0 and 13% similar to that employed in Figure l at 30.

The operation of the system of Figure 2 is similar to that of Figure 1. g

A condenser 126 may be interposed in the primary circuit of the transformer 122 to protect same as a resistor and so that the combination shown in Figure 2 will be suitable for use on D. C. as well.

However, only one of the condensers 114 or 114a is discharged at a time since the two control grids are always oppositely charged relative to their associated cathodes.

This condition also prevents the two condensers from being effectively connected to each other, it being noted that the plates 131 and 131a of each tr-iodeare connected respectively to the positive side of associated condensers.

This is also true of plate 31.

The grid bias is preferably variable and may be chosen to suitoperating conditions most prevalent in the load circuit.

The capacitors 14, 114 and 114a are chosen to be sufficient to extinguish or prevent an arc, depending on the load.

They may be charged by various means as will be apparent to those skilled in the art, and their voltage may be varied considerably depending on the nature of the load circuit. 7 V

I claim as my invention:

1. A sub-combination for preventing arcs when a load circuit is opened comprising switch means having a movable arm and main and auxiliary contact members for engagement therewith, themovement of the arm being so constrained that thelatter in afirst position engages both members and in a second position engages only the auxiliary member, said arm being permanently and directly connected to a conductor in the load circuit; a condenser and meansfor charging same, and means for discharging the-condenseracross the-arm and main member in opposition to load current tending to are across the switch means as the arm is movedfrom the first to second position.

2. In combination, a source of alternating current, a circuit breaker, and. load all in series; twopolarized condensers and means .for charging same; the circuit breaker having blade and contact members; the two condensers tending toimpart a potential difference across the members in one directionand the other in the oppositedirection; two triode valves, each valve'interposed in respective conductors connecting the condensers to the members and-having a control element for rendering the valve conductive; a transformer; a control circuit including the primary .of the transformer; means for diverting a portion of said current through the control circuit as the circuit breaker opens; said transformer having secondary turns for delivering output to control the conductance ,of the valves; said turns being connectedto the respective control elements and cathodes so that the output .tends to render one valve conductive and the other non-conductive, the conductance and non-conductance of the valves depending on the polarity of the turns connected to the respective control elements and cathodes.

3. In combination as in claim next above, said means including an extension on said blade member and an auxiliary contact therefor.

References Cited in the file of this patent UNITED STATES PATENTS 1,406,234 Slepian Feb. 14, 1922 1,421,170 Chubb June 27, 1922 1,681,196 Rudenberg et al Aug. 21, 1928 1,792,340 Wellman Feb. 10, 1931 2,043,822 Young June 9, 1936 2,094,361 Lee Sept. 28, 1937 2,196,820 Verse Apr. 9, 1940 2,292,174 Suits Aug. 4, 1942 2,537,383 Van Dorsten Jan. 9, 1951 2,610,231 Wettstcin Sept. 9, 1952 2,665,396 Weinfurt Jan. 5, 1954 FOREIGN PATENTS 894,223 France Dec. 18, 1944

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