US3147356A - Circuits for switches having series connected interrupter sections - Google Patents

Description

Sept. 1, 1964 E. L. LUEHRING 3,147,356 CIRCUITS FOR SWITCHES HAVING SERIES CONNECTED INTERRUPTER SECTIONS Filed March 15, 1961 I E 24 (l6 5 25 39 K 35% (2oommf)T -i-' 120 i O 6 ll (rem 538 31 I I4'../ 33 1 I I V :l 36 i II; ;,.(2Ommf) (ZOOmmf) i LZ l INVENTOR. ELMER L. LUEHRING ATTORN EY United States Patent "ce 3,147,356 CIRCUITS FOR SWITCHES HAVING SERIES (IONNECTED WTERRUPTER SECTIGNS Elmer L. Luehring, Cleveland, Ohio, assignor to .loslyn Manufacturing and Supply (10., Chicago, 111., a corporation of Illinois Filed Mar. 15, 1961, Ser. No. 95,961 2 Claims. (Cl. 200-145) The present invention relates to high voltage switches and has particular significance in connection with high voltage power line switching apparatus having series connected interrupters each of the type enclosed in vacuum or immersed in a fluid other than air. As already explained in US. Patents 2,915,611 and 2,955,181, the voltages, and charging and interrupting currents, of present day transmission lines, transformers and capacitors, have been so large that as many as eight vacuum interrupters are arranged mechanically to operate together while electrically in series. In connection with such apparatus a difliculty in the past has been inability of the interrupters to divide the total voltage equally between them. Also the series arrangement of interrupters has caused transient overvoltages whereby the recovery voltage of one switch may be many times the voltage applied to all. For these reasons the individual interrupters had had to have such a high voltage rating that the total cost of a complete installation has been incompatible with the economics of modern practices, and even so any one of the interrupters is apt to be subject to ruinous arcing and damage.

It is an object of the present invention to provide simple and inexpensive means for overcoming the above mentioned difficulties.

Another object is to provide for series connected interrupters means which will afford linear voltage distribution thereover.

Other objects and advantages will become apparent and the invention may be betterunderstood from consideration of the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a side view in part section showing a modular incapsulated vacuum interrupter provided with circuitry according to the invention and attached to the top of a like unit below and to tandem interrupter operation mechanism above;

. FIG. 2 is a simplified schematic diagram provided for the purpose of explaining the operation of the present invention.

Although but one interrupter unit is shown in its entirety in FIG. 1, it should be understood that a number of like units are arranged to be mechanically operated in tandem. When an initial signal is sent by some means (not shown) to actuate a top mounted apparatus Which may comprise a toggle (not shown herein but one example of which is illustrated and described in the above mentioned Patent 2,955,181) this operates a main pull rod 10, draw bar 11, insulating material operating rods 12, and cross bars 13 which are provided, one for each unit, to eventually operate a mobile contact rod 14 of the respective interrupter. Each of the interrupter units may comprise a vacuumized glass envelope 15 having metal end caps 16, 17. The movable contact rod 14 is electrically attached as through a metallic bellows with end cap 16 and cooperates with a stationary contact rod 18 which is electrically in circuit with the end cap 17. The movable contact 14 is in circuit with a flexible electrical connection shown diagrammatically at 19 which, in turn, is in circuit with an outside line indicated diagrammatically as L1, while the bottom cap 17 of the unit shown in section is connected through the flexible connection 2%) to be in circuit with the movable rod 14' of 3,147,356 Patented Sept. 1, 1964 the next interrupter below, and so on. Each interrupter need not necessarily be of vacuum type since the enclosed contacts might be immersed in an inert gas or in a liquid such as oil, and each of the originally enclosed interrupters may be separately incapsulated in its own somewhat resilient material permanent shockproof container comprising a cellular foam 21 extending around the envelope and within an annular housing 22 as described and claimed in Patent 2,915,611.

