US2530939A - Circuit interrupter with arc extinguishing shunt - Google Patents

Description

Nov. 21, 1950 T. E. BROWNE, JR 2,530,939

cmcun' INTERRUPTER WITH ARC zxwmcuxsnma smmw Filed Sept. 27, 1947 3 Sheets-Sheet 2 WITNESSES: INVENTOR TiakzasEErawnqJ: BY 2? w Anormag Nov. 21', 1950 'r. E. BROWNE, JR

CIRCUIT INTERRUPTER WITH ARC EXTINGUISHING SHUNT Filed Sept. 27, 1947 3 Sheets-Sheet 3 lllllll II III/I II II// INVENTOR T/Iomas EBrawng-Jn QZ'ITORNE WITNESSES:

Patented Nov. 21, 1950 CIRCUIT INTERRUPTER WITH ARC EXTINGUISHIN G SHUNT Thomas E. Browne, Jr., Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 27, 1947, Serial No. 776,513

9 Claims.

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

The general object of my invention is to pro vide an improved arc extinguishing structure in which the power circuit may be interrupted more rapidly and more easily than has been attained heretofore.

Another object is to provide an improved power circuit interrupter having an improved shunting circuit in parallel with the arcing contacts.

Circuit breaker shunts previously proposed or actually used for limiting the rate of rise or ultimate magnitude of voltage restored across the breaker terminals by the circuit at, or just after, the moment of arc extinction have generally consisted of simple resistors and sometimes simple capacitors. A resistance shunt has the advantage of damping the circuit oscillation and thus limiting the restored voltage magnitude by reducing or eliminating the overswing of voltage above the normal peak value of the circuit voltage which otherwise occurs in slightly damped low-power-factor A.-C., or highly inductive D.-C. circuits. Resistance alone has two principal disadvantages: (a) With it, the maximum rate of voltage recovery occurs initially when rate of dielectric recovery is a minimum in types of circuit interrupters when opening short circuits. Resistance shunts are, therefore, comparatively ineffectual in aiding the operation of such interrupters. (b) In order to control the oscillations of high-power circuits, the impedance of the shunt to these oscillating voltages must be fairly low; and such a low impedance, existing also at power frequency (A.-C. circuit) or steady state (D.-C. circuit) for a resistance shunt, results in objectionably large residual current following interruption of the main current. This produces a correspondingly high rate of heating of the resistor and accentuates the difliculty of interrupting the residual current at the final disconnecting break.

Pure capacitance shunts have the advantages of (a) low initial voltage recovery rate and (7)) low power-frequency residual currents (zero for a D.-C. circuit) with negligible heating, but they have the serious disadvantage that they diminish the natural damping of the circuit oscillation, thus generally increasing the amplitude of the voltage overswing. When interrupting low-current. highly inductive circuits, capacitance shunts may also accentuate the tendency of such circuits to produce excessively high voltage iii) swings, or surges, due to premature extinction of the low-current are before its normal current zero moment (alternating current) or before the current has been sufficiently reduced by the interrupter (direct current).

My inventionproposes the use of power circuit interrupter shunts consisting of series-parallel combinations of resistance and. capacitance which will enable the circuit to be more easily interrupted and which avoid the above mentioned difllculties with simpler shunts.

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 diagrammatic view of a circuit setting forth some of the principles of my invention;

Fig. 2 shows two curves illustrating principles of my invention;

Fig. 3 is a curve of the performance of my improved circuit interrupter;

Fig. 4 is a diagrammatic View of a circuit inte rupter embodying my invention and shown in the open circuit position; A

Fig. 5 is a diagrammatic view similar to that of Fig. 4, but showing an extended series-parallel network so that the shunt may be eifective over a wider range of values of the inductance of the circuit;

Fig. 6 is a side elevational View, partially in ertical section, of a compressed gas type of circuit interrupter embodying my invention and shown in the partially open circuit position;

Fig. 7 is a plan view of the interrupter shown in Fig. 6, but the shunting elements assuming a slightly difierent form;

