US2094361A

US2094361A - High voltage direct current contactor

Info

Publication number: US2094361A
Application number: US31745A
Authority: US
Inventors: Lee Reuben
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1935-07-16
Filing date: 1935-07-16
Publication date: 1937-09-28
Anticipated expiration: 1954-09-28

Description

Sept. 28, 1937. R. LEE

HIGH VOLTAGE DIRECT CURRENT CONTACTOR Filed July 16, 1935 A 6 8 F. T 6 m 9 a; E flu y a v E M V 4/ B M V a. V U 2 V 2 A A E Z 0 0 MBA Q a w a 7W MM p 1 WITNESSES:

INVENTOR Rel/be)? Lee.

ATTORN Patented Sept. 28, 1937 UNITED STATES PATENT OFFICE HIGH VOLTAGE DIRECT CURRENT CONTACTOR Vania Application July 16, 1935, Serial No. 31,745

3 Claims.

circuit without interrupting or cutting in on the operation of the other transmitters.

According to prior practice, a plurality oftransmitters derive their high voltage direct cur- 5 rent potentials from a common source of low frequency alternating current, the voltage of the alternating current system or source being stepped up by means of a transformer to the desired high voltage and subsequently rectified and filtered and applied to the transmitters. In switching one or the other of a plurality of transmitters into or out of the supply circuit, it is necessary to open the supply circuit on the low voltage alternating current side, thus for the time being rendering the remaining transmitters inoperative, since removal of the alternating current supply source resulted in the loss of high potential direct current to the transmitters.

It has previously been impractical to switch the transmitters individually on their high voltage direct current side, by reason of the destructive arcing which was apt to develop across the opening contacts.

It is an object of my invention to provide means whereby a high voltage direct-current circuit may be opened without arcing across the opening contacts.

It is a further object of my invention to provide means whereby a plurality of apparatus fed from a common type voltage direct current source may be individually cut in or out of the supply circuit.

An additional object of my invention resides in a method for eliminating arcing upon the opening of a high voltage direct-current circuit.

Additional objects of my invention will be brought out in the following description of the same, taken in conjunction with the accompany- 50 ing drawing whereint- Figures 1, 3, and 5 are circuits illustrating various embodiments of my invention whereas Figures 2, 4, and 6 are curves depicting the transient conditions existing respectively in the 55 circuits of Figures 1, 3, and 5.

Fig. 7 is a. circuit embodying my invention as applied to a keying circuit of a radio transmitter.

Fig. 8 is a circuit diagram illustrating the application of my invention to a system, wherein a plurality of loads are supplied from a common po- 5 tential supply source.

A more specific description of these circuits and operating characteristics follows.

In Fig. 1 I have shown a source of high voltage direct current potential I followed by a filter 10 comprising a series choke 3, a pair of condensers 5 and I connected in parallel, the filter feeding a load 9 which may represent practically any type of load but in this case might indicate a transmitter. The direct current source of high volt- 15 age shown in the form of a direct-current generator is merely representative of any source of high voltage direct-current and, therefore, may

the equivalent of one condenser and would nor- -mally comprise a single condenser in the cus- 25 tomary filter circuit. I have found, however, that by splitting this condenser up into two parallel connected condensers of equivalent value, as shown, it would be possible to open the circuit at a point in the main line between the two condensers, without obtaining arcing across the contacts I I, upon opening of the circuit.