In accordance with the illustrated embodiment of the present invention, see FIG. 2, each contact pair 14-18, 14/48 is deliberately provided with a shunt circuit comprising a series arranged resistor 24 and capacitor 25 (FIG. 2) or capacitors (FIG. 1).

FIG. 2, for simplicity, shows only a single pair of interrupters (14-18 and 14'18') but the principles are equally applicable in cases where there are more than two such switch sections in series. As shown, a high voltage source 27 feeds line L1 and in turn the series connection of the interrupters cooperable with a return line L2 to supply a load as indicated diagrammatically at 28, 29.

Forgetting for the moment the effect of the provided resistors 24 and capacitors 25 there is inherently, as shown in dotted lines, a capacitance 30 between the end caps 16, 17, which capacitance has one value when the contacts are open and another when the contacts are closed, and there is an inherent capacitance 31 between the end caps 16', 17' of the other interrupter. These are stray capacitances dependent in large measure on the dimension of the end caps and parts of associate potential, and there are other stray capacitances as illustrated at 32 and 33 and between the end caps and ground which, of course, presents a very large surface which is closest to the lowermost end caps. Inherent also are leakage resistances, as indicated at 35 representing the resistance between the terminals of the top switch, and at 36 for the resistance between the top terminal of the bottom switch and over the insulation to ground.

In the past it has been found almost impossible to cal culate the effect of these leakage resistances and capacitances, because the capacitive reactance is one thing at 60 cycles and quite another when lightning strikes so that there are very high frequency components (up to 2 megacycles) and the capacitance predominates. But supposing that the sum total of the paralleled capacitance of 30 and 32 is l0 1O- farads (10 mini.) and, because so much closer to ground, the total of the leakage capacitance about switch 14', 18 and to ground is 20x10- farads. Then there is difference between the two values, and, there is going to be a much greater voltage across one unit than across the other and, because it is difiicult to make all the interrupters operate at precisely the same moment, the situation is made even worse if one of the set of contacts 14-18 happens to be open, While the other is closed or arcing.

I have found that it is not enough to simply place one capacitor (25) across each set of interrupter contacts to introduce such a dominant influence that each such switch has a voltage across itself less dependent on the inherent characteristics of the switch, its distance from ground, and the operative state of the switch (whether open or closed, arcing or not). That is, it is not enough to just use capacitors (25) each, say of 200 mmf., placed across one interrupter pair on the theory that then the 16-17 total capacitance becomes 210 mmf. while the 16'-17' total capacitance is only 220 mmh, a difference of less than 5% rather than the prior 100%.

The present invention has its basis in part on the realization that the straight cont-act stems have not only an inherent resistance (33 in FIG. 2) but also an inherent inductance (symbolized at 39 in FIG. 2) so that regardless of whether or not capacitance (such as 25) is added (to the inherent capacitance), for each interrupter a tank circuit is set up which achieves resonance at a certain frequency which not only causes radio noise but causes the voltage across the particular switch contacts to often rise to a value higher than the total voltage applied across all the switches in series. This will cause a deleterious spark over, around the outside of the enclosing bottle even if the switch is closed, or open and carrying current through an are. 7

For some particular switches used, which switches were equipped with 12" diameter end caps, and cylindrical electrode type contacts 1" in diameter (0.785 sq. in. in contact area) with a A" spacing between electrodes when open, and which were 18" length overall (from outer end of one cap to outer end of the other), even with added shunt capacitors (25 but without 24) selected at 200 mmf. the resonant frequency for the tank circuit was about 30X 10 cycles per sec., while 0.7 of the voltage at resonance was found at two frequencies differing by 1.5 10 cycles.

As is well known these frequencies become f and f -f in the equation for Q, or Figure of Merit, where From such a Q it is possible to obtain a desirable value for a series resistor (24) once the need thereof is recog nized.