8 is a plan View of the circuit interrupter of Fig. 6 with the shunting elements assuming a still further modified form;

Fig. 9 is a side elevational View of a liquid-poor single bushing type of circuit interrupter embodying my invention; I v

Fig. 10 is an enlarged fragmentary vertical sectional View through the interrupter of Fig. 9, the contacts being shown in the open circuit position;

Fig. 11 is a fragmentary sectional View taken along the line XIXI through the explosion chamber shown in Fig. 10;

Fig. 12 is a sectional View taken substantially along the line XII-XII of Fig. 10, looking in the direction of the arrows; and

Fig. 13 is a sectional view similar to that'of Fig. 12 taken through a modified type of circuit interrupter of the type shown in Fig. 10, but employing the shunting elements in a different arrangement.

Referring to the drawings, and more particularly to Fig. 1 thereof, it will be noted that there is shown a generator of voltage E furnishing power to a circuit of inductance L and having a circuit interrupter in which an arc X is established. The arc X is shunted by a condenser C and a resistance R. The voltage across the arc terminals is designated by e.

It may be readily shown by standard methods of circuit analysis that the differential equation for the arc terminal voltage, e, of Fig. 1 following a momentary extinction of the arc is d e 1 de e E dt RC dt LC LC (1) where E is the steady-state or the peak voltage of the generator (in the A.-C. case, E is assumed to be constant during the time con idered). The complementary function solution of this equation can be written where the ms are determined by the quadratic equation givin 1 1 1 ime m d Lb (4) 1 l 4R C II5 (5) 1 T, R R.

With this critical re ation betwe n R, L and C, the complementary function becomes as shown in t xts on differenti l equations.

Bv standard methods. t e pa t cular integral of Equation 1 turns out to be merely giving the com l te solut on in general form for the case of critical damping:

The arbitrary con tants, A and B, can be evaluated from the initial conditions:

where Ea is the arc voltageand I1 is the are current at which the arc suddenly fails, or goes out, initiating the voltage transient being cone=E and at i=0 sidered. This evaluation yields the complete voltage rise equation:

Assuming both Ea. and I1 to be zero (approximating the A.-C. case) and substituting 1- for the relaxation time, 2R0, leads to the per-unit form of (9):

t t t Fil has been plotted as curve 2 in Fig. 2 for purposes of comparison. The ordinate value 1 indicates the steady-state or the peak value of the generated voltage in Fig. 2.

Fig. 4 shows a circuit interrupter 3 having a pair of arcing contacts 4, 5 and a pair of disconnecting contacts 6, I. The contact 4 is relatively stationary and cooperates with the movable arcing contact 5 to establish an arc indicated by the dotted line 8. The disconnecting contacts 5, l are separated only after interruption of the are 8. They then function to break the residual current are designated by the reference numeral Ila.

During the closing operation, the operating coil 9 is energized by suitable means (not shown), to move the armature l0 upwardly as shown in Fig. 4, at first to cause engagement between the disconnecting contacts 6, I and subsequently to cause reengagement of the arcing contacts 4, 5 thereby to complete the circuit through the load H. The load I I has an inductance L. There is also a small inductance Lo associated with the generator E and the supply leads.

It will be noted that I have provided a shunting circuit about the contacts 4, 1 including a capacitance C1. The capacitance C1 is shunted by an impedance branch including a resistance R and a capacitance C2. Here, the capacitance C1 serves to reduce the natural oscillation frequency of the circuit and es ecially the initial voltage recovery rate. If, in the parallel branch, C2 is considerably larger than C1. its imnedance at the oscillating frequency will be small compared to R and so this branch will have a high power factor at this frequency and will serve as an effective damping means to limit the maximum value of the restored voltage appearing across the arc terminals 4, 5. The damping will be especially efiective if R is of the order of the value of required for critical damping of the L, C, circuit alone. The inductance L0 of the supply circuit is neglected, attention being paid only to the inductance L of the load I I.