The theory involved in preventing the occurrence of arcing may be understood by a brief reference to the curves of Fig. 2 wherein the horizontal line H! represents the value of the applied direct current potential from the generator I, the superimposed oscillating transient curve l5 representing the alternating current component of 40 potential superimposed upon the direct current value due to the oscillations initiated by the discharge of the first filter condenser 5 through the inductance 3 in series therewith plus whatever inductance may be present in the generator. In 45 some cases the inductance of the generator windings alone constitutes the sole inductance of the circuit, in which cases, the inductance 3 would be omitted as a separate element. v

In series with the direct current potential but of opposite polarity thereto, considering the right hand contact as a reference point, we have at the instant of breaking of the circuit, a voltage source A transient condition is set up by the potential bound up in this condenser resulting in a gradual discharge and consequently a gradual decrease in' the series opposing voltage. As

represented by the condenser discharge curve I! of Fig. 2, the voltage across the condenser approaches the value of zero at which moment the voltage across the open contacts H will apthe presence of a series bucking voltage of approximately the value of the direct current applied voltage, there will be no voltage drop impressed across the contacts at the instant of opening. This is an ideal condition for opening a high voltage circuit. The voltage across these contacts, however, begins to build up to a value approaching that of the high direct current voltage, but it should be borne in mind that during the time, during which this voltage is building up, the contacts are moving apart very rapidly and the voltage necessary to produce breakdown, therefore, increases greatly in value over what it was at the start. By proper design of the circuit constants, it will be possible to so prolong the building up of. the voltage across the contacts H during opening that the voltage at any instant will never reach the breakdown value for any instantaneous position of the contacts. This can readily be determined by oscillograph methods or by calculation and the plotting of curves such as shown in Fig. 2.

The condenser 5 performs an important function in this circuit in that it serves to prevent high inductive voltages from being developed across whatever inductance may be in the circuit, such as the inductor 3 or the inductance of the direct current source I.

Curve I9 of Fig. 2 which may be obtained by adding curves i5 and i1, represents the changes in voltage across the contacts during and after opening, whereas curve 2| indicates breakdown voltages throughout this same period for a given speed of opening of the contacts. It is apparent from these curves that arcing across the contacts cannot occur as long as the curve l9 lies wholly below the curve 2|.

Should it be desired that the circuit be opened only on overloads, the inductance and capacities of the circuit may be designed to take care of the situation and prevent arcing in the same manexisting circuit elements and opening the contacts between the filter condensers thoroughly isolates the load circuit represented by the resistor 9, but which resistor may constitute one of many transmitters fed from the same power source.

In some cases, there may be no filter present such as disclosed in Fig. 1. It has been the practice in such cases to merely shunt the opening contacts of the circuit with a condenser, the function of which was to absorb a large amount of the energy whichwould normally go into building up a high voltage across the opening contacts, causing breakdown or arcing.

In Fig, 3, I have shown such a circuit modified to the extent of improving the same materially.

This circuit comprises a source of. high voltage direct current which may constitute a. high voltage direct current generator I or a source of low voltage alternating-current stepped up and rectified to give high voltage direct-current. The output of this high voltage direct current source is fed to a load represented by the resistor 9 through a series inductance 3. serially included in this load circuit are two pairs of series connected contacts, one pair oi which, 23, is shunted by a resistor 25 in parallel with a series connected resistor 21 and condenser 29. v

Upon opening the shunted contacts 23, the entire circuit is forced into oscillation due to the presence of the inductance 3 in series with the condenser 29, thus causing the current in the circuit to pass through a zero value during oscillations as depicted by curve 34 of Fig. 4. Upon opening the second pair of contacts 3|,the formation of an arc thereacross is'avoided by reason of the fact that an oscillatory current has now supplanted the direct current which formerly existed, and this oscillatory current passes through zero value twice every cycle; and at the same time, its peak values are decreasing and approaching zero; as this oscillatory condition which has been set up as a result of. opening contacts 23 is of a transient character. Thus at any moment that the contacts 3| may be opened during this transient condition, the current across these contacts is bound to pass through a zero value and thus overcome any tendency for an arc to form. The decreasing amplitude of the current is also an aid toward this end.

Should there be no inductance in the circuit, there will be no oscillatory transients occurring therein and in lieu thereof, there will be a gradual decay of current from a maximum value to a zero value as illustrated by curve 36 of Fig. 4, the current at.no time changing its direction of flow and consequently never passing through the zero value. The presence of the'inductance, therefore, is essential to obtain zero values of current at the instant of opening the second pair of contacts.