It should be noted that there were resonant circuits even before any swamping capacitor (25) was introduced. But the important thing is recognition ofthe fact that there are resonant circuits, that they permit of the calculation of a Q and, therefore, of the calculation of desired series resistance for a swamping capacitor in order to damp out resonance effects, or in other words to lower the Q. For some applications it has been found that desirable results are achieved when each interrupter has in shunt about its contacts the series circuit of a capacitor 25 of 200 mmf. and a resistor 24 of 16 ohms, for this lowers the'Q, cuts radio noise, and prevents flashovers, by making the voltage distribution across each switch less dependent upon its inherentcharacteristics, distance from ground, and Whether the switch is open or closed.

Instead of the single 16 ohm resistance 24 and single capacitance as illustrated in FIG. 2 for any one interrupter, it may be desirable to use, for example, for each interrupter three shunt circuits each having one resistance of 48 ohms and in series therewith an appropriate portion of the swamping capacitance.

It may be that the higher the frequency the less the relative effect of the leakage resistance, but nevertheless, even with lightning strokes, intentional introduction of both capacitance and resistance, together in series with each other and in shunt across the interrupter contacts of each pair, lowers theQ, and cuts down on overvoltage across any one interrupter while even for 60 cycles the voltage is fairly evenly divided, for example, 51% and 49%, instead of the prior 66% and 33%. This gives better voltage distribution between interrupters and allows the recovery voltage of each one to be substantially less than the voltage applied to all. As one interrupter stops arcing, its recovery voltage (that is the voltage trying to re-establish the arc) becomes a function of the circuit parameters of a desired circuit instead of a function of the parameters of an undesired tank circuit, open circuit voltages are more nearly evenly divided, and undesirable closed circuit overvoltages are avoided.

While I have illustrated and described a particular embodiment, various modifications may obviously be made without departing from the true spirit and scope of the invention whichis intended to bedefined only by the accompanying claims taken with all reasonable equivalents.

I claim:

1. In switch mechanism of the type having plural series connected interrupter contact pairs, a plurality of voltage dividing capacitors at least equal in number to the number of contact pairs and respectively arranged in shunt around the various contact pairs and provided additional to the inherent stray capacitance of the respective contact pairs, and .plural resistors at least equal innumber to the number of contact ,pairs and provided additional to inherent leakage resistance and respectively arranged at least one separately and permanently in series with each unit of voltage dividing capacitors with each such resistance capacitance circuit in sunt around a respective contact pan.

2. The combination of claim 1 further characterized by the resistors having ohmic values selected to lower the Q of each capacitor and contact pair circuit when the contacts of the respective'pair are closed.

References Cited in-the file of this patent UNITED STATES PATENTS 2,340,827 Thommen Feb. 1, 1944 FOREIGN PATENTS 689,973 Great Britain Apr. 8, 1953 1,052,503 Germany Mar. 12, 1959 1,064,134 Germany Aug. 27, 1959

Claims (1)

1. IN SWITCH MECHANISM OF THE TYPE HAVING PLURAL SERIES CONNECTED INTERRUPTER CONTACT PAIRS, A PLURALITY OF VOLTAGE DIVIDING CAPACITORS AT LEAST EQUAL IN NUMBER TO THE NUMBER OF CONTACT PAIRS AND RESPECTIVELY ARRANGED IN SHUNT AROUND THE VARIOUS CONTACT PAIRS AND PROVIDED ADDITIONAL TO THE INHERENT STRAY CAPACITANCE OF THE RESPECTIVE CONTACT PAIRS, AND PLURAL RESISTORS AT LEAST EQUAL IN NUMBER TO THE NUMBER OF CONTACT PAIRS AND PROVIDED ADDITIONAL TO INHERENT LEAKAGE RESISTANCE AND RESPECTIVELY ARRANGED AT LEAST ONE SEPARATELY AND PERMANENTLY IN SERIES WITH EACH UNIT OF VOLTAGE DIVIDING CAPACITORS WITH EACH SUCH RESISTANCE

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