US2586290A - Circuit interrupter - Google Patents

Description

CIRCUIT INTERRUPTER .Filed Nov. l, 1947 2 SHEETS-SHEET l Thoma-Er'ownej fr'.

Feb. 19, 1952 B. P. BAKER ET AL CIRCUIT INTERRUPTER 2 SHEETS- SHEET 2 Filed Nov. l, 1947 III.

generally of the form shown in Fig. 4.

Patented Feb. 19, 1952 CIRCUIT INTERRUPTER Benjamin P. Baker, Turtle Creek, and Thomas E. Browne, Jr., Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 1, 1947, Serial No. 783,602

3 Claims.

This invention relates to circuit interrupters in general, and more particularly to arc-extinguishing structures therefor.

A general object of our invention is to provide an improved circuit interrupter, particularly of the gas-blast type, in which arc extinction is more readily elfected than heretofore and in which trouble due to high surge voltages is avoided during opening of the connected circuit.

A more specific object is to provide an improved circuit interrupter of the gas-blast type in which a shunt including a current limiting valve device of the voltage or frequency sensitive type is employed. Preferably, an auxiliary electrode disposed adjacent to the path of movement of the movable contact is utilized so that the current limiting valve device may be inserted into series circuit during the opening operation.

Still a further object is to provide an improved gas-blast circuit interrupter of the splitter crossblast type in which a probe is utilized in the extinguishing structure, adjacent to which the movable contact moves during the opening operation. Preferably, a current limiting valve device is connected between the probe and the stationary contact to limit voltage surges during the opening operation.

Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings, in which:

Figure 1 is a side elevational view, partially in section, of an improved gas-blast type of circuit interrupter embodying our invention and shown in the closed circuit position;

Fig. 2 is a vertical sectional view through the aro-extinguishing structure of the interrupter shown in Fig. 1, the contacts being shown in the closed circuit position;

Fig. 3 is a vertical sectional View taken along the line III--III of Fig. 2;

Fig. 4 is a graph indicating the circuit voltage, arc voltage and arc current in a circuit of the type to be interrupted; and

Fig. 5 illustrates diagrammatically an arrangement similar to that of Fig. 2, except that a different current limiting valve shunt is employed.

Trouble is sometimes experienced with circuit breakers when opening low or moderate currents in highly inductive circuits due to abnormally high voltage surges which sometimes occur. These abnormal transient over-voltages are caused by too early extinction of the arc formed between the breaker contacts on opening and are Fluid blast breakers in which the blast is independent of the interrupted current magnitude are particularly prone to cause such over-voltages, which may cause failure of the breaker to interrupt the circuit or failure of the insulation of connected apparatus.

Referring to Fig. 4, the reference numeral l indicates the circuit voltage which alternates in sinusoidal fashion, 2 designates the arc current which passes to zero at the point 3, and 4 indicates the magnitude of the arc voltage, the latter being initially 10W before the arc is interrupted and upon interruption of the arc oscillating about the circuit voltage in a manner designated by the reference numeral 5. The oscillating voltage transient 5 nally settles down to the circuit voltage at 6, whereafter the voltage across the open contacts is merely the normal open circuit voltage.

We have found that abnormally high voltage surges indicated by the reference numeral 5 in Fig. 4 not only tend to break down the arc gap to cause reignition of the extinguished arc but also subject the connected apparatus to severe electrical strain.

We have discovered that the use of a voltage limiting device including a plurality of non-linear resistance blocks such as are used in lightning arresters, may be successfully employed in reducing such over-voltages. These valve blocks may, for example, be composed of silicon carbide with sodium silicate as a binder. Such valve type circuit elements have the property of discharging large `currents at nearly constant voltage near their upper voltage limit, but passing only very small currents at lower voltages. These voltage limiting shunts are so related to the circuit being interrupted by the breaker that they Will pass only small currents at normal circuit voltage but at abnormally high voltage, pass suicient additional current to absorb the excess energy associated with the abnormal transient and so limit the voltage to prevent its further rlse.