This circuit does not yield to mathematical analysis so simply as does that of Figure 1, but an oscillographic study of such a circuit in which load currents are interrupted shows the characteristic voltage recovery [2 to be as shown in Fig. 3, where E is the peak generated voltage. Here, the initial voltage recovery rate, as indicated at [3. zero, and the maximum recovery rate is principally determined by C1 (for a given value of L). With R equal to R0, the overswing ratio can be made as small as one pleases by indefinitely increasing the ratio of C2 to C1. For limited values of em has been found to be a minimum for R slightly larger than Re.

In case a fault, as indicated by the short circuit I4 occurs across the load H necessitating an opening of the circuit interrupter 3, the supply circuit inductance L in combination with C, would require a critical damping resistance Re smaller than that determined for the much larger load inductance L, thus apparently leaving this circuit with relatively little damping. Experience has shown, however, that normal circuit losses plus residual conductanceof the arc path provide effective damping for this small inductance short circuit even without a shunting resistor. Under this condition, also, the capacitor C1 is especially effective in promoting instability of the arc and so in aiding interruption of the shortcircuit.

As indicated, a limitation of the shunting combination of Fig. 4 is that its maximum damping effect occurs at the value of load inductance L for which it has been adjusted and, with changing loads, becomes less (may permit higher peak voltages, em) for values of L very much larger or smaller than this. For extension of the effectiveness of such a shunt over a wider range of values of L, the damping branch RC2 can be replaced by a multi-section repeated series-parallel network such as that illustrated in Fig. 5. Such a network, being a type of low-pass filter, can be designed to vary its effective resistance and series capacitance Values in such a way as substantially to compensate for changes in oscillation frequency due to changes in L. The circuit of Fig. 5 was found (with to give satisfactory damping for variations in L by a factor of 100 or more. A different relation between successive resistance and capacitance values in the damping network might give more efficient utilization of the circuit elements.

With the foregoing principles in mind, I shall now describe some applications of my invention as applied to high voltage circuit interrupters of both the compressed gas form and the liquid break form. Referring to Fig. 6, the reference numeral 56 designates a grounded base upon which is mounted a high voltage compressed air form of circuit interrupter generally designated by the reference character l1, and including an interrupting chamber l8 serially connected with disconnect contact structure ii), the latter being shown in the closed position. The chamber i8 is formed by a cylinder 20 preferably formed of a vitreous insulating material. Interiorly of the chamber I8 is a movable contact 2i separable downwardly away from a stationary orifice shaped contact 22 to draw an are 23. Suitable means, not shown, may be provided to admit compressed gas from a source of compressed fluid upwardly through the supporting column 24 and adjacent the are 23 as indicated by the arrows 25.

The gas passes out of the interrupter I! through the hollow stationary contact 22.

A bracket 21 of plate-like configuration juts laterally from a casting 28 which fastens the supporting column 24 and the vitreous cylinder 20 together. The bracket 2'! supports the shunting circuit including the condenser C1 and C2. The upper end of the condenser C1 is connected electrically to the stationary contact 22 by a conducting strap 29. In parallel with the condenser C1 is the parallel impedance branch including the condenser C2 and the resistance R. Preferably, the resistance R assumes the form of a tube 30, the composition of which is such as to provide the desired resistance.

Following extinction of the are 23, the disconnect contact structure IE! is operated to cause opening of the movable disconnect contact 3| upwardly to the position shown in dotted lines 32. Thus there is a considerable gap provided between the movable disconnect contact 32 and the stationary disconnect contact 33, the latter connecting with the line terminal 34. The other line terminal 35 of the circuit interrupter i 'I is electrically connected to the stationary contact 22. It will be noted that the arcing contacts 22. 2| of the circuit interrupter I! have in parallel therewith a shunting circuit such as shown in Figure 4, and the theory of operation is the same as that previously described in connection with Fig. 4.