The resistance 25 connected in shunt to the condenser 29 serves to relieve the condenser of any charge which will build up therein upon opening of the contacts II and the low resistance 21 in serieswith the condenser 29 merely serves to prevent too heavy a charging current thereto, upon closing of the contacts 3| in the circuit, the contacts being preferably closed in the reverse order of their opening.

The circuit of Fig. 3 just described, is satisfactory where the load is more or less constant in nature and the time of opening of the second pair of contacts may be predetermined, so that opening will occur when the transient oscillatory current in the circuit reaches approximately a zero value.-

Where the load is apt to be of a varying character, itmight be preferable to so control the opening of the second pair of contacts that they can open only when the current in the circuit reaches a predetermined low value. This can be very conveniently accomplished by placing in series with the contacts a relay coil 33 so designed that it will not open its associated contacts until the current has reached the desired low value, this relay coil-controlling the operation of the the load side of the contacts ll.

second pair of contacts 3L. In the circuit of Fig. 3, I have shown this alternative arrangement by means of a switch 35 adapted to alternatively connect to the second pair of contacts directly or through the relay control coil 33.

' an inductance 31 in series therewith and in shunt to this inductive load, I place a condenser I on The voltage across the contacts at'any instant will be the difference between the generator direct current voltage and the voltage across the condenser I or inductive load circuit. Upon opening of the contacts, the load circuit will be set into oscillation, transient in character, due to the presence of the shunting condenser I, and the voltage across the opening contacts will vary in accordance with the oscillatory curve 39 of Fig. 6 which represents the instantaneous diiference between the applied direct current voltage from the source I, represented by the horizontal line 4| and the oscillatory voltage generated or developed across the condenser 1 as illustrated by curve 43. It will be noted that the curve 39 which represents the voltage across the contacts at the instant of opening the circuits is zero in value which is the ideal value to prevent the formation of any arcs or discharges.

For the set of conditions illustrated by the curves of Fig. 6, the contacts must be completely opened within approximately a quarter of a cycle, in order to keep the voltage across the opening contacts from ever extending into the region above the breakdown value curve 2|. It will be apparent from a study of these curves that slower opening of the contacts may be obtained by either highly damping the oscillator circuit .or reducing the frequency thereof.

The constants of the circuit and the speed of operation or opening of the contacts will, therefre,'necessarily depend upon the predetermined value of the applied direct current potential and the constants of the load, but once these factorsare known, the rest may readily be determined.

The circuit of Fig. 7 illustrates the manner in which my invention may be applied to prevent key clicks in a keying circuit of a transmitter, key clicks being usually the result of transients caused by arcing at the key contacts. The circuit comprises an electron discharge device 45 having a grid 41, filament 49 and a plate electrode plate potential being supplied from a source of direct current voltage which may either constitute a battery, direct-current generator, or an alternating-current supply in combination with a rectifier and filter. Across the power supply source is a potentiometer or voltage divider comprising the

resistors

53 and 55 with the filament of the discharge device connected to a point therebetween. That portion of the potentiometer 55 toward the positive terminal of the supply source constitutes the portion from which the anode potentials may be derived, whereas that portion of the resistor 53 toward the negative end of the supply source provides bias potential for the tube. Condensers 51 and 59 are providedin shunt with these portions of the voltage divider, and a filter condenser 5| is connected across the terminals of the supply source. The

input circuit includes, in addition to the biasing resistor, an inductor O3 in series therewith, and this input circuit may be capacitively coupled by means of a condenser 65 to a source of carrier frequency 61 which may either be a preceding amplifier or an oscillator. The output from this keying circuit may be derived by transformer coupling 69 from a tank circuit II in the plate circuit of the tube.

