US3198986A - High voltage switching apparatus - Google Patents

Description

Aug. 3, 1965 E. L. LUEHRING ETAL 3,198,986

men VOLTAGE swncnxue APPARATUS Filed July 12, 1962 1 (26 127 i I I i 33 CG 3?) CG 33 CG Q4 Q3 Q2 GI 04 Q3 Q2 Ql Q4 Q3 Q2 0! ".35 2| 1: 1; 22 1:12-23 24/CZ'I DA B J FIG-3 H INVENTORS ELMER L. LUEHRING JOSEPH D. HOFFMAN ATTORNEY United States Patent 0 HllGlll VULTAGE fiWlTCHlNG APPARATUS Elmer L. Luehring, Cleveland Heights, and Joseph D.

l-lofirnan, Shaker lileights, Ohio, assignors to .loslyn and Supply (30., a corporation of Illinois, High- Voltage Equipment Company Division, Cleveland, Ohio Filed .luly 112, i962, Ser. No. 209,339 7 Claims. (ail. 31711) The present invention relates to high voltage switches and is known to have particular significance in connection with mechanically tandem operation of electrically series connected switches capable of interrupting alternating current at a point other than at normal current zero.

While only a single phase operation is described and only single phase schematics are shown for simplicity, in a complete installation the arrangement may be multiplied to provide for plural phases.

Alternating current interrupters that have natural arc instabilities typically do not extinguish at normal current zeros in alternating current systems. The stability of an arc in such a device is dependent upon many things including: work function of cathode electrode material; vapor pressure of cathode electrode; melting point of cathode electrode; rate of rise of recovery voltage by which is meant the voltage trying to reestablish the arcing condition after extinction; instantaneous distance of contact separation; maintenance of constant direction of electron fiow during arc extinction; temperature of cathode electrode; relative value of system current, etc. While it is true that during the period of time that current is increasing an interrupter might not display such instability as a consequence of contact (electrode) separation increasing more slowly than the system current, even so no exception is evident with low maximum value of current, because of the relatively low rate of rise of current where there is such a low maximum.

Heretofore for some applications the problem of voltage exceeding the withstand ability of individual interrupter switches has not been solved by using series connected interrupter contact pairs. The interrupters are naturally unstable and can be used in series only if the product of system surge impedance (ohms) and electrode maximum instantaneous arc instability (amperes) is less than the voltage withstand ability of a single pair of interrupter electrodes when the voltage functions of these two quantities are compared instant by instant and added to steady state system recovery voltages. Thus the usefulness of interrupters has been limited to switching at system voltages where the transient recovery voltage does not exceed the recovery ability of a single pair of contact electrodes.

Stated in another way, enclosed against ambient switches (such as vacuum switches) can be connected electrically in series and mechanically synchronized as far as possible but even if all could be operated to have the same contact separation at the same instant (which i not the case) even so they would not all approach arc instability together. One would have its arc go out first, and this would induce a high voltage across the high impedance of the inherent capacity of that particular switch, hence raising the withstand voltage rating required of that particular switch (and of all the switches for that matter since there is usually no way of knowing which one will reach arc instability first).

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

Another object of the present invention is to provide more economical switching, as regards first cost and maintenance factors.

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Broadly stated, in accordance with one aspect of the invention each of one or more naturally unstable switches is shunted by a circuit comprising resistance and a number of small air gaps in series. The gaps have normally poor voltage distribution but, because they are arranged in series, self induction causes a cascading are to elongate and the recovery ability of these gaps is achieved by the improvement of voltage distribution in the gap system as a result of the presence of arc products between the gaps after extinction at a normal system current Zero.

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

FIG. 1 is a simplified schematic diagram showing the invention applied to series connected interrupter switches;

FIG. 2 is a graph showing voltage and current relationships during operation of apparatus such as that shown in FIG. 1;

FIG. 3 shows a modification.

For any interrupter switch, as Well as for any arrangement of series connected interrupters, the limit imposed by the single set, or series sets, of contact electrodes is real because (1) the arc instability characteristic of any set of electrodes i a statistical variable, and (2) the impedance of an interrupter is highest following a natural instability extinction as opposed to an outside influence causng current reduction or elimination.

It is dilllcult, and probably impossible, to eliminate arc instability by choice of electrode materials. Any solution of the problem tated is further complicated because any statistically based insurance must be almost instantaneously compensatory. In some applications, the problem can be solved by reducing the surge impedance of t e load to be disconnected, but with many other applications it is not economical to handle the problem in this manner and it i for such applications that the presently described arrangements are useful.