Referring now to Fig. 7, it will be observed that I have shown a plan view of a circuit interrupter of the type described in Fig. 6 with the exception that the impedance branch which parallels the capacitance C1 (which in Fig. 6 includes the elements R and C2) in Fig. 7 consists of five parallel branches symmetrically positioned about the capacitance C1. Each of these five parallel branches around C1 has A; the admittance of the parallel branch R and C2 of Fig. 6. Thus, the electrical efiect is the same and the only difference is a different form of shunting path about the capacitance C1. The interrupting chamber I8 and the disconnect contact structure i9 is the same as was described in Fig. 6.

Referring to Fig. 8, it will be noted that I have shown a circuit interrupter of the type set forth in Figs. 6 and '7, but the shunting circuit about the capacitance C1 assumes the form as set forth i Fig. 5, where the damping branch RC2 is replaced by a multisection repeated series-parallel network such as that illustrated in Fig. 5. The theory of operation is the same as that described in connection with Fig. 5.

Fig. 9 designates a liquid-poor single bushing type of circuit interrupter, designated by the reference numeral 3?. Certain constructional features thereof are set forth in United States patent application filed May 19, 1945, Serial No. 594,634, now Patent No. 2,479,381, by Leon R. Ludwig and Benjamin P. Baker and assigned to the assignee of the instant application.

It will be noted that a base 38 supports a grounded framework 39 at the upper end of which is supported a circuit interrupter of the single bushing type. Fig, 10 shows more clearly the internal construction of the interrupter. Referring to Fig. 10, it will be observed that the grounded framework 26 supports a single terminal bushing 4| at the lower end of which is secured an arcing chamber generally designated by the reference numeral 42. A stationary contact 43 is disposed at the upper end of the arcing chamber 42.

Cooperable with the stationary contact is is a movable contact l4 shown in the open circ .it position in Fig. 10. A compression spring l5 biases the contact 2 downwardly in the circuit opening direction. A movable disconnect contact 46 makes abutting engagement with the lower end ll of the movable contact during the closing stroke, to carry the latter upwardly against the biasing action exerted by the compression spring 45 until the movable contact makes abutting engagement with the stationary contact iii. The movable disconnect contact 65 is rod-shaped in configuration and is guided by upstanding brackets 43. The brackets are mounted adjacent the lower end 59 oi the cylindrically shaped housing structure 56.

Fig. 11 shows the internal structure of the arcing chamber :2. It will be noted that a slot El is provided lon itudinally of the arc which is established by the contacts cs. Arc extinguishing liquid, such as circuit breaker oil fills the housing to the level 55, as shown in Fig. 10. Thus, the establishment of an arc between the contacts 23, dd within the explosion chamber 32 during the opening operation established ressure therein to cause blast of fiuid laterally or" the are 52 and out of the arcing chamber through the lateral slot 5!. The ac 52 is hence interrupted by a turbulent blast of oil out of the arcing chamber 42.

Fig. 12 is a fragmentary plan sectional view through Fig. to indicate the shunting circuit arrangement utilised in Fig. 10. It will be noted that a connector 55 electrically connects the stationary contact 33 with the capacitance Cl. Shunting the capacitance C1 are four parallel impedance branches collectively forming electrically a single impec'ance branch paralleling the capacitance C1. Each of the other capacitances 56 has a capacitance value of and the resistance tubes El" have a resistance value of 4R. In other words, the shunting circuit assumes the same form electrically as that shown in Fig. l. The use of four capacitances collectively totalling a value equal to C: simplifies the mounting arrangement and permits their symmetrical mounting around one half of the periphery of the arcing chamber 22 on a support plate 53, the latter secured by one or more bolts 59 to the lower end of the extinguishing chamber 42. A strap connector 69 electrically connects the support plate 58 to the movable contact M.

Fig. 13 is a view similar to Fig. 12, but shows a modified type of shunting arrangement which assumes the form of that already described in connection with Fig. 5. In other Words, Fig. 13 shows the interrupter of Fig. 10 with the exception that the damping branch RC2 is replaced by a multi-section repeated series-parallel network such as that illustrated in Fig. 5.