Keying of the carrier frequency energy may be I advantages of arc-preventing feature described in connection with the circuits of Fig. l in combination with the condenser resistor shunted contacts of Fig. 3. That portion of thecircuit involving the plate circuit of the tube bears similarity to Fig. l in that the tank circuit and plate to cathode impedance constitutes the equivalent of the load of Fig. 1, which in turn, is shunted by a condenser 59, which is the equivalent of the condenser I. The inductance 3 of the circuit of Fig. l finds its counterpart in the inductance of the supply source which may either be the inductance in the windings oi the generator, if a generator be used, or it may be the inductance in the filter should the energy be derived from a rectified and filtered alternating-current supply.

Thekeyshuntedby the resistor 53 and a parallel connected condenser 51 is similar to that portion of the circuit of Fig. 3, which discloses the contacts 23 as being shunted by a resistor 25 and a parallel connected condenser 29.

The combined action of these two means for avoiding the formation of arcs across the key contacts will result in a keying circuit free of the undesirable key clicks which normally occur in circuits, in which no provision is made to prevent or avoid the formation of arcs across the key contacts during keying.

In the circuits of Figs. 1, 3 and 5, the invention was described in connection with the opening of a high voltage direct current circuit to a single load. To fulfill the additional objects of my invention, wherein a plurality of loads may be connected to a common source of high voltage direct current, I have illustrated in Fig. 8 a source of high voltage direct current feeding l a plurality of independent loads 9 which may represent different transmitters or other loads for that matter. The direct current source may comprise any of the forms described above in connection with Figs. 1, 3 and 5, feeding energy through a filter comprising the series inductance 3 and shunt condenser 5, which correspond to the similar elements of the circuit of Fig. l. Across each load is placed a shunting condenser l which corresponds to the shunting condenser of the load in the circuit of Fig. 1. Between each of these shunting condensers and the common filter condenser 5 is placed a switch 15 corresponding to the opening contacts ll of the circuit of Fig. 1. Charging current limiting resistors 22, similar to that discussed in connection with the circuit of Fig. 1 may also be embodied in this circuit and would be connected one in series with each of these shunting condensers 'l.

The circuit of Fig. 8 is similar in all respects to that of Flg. 1, except inlthat a number of loads with their corresponding shunting condensers and opening contacts are connected in parallel. From a description of the theory of operation of the circuit of Fig. 1, it becomes apparent now that any one or more of the individual loads which may represent diflerent trans-= mitters may be disconnected from the power supply without in any way interfering with the operation of the remaining loads connected in the circuit. It no longer is necessary to open the power supply circuit itself, thereby rendering all of the loads inoperative during the time when one or more are being removed from the circuit.

From the above discussion it becomes apparent that these circuits and modifications described above fulfill the objects of my invention. Various modifications may be apparent to those skilled in the art, and it is my desire that my invention be not limited to the specific details described and disclosed but that it shall be limited only by the prior art and the appended claims.

I claim as my invention:

1. In combination, a source of direct-current power, a load circuit connected thereto, means for opening the circuit so as to effectively disconnect the load from the power source, a condenser connected to the load for maintaining a voltage across the load during the interim of opening said circuit, a condenser connected across the source of direct-current power, and a.

resistor in series with said first condenser;

2. In combination, a source of direct-current power, a load circuit therefor, a switch for opening the'circuit so as to effectively disconnect the load circuit from the power source, a condenser connected to the load circuit to maintain voltage across the load circuit during the interim of switch opening, a condenser connected across said direct-current power source, the difference between said load voltage and the voltage of said second condenser during opening of said circuit being always less than a value which would power, a load circuit therefon'a switch for opening the circuit so as to effectively disconnect the load circuit from the power source, means connected to the load circuit to maintain voltage 4 across the load circuit during the interim of switch opening, and means connected to the power source to prevent high inductive voltages during the interim of switch opening, the difference between said load voltage and, the voltage of said source during opening of said circuit being always less than a value which would cause arcing across the contacts of said switch, and means for limiting the charging current to said load voltage maintaining means upon the closing of said switch.

' REUBEN LEE.