Referring now to FIG. 1, a high voltage source 10 is shown supplying a shunt reactor 11 through a plurality of switches, B3431, connected in series electrically and mechanically connected to operate substantially together as indicated by the broken lines 12. As described in US. Patent 2,955,181, there may be a driver-actuator switch DA for taking into and out of the circuit the plurality of series connected switches which may be enclosed against ambient, being, for example, vacuum switches, and thought of as bottles. As disclosed and claimed in the above mentioned patent, arrangements can be made so that, during opening, the bottle contacts open first, and then the driver-actuator DA opens, so as to keep the bottle contacts out of the circuit during a later closing sequence through other switches not shown in the present case drawings but fully illustrated and described in the above mentioned patent.

As shown in dashed lines in FIG. 1, there are inherent capacitances 21-24 from the switch contacts to ground, and inherent capacitances 252'7 around the contact pairs of the respective switches. These are stray capacitances dependent in large measure on the dimensions of the switch contacts and other parts of associate potential and each of them has one value when the associate switch contacts are closed and a quite different value when the contacts are open. There is some leakage resistance as well, but this need not be considered in connection with the explanation of the present invention.

When the present invention is applied to more than one interrupter switch in series, it is essential that something more than the inherent stray capacitances (shown in dashed lines) he provided in order to properly divide the voltage drop across the respective switch contact pairs. To overcome this there is shown in FIG. 1 for each switch (Bl-B3) a shunt circuit of a series connected resistance 31 and capacitance 32. This divides the voltage more evenly than would the inherent capacitances particularly when, as is often the case, one interrupter is physically closer to ground than the others (for example, see the arrangement in the above mentioned Patent 2,955,181

Suppose Bl-BS all start to open together drawing three arcs one of which wizl almost certainly go .out first and allow the induction of a high voltage across the high impedance of the inherent distributed capacity (25, 26 or 27), as modified by one pair of 31-32, of that particular switch. Then the switch has to withstand more voltage after having broken the arc than, with or Without the voltage dividing function of 31432, it had to stand before it broke the arc. In order to overcome this I provide a gap system that will break down electrically before the interrupter switch is damaged by over-voltage and then will interrupt the current flowing through it more nearly at a normal current zero. This can be a system that can withstand more voltage after having contained an arc than it could before it contained the arc. The gap system is put in shunt across each swivel and, in FIG. 1, each such gap system comprises a plurality of series connected quench gaps Ql-Q t, a physically relatively remote therefrom series calibrating gap CG and a series resistor 33. Use of the calibrating gap is not essential, as will later become apparent in the discussion in connection with FIG. 2, but if it is used its gap is sufiiciently small so that as soon as one set of interrupter contacts (Bil, B2, or B3) has its arc reach instability and sufficient voltage develops across the contacts, the associate calibrating gap CG will spark over, and, if the calibrating gap is used, the quench gaps are even smaller, at least as to the space apart of the electrodes of each, and in series with each gap system there is included a current limiting impedence. This might be a capacitor but use of a pure resistance (33) is advantageous economically. Since the arc instability is evident below a certain instantaneous value of current, the value of each resistance 33 to be used can be determined by the formula:

where R=value of resistance to be used,

E =peak withstand voltage of the unstable interrupter contact system, and

I =maximum instantaneous current instability level of the unstable interrupter, as determined by test.

Obviously, then, the gap system breakdown voltage must be less than E but as many units of this series parallel system (of interrupter switches with shunted circuit of resistance and multi-gaps in series) can be placed in series as required to accommodate insulation requirements so long as the voltage distribution of the units is equalized (as by the resistance capacitor shunts).

The quench gaps, in any event, are suh'iciently small so that as the associate interrupter contact pair has its arc reach instability, the quench gaps will sequentially spark over shifting current to a new sinusoidal phase representing load plus the particular series resistance 33.

This may be more clear from consideration of FIG. 2 where V indicates the wave shape of terminal voltage at the source 10. Assuming DA and 133-331 in FIG. 1 all closed, 1 represents a first value of current assumed 90 lagging because of the inductive load 11. Bl-B3 start to open drawing arcs and as the first one of these arcs is extinguished at a time t the associate one of the resistances 33 completing a circuit through all of the associate spark gaps shifts the phase of the current to nearer unity power factor as indicated at 1 At a time 1 a sec- 0nd interrupter switch arc is interrupted shifting current to an even more in-phase (and lower amplitude) wave I at i the third interrupter arc goes outshifting the current to 1 (which is almost the in-phase condition desired) and ultimately arcing stops across the spark gaps and the current goes to zero so far as the quench gaps are concerned. Although there may be an infinitesimally small continued current through the series circuits of resistances 31 and capacitors 32 this is readily interrupted by the switch DA when it later opens.

The use of two or more like dimensioned gaps in shunt across each relevant pair of interrupter contacts aids in establishing the proper characteristics having in mind that not only must any included spark gap spark over on a certain voltage but must, at other times during operation, be able to withstand some other voltage value without sparking over. As has been known heretofore, ten gaps of 1" though connected in series do not operate the same as one gap of 10'. Because of charging currents in the line and hardware one will spark over before the others even though the total stack voltage is less than ten times the spark over voltage of any individual gap. Thereafter the voltage across every other gap in the series circuit increases and the effect cascades until all have broken down.