Referring to Fig. 1, there is illustrated a gasblast type of circuit interrupter generally designated by the reference numeral 1. The interrupter 1 includes an operating mechanism and a gas storage tank enclosed within the housing 8, the latter also serving as a base for supporting an insulating blast tube 9 of tubular form which extends between the reservoir tank and the arc chute I0 employed for interrupting the arc drawn between the stationary contact Il and the movable contact l2. Preferably, opening motion of the C-shaped movable contact l2 is provided by pivotally mounting it at a fixed pivot i3 and employing an operating rod I4 pneumatically operated in desired sequence. The upper end of the operating rod I4 is pivotally connected at I5 to the biiurcated portion I6 of the movable contact l2. Thus downward or opening motion of the operating rod I4 causes counterclockwise rotation of the C-shaped movable contact l2 about its stationary pivot I3 to thereby cause a separation between the movable contact I2 and the stationary contact ll.

Since the line terminals il, It are respectively connected electrically to the stationary contact H and the movable contact i2, an arc is established between the separating contacts ll, I2, within the arc chute l.

Extinction of this arc is readily eilected by a cross-blast of compressed gas, preferably air, passing upwardly through the insulatingr tube Si and transversely across the arc gap between the stationary contact Ii and the movable contact l2. Preferably, a plurality oi slotted spaced insulating plates i9 (Fig. 3) having slots 2D formed therein are provided to permit the arc to be f,

forced laterally by the gas blast against the apices of the slots 2t. The cross-blast of compressed gas causes the arc to be attenuated between the spaced insulating plates i9 to readily effect its extinction. Preferably, such an arc chute construction follows the teachings set forth in United States Patent 2,272,380 which issued February 10, 1942, to Leon R. Ludwig, Herbert L. Rawlins and Benjamin P. Baker, and assigned to the assignee of the instant application.

In accordance with our invention, we employ a probe or auxiliary electrode 2l disposed immediately adjacent to or actually rubbing against the upper side of the movable contact l2, as shown in Fig. 2. In the particular form illustrated, the

gap between the probe 2l and the upper side of the movable contact l2 is 1/4. The probe 2| is electrically connected by a connector 22 to the current limiting valve device, generally designated by the reference numeral 23, and mounted upon ,y

the plate forming the line terminal I'i.

The current limiting valve device 23, in this instance, includes a plurality of non-linear resistance blocks 24 of the type employed in lightning arresters. As mentioned previously, these non-linear resistance blocks 2L'. have the property of discharging large currents at nearly constant voltage near their upper voltage limit, but passing only very small currents at low voltages. To provide a weatherproof construction, a ceramic tube 25 is utilized having at its upper end a metallic cap 293 suitably secured thereto as by cementing at 21.

As the tip of the moving contact i2 moves toward the left, as viewed in Fig. 2, past the probe or auxiliary electrode 2 i the current through the main arc transfers to the current limiting valve device 23 so that the main arc between the contacts il, l2 is extinguished, and only a residual current arc remains to be extinguished, the latter extending between the probe 2i and the tip of the movable contact l2. The blast of compressed gas passing upwardly through the blast tube Si passes partly out oi the opening 23 of the arc chute iii to readily effect extinction of the residual current arc of smaller magnitude.

Thus in Figs. l-3, we have shown a voltage limiting shunt 23 applied to a cross-blast or insulating splitter type of air-blast interrupter.

The shunt is connected between the stationary 4 contact Il of the breaker and an auxiliary electrode 2l at the other end of the arc chute l0 so positioned as to make connection with the moving contact either directly or through a short spark, while the moving contact l2 is within the arc chute l0. The residual current to the shunt 23 is easily interrupted as the tip of the moving contact l2 pulls past the auxiliary electrode 2l to its fully open position outside of the "chute It and separated from it by several inches of air space.

This additional air space is normally designed alone to be able to withstand full circuit voltage with an adequate factor of safety. Even though the shunt 23, so connected, shortcircuits a portion of the contact separation distance in the fully open position, it still enables the breaker to interrupt circuits of higher voltage than could be interrupted Without its presence. This arises because the shunt 23 serves to reduce the maximum overshoot 29 (Fig. 4) of the voltage applied to the interrupting portion of the space by many times. For example, if the space shorted by the shunt 23 constitutes as much as one-half of the total fully open dielectric strength of the breaker, and if the peak voltage 29 applied to this space is limited to one-fourth or less of the peak voltage which would be applied without the shunt 23, then the voltage interrupting ability of the breaker as a whole should be at least doubled.