Actual interruption tests with an air-blast circuit interrupter shunted by two condensers and a resistor connected as in Figure 4 have demonstrated the eliectiveness of such a shunt in substantially reducing the air pressure required for interruption over a 40 to 1 range of currentliiniting inductances. Tests were made at 50 to 4,006 amperes at 13,800 and 6,900 volts, 60 cycles. The shunt was adjusted for an inductance value near the maximum since it was found, as mentioned above, that unavoidable losses in the practical test circuit alone caused suflicient damping at the lower inductance values to prevent large voltage overswings.

These shunts combine the desirable character istics: (a) Low residual steady-state or power frequency currents and losses, (1)) minimum rate of voltage rise initially, (c) small voltage overswing, (d) possibility of automatic adjustment for a wide range of circuit conditions, (e) applicability to either A.-C. or D.-C. circuit interrupters.

Although I have shown and described specific 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 by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A circuit interrupter including means establishing an arc, a capacitor connected directly in parallel with said means, and an impedance branch shunting the capacitor including a serially related resistance and a capacitor of greater capacitance than the first :iaid capacitor.

2. Are extinguishing means including contact means for establishing an arc, a capacitor connected directly in shunt with the contact means, and a shunting impedance branch also across the contact means including a serially related resistor and a capacitor of greater capacitance than the first-mentioned capacitor.

3. Circuit interrupting means for interrupting a load having an inductance L including contact means for establishing an arc, a capacitance Cl connected directly in parallel with the contact means, an impedance branch including a resistor R and a serially related capacitance C2 having a higher value capacitance than the first said capacitance in shunt with the capacitance C1, the resistor R having a value of the order of magnitude of 4. A circuit interrupter including means establishing an arc, a capacitor connected directly in parallel with said means, an impedance branch shunting the capacitor including a serially related resistance and a capacitance having a greater capacitance than the first said capacitor, and means for interrupting the residual current through the interrupter.

5. Arc estinguishing means including contact means for establishing an are, a capacitor connected directly in shunt with the contact means, a shunting impedance branch also across the contact means including a serially related resistor and a capacitor having a greater capacitance than the first-mentioned capacitor, and means for interrupting the residual current through the arc extinguishing means.

6. A circuit breaker including a pair of separable arcing contacts, a capacitor connected directly in shunt with the arcing contacts, a plurality of cascade connected impedance branches in shunt with the capacitor, and each impedance branch including a serially related resistor and capacitor shunting the preceding capacitor.

'7. A circuit b 'eaker including a pair of separable arcing contacts and a serially related pair of separable disconnect contacts, a capacitor connected directly in shunt with the arcing contacts, a plurality of cascade connected impedance branches in shunt with the capacitor, each impedance branch including a serially related resister and capacitor shunting the preceding capacitor, and the disconnect contacts opening after the arcing contacts to interrupt the residual current through the circuit breaker.

8. A circuit interrupter including an arcing chamber, means for establishing an are within the arcing chamber, means for subjecting the arc to a blast of fluid to facilitate its extinction, a capacitor connected directly in parallel with the arc, an impedance branch shunting the capacitor including a serially related resistance and a capacitance having a greater capacitance than the first said capacitor, and disconnect means for interrupting the residual current are through the capacitor and shunting impedance branch.

9. A circuit interrupter of the fluid blast type including an arcing chamber, means for establishing an are within the arcing chamber, means for subjecting the arc to a blast of fluid to facilitate its extinction, a capacitor connected directthe preceding capacitor, and disconnect means for interrupting the residual current.

THOMAS E. BROWNE, JR.

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

UNITED STATES PATENTS ly in parallel with the arc, a plurality of cascade 20 connected impedance branches in shunt with the capacitor, each impedance branch including a serially related resistor and capacitor shunting Number Name Date Kelly Jan. 12, 1904 Weaver Nov. 10, 1931 Curtis Oct. 10, 1933 Cain Aug. 13, 1935 Thommen Apr. 19, 1942 Thommen Aug. 4, 1942 Thommen Dec. 7, 1943 Thommen Feb. 1, 1944 FOREIGN PATENTS Country Date Great Britain Mar. 29, 1934

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