Whether or not a calibrating gap is included in the circuit, in accordance with the invention there are at least two (and preferably three or more, and for a single interrupter we have with good results used as many in series as forty) quench gaps by which is means plural gaps having substantially the same dimensions. Thus two or more gaps take the place of one according to the invention and this enables gap spark over at a voltage which is low enough so that it will not damage the interrupter switch contacts while on transient recovery, after ultimate eX- tinguishment of the are at all sprak gaps, none of the spark gaps will spark over for though there will be higher instantaneous total voltage it is more evenly distributed (1) over the gap systems if there are more than one, and (2) over the gaps of each system.

There is thus provided an arrangement of the class described capable of meeting the objects above set forth. Each system of plural gaps can withstand more voltage after having contained an arc than before it contained the arc. Such a system has natural arc stability, and a low rate of rise of dielectric strength. As many units of this series parallel system (of interrupter contacts shunted by series circuit of resistance and plural gaps) can be placed in series as required to accommodate insulation requirements providing only that if there is more than one interrupter switch, the voltage distribution of the units is equalized to coordinate with the requirements (as by use of shunt paths of resistance 31 and capacitance 32).

FIG. 3 shows another way of taking advantage of the present invention comprising small substantially identical gaps in series. Here there is no calibrating gap but there are plural quench gaps Q in series with resistance 33 with this series circuit in shunt with a single interrupter contact B. During operation, as B opens self induction causes a cascading arc to elongate across the quench gaps and as the gap arc is extinguished there is an improvement of voltage distribution in gap system resuiting from are products which prevents re-establishment of the are after a normal current zero.

With arrangements according to the invention voltage and current can more readily reach zero together and in such manner as to minimize the transient recovery voltage. Less expensive equipment can be used than heretofore and there is no longer the possibility of subjecting parts to two times peak voltage but suddenly attempting to open a circuit to an inductive reactance load.

While I have illustrated and described particular embodiments, various modifications may obviously be made without departing from the true spirit and scope of the invention which is intended to be defined only by the appended claims taken with all reasonable equivalents.

We claim:

1. For use with high voltage switching equipment comprising a plurality of n vacuum interrupter units electrically in series with one another and mechanically connected to operate substantially together,

a plurality of n deliberately provided circuits each comprising a path in shunt around a dilferent one of said interrupters for substantially dividing voltage equally over the interrupters,

and an additional plurality of n circuits each comprising a path in shunt around a diflierent one of said interrupters with said last mentioned paths each comprising the series circuit of a current limiting means and a plurality of at least two quench gaps.

2. The combination of claim 1 further characterized by the current limiting means in the second mentioned plural circuits comprising resistors.

3. The combination of claim 1 further characterized by the second mentioned plural circuits each having at least three quench gaps in series.

4. The combination of claim 1 further characterized by the second mentioned plural circuits each having at least three quench gaps and one gap of larger dimension than each of said qunch gaps, all in series with the current limiting means of the particular second mentioned plural circuit.

5. In a circuit a first interrupter means and in shunt therewith the series circuit combination of a second interrupter means and a resistance whose value is not more than R=WI when E peak withstand voltage of said first interrupter means and I=maximum instantaneous current instability level of said first interrupter means as determined by test.

6. Plural series connected circuits each being the circuit of claim 5.

. 7. Plural series connected circuits as in claim 6 further characterized by each first interrupter means comprising contacts operating in a vacuum.

References Cited by the Examiner FOREIGN PATENTS 27,138 7/16 Norway. 588,204 11/33 Germany.

SAMUEL BERNSTEIN, Primary Examiner.

Claims (1)

1. FOR USE WITH HIGH VOLTAGE SWITCHING EQUIPMENT COMPRISING A PLURALITY OF "N" VACUUM INTERRUPTER UNITS ELECTRICALLY IN SERIES WITH ONE ANOTHER AND MECHANICALLY CONNECTED TO OPERATE SUBSTANTIALLY TOGETHER, A PLURALITY OF "N" DELIBERATELY PROVIDED CIRCUITS EACH COMPRISING A PATH IN SHUNT AROUND A DIFFERENT ONE OF SAID INTERRUPTERS FOR SUBSTANTIALLY DIVIDING VOLTAGE EQUALLY OVER THE INTERRUPTERS, AND AN ADDITIONAL PLURALITY OF "N" CIRCUITS EACH COMPRISING A PATH IN SHUNT AROUND A DIFFERENT ONE OF SAID INTERRUPTERS WITH SAID LAST MENTIONED PATHS EACH COMPRISING THE SERIES CIRCUIT OF A CURRENT LIMITING MEANS AND A PLURALITY OF AT LEAST TWO QUENCH GAPS.

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