Such a voltage limiting shunt 23 also serves to protect the breaker and associated insulation from voltage surges occurring during circuit opening but originating in connected apparatus, such as when the interrupter load is or includes an arc furnace. It would also prevent over-voltages due to the cascading effect of restrikes when opening a capacitive circuit. y

We have found that the utilization of such a current limiting valve shunt 23 results in an improvement of 2 to l or better in voltage interrupting ability by using such a voltage limiting shunt.

Fig. 5 illustrates a modification of our invention in which the current limiting valve device 30, in this instance, includes a resistance 3| and a serially connected capacitance 32. The higherthan-normal current produced in this shunt by transient over-voltages results from the higherthan-normal frequency of the transient overvoltage. The operation and the transfer of the main currentto the shunting device 30 isv the same as described heretofore. Again, the residual current arc between the moving contact I2 and the probe 2| is interrupted by the gas blast. Since the current magnitude of the residual current arc is small and of small. leading power factor, the extinction thereof. is readily effected.

The foregoing description of two embodiments of our invention shows that we have improved the interrupting ability of gas-blast circuit interrupters of the cross-blast splitter type by employing a current limiting valve device 23, 30 shunted between the stationary contact Il and the auxiliary electrode or probe 2l. `The shunts 23, 30 serve to have acurrent valve action permitting appreciable ow of current at highvoltage. but reducing it to a very small value as the voltage decreases. The ohmic resistance of the device 2,3 is, therefore, variable and non-linear as a function of applied voltage. Asa result of the decrease in resistance,v the applied. voltage is Aprevented from rising higher than a safe value. Should the recovery voltage continue to rise in magnitude, the effective resistance of the shunt 23 decreases to limit such a rise in applied voltage.

By an application of our invention, we have increased the interrupting ability of cross-blast compressed gas circuit interrupters by a factor of two or more. Further, the connected apparatus and the breaker itself are not subjected pto severe electrical'strain; consequently, the operational life is increased and maintenance costs are considerably reduced.

Although we have shown specic structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. A circuit interrupter including a relatively stationary contact, a movable contact separable from the stationary contact to establish a main current arc, a probe disposed adjacent the path of movement of the movable contact, a resistance, a condenser, means electrically connecting the resistance and condenser in electrical series between the probe and stationary contact, and a residual current arc being established between the probe and the movable contact near the end of the opening operation, the main current arc being extinguished prior to the extinction of the residual current are, and the residual current arc being thereafter extinguished to finally interrupt the electrical circuit.

2. A circuit interrupter of the cross-blast type including a plurality of spaced insulating plates, a relatively stationary contact disposed adjacent one end of the plates, a movable contact separable from the stationary contact to establish a main current arc substantially transversely of the plates, means for forcing a blast of gas across the main current arc laterally thereof to effect the extinction thereof, a conducting probe disposed adjacent the path of movement of the movable contact, a resistance, a capacitance, means electrically connecting the resistance and capacitance in series electrically between the stationary contact and the probe, the current passing through the resistance and capacitance after extinction of the main current arc, and means for forcing a blast of gas against the residual current arc established between the probe and the movable contact to eiect the extinction thereof.

3. A circuit interrupter including means for establishing a main current arc, a resistance and a serially connected condenser, means for electrically connecting the resistance and the serially connected condenser in parallel with the main current arc to more readily effect the extinction of the latter, and means for causing the extinction of the residual current through the resistance and the serially connected condenser following extinction of the main current arc to thereby effect the interruption oi' the circuit.

BENJAMIN P. BAKER. 'II-IOMAS E. BROWNE, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,873,048 Schmidt Aug. 23, 1932 2,049,995 Clerc Aug. 4, 1936 2,052,318 Siegmund Aug. 25, 1936 2,272,380 Ludwig et al. Feb. 10, 1942 2,292,252 Thommen Aug. 4, 1942 2,295,305 Summers Sept. 8, 1942 2,306,240 Wyman Dec. 22, 1942 2,530,939 Browne, Jr Nov. 21, 1950 FOREIGN PATENTS Number Country Date 521,636 Germany Mar. 25, 1931

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