US3330992A

US3330992A - Electric switch

Info

Publication number: US3330992A
Application number: US411302A
Authority: US
Inventors: Allen R Perrins
Original assignee: Superior Electric Co
Current assignee: Superior Electric Co
Priority date: 1964-11-16
Filing date: 1964-11-16
Publication date: 1967-07-11
Anticipated expiration: 1984-07-11

Description

United States Patent 3,330,992 ELECTRIC SWITCH Allen R. Perrins, Cheshire, Conn., assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed Nov. 16, 1964, Ser. No. 411,302 7 Claims. (Cl. 317-11) The present invention relates to an electric switch having movable contacts for opening and closing a circuit and more particularly to such a switch which is capable of controlling large electrical quantities Without malfunctioning even over an extended period of use with many operations.

Electrical switches of the type having at least one pair of contacts that are positionable against each other at closure of a circuit and away from each other during opening of a circuit have presented substantially no difiiculties in either of these two positions. However, and especially when employed in circuits where there are relatively large electrical quantities being-controlled by the switch, difiiculties have arisen when the contacts are changing from one of these positions to the other. These difiiculties primarily result in a destruction and/or malfunctioning of the contacts and are generally traceable to a continuation or initiation of current flow between the two contacts when the two contacts are separated by an air gap which the current can bridge. Such current flow has sometimes been referred to as arcing and it causes pitting, oxidizing and other detrimental changes in the physical condition of the contacts which not only severaly limit their usable life but even when closed, effect poor electrical conduction therebetween with accompanying heat which may even prevent the subsequent opening of the contacts. To support arcing, at least a voltage, either source or resulting from a change of condition, must exist between the two spaced-apart contacts which is sufiicient to force current between this air gap.

It is accordingly an object of the present invention to provide an electric switch which substantially eliminates arcing at its pair of contacts when moving from one position to the other even when controlling relatively large quantities of electrical power.

Another object of the present invention is to provide an electric switch having a pair of contacts in which during the time that the contacts are changing their position, only a small, minute voltage is caused to exist therebetween which is insuflicient to detrimentally effect the contacts by supporting substantial arcing between the contacts.

A further object of the present invention is to provide an electric switch which eliminates arcing during the changing of the positions of its contacts but which also does not add any additional resistance or impedance in the circuit during its closed position than a conventional, substantially impedance free, switch.

A still further object of the present invention is to achieve the above objects with an electric switch that for the purposes intended is relatively economical to manufacture, composed of relatively few parts, is extremely durable in use over a wide range of electrical conditions and operates positively to open or close a circuit.

In carrying out the present invention there is provided an electric switch that includes at least a pair of contacts that are capable of being maintained in an open position or a closed position and an actuator for moving the contacts from one position to the other. The contacts are connected to form a path that is in series with a load or power consuming device and a source of electrical energy to control the electric current to the load and thus the load current passes through the contacts. Connected in parallel to the load carrying contacts for also carrying the load current at selected times is another path that includes at least one semiconductor element of the type that requires a signal to render it conducting but will continue conducting until the current therethrough and hence the voltage thereacross is reduced to a small value at which time it will cease conducting. Thus under normal usage, the load current flow through the semiconductor can be initiated when both a value of voltage sufiicient to maintain conduction exists across the semiconductor and also a signal is applied. For other conditions, within its functioning range, it will not conduct. One such semiconductor device is a controlled rectifier and the switch of the present invention utilizes these characteristics of the controlled rectifier to achieve the above objects.

In the operation of the electric switch from its open to its closed position, current to the load is initially conducted through the semiconductor path for perhaps a few cycles of alternating current and then the main contact path is closed by the main contacts coming together. At the time of closing, the voltage between the two main contacts is only the voltage drop across the semiconductor path and may be only on the order of a few volts, thus preventing arcing between the contacts by having only a small voltage existing between the contacts when they are separated by a small air gap. When the contacts are in engagement and load current is being conducted through them, the voltage drop in the main contact path is very low, and may be less than one half a volt, which is insufiicient to maintain conduction through the controlled rectifiers even with a signal applied thereto. Thus the load current only passes through the main contact path as the semiconductor path is elfectively removed from the circuit.

Upon opening of the switch, the main contacts are initially opened and as soon as the main contacts are separated sufficiently to produce a voltage thereacross which is greater than that needed to maintain conduction through the semiconductor path, a signal is applied to the semiconductor. The signal renders the semiconductor conducting providing a relatively low resistance path and load current will then flow through the semiconductor path. With the semiconductor path conducting the load current, there is only a small voltage drop in this path and thus the voltage across the main contacts is limited to this small value of voltage which is insuflicient to maintain arcing of load current across even a small air gap eXiSting between the main contacts. After a few cycles of alternating current, a signal is prevented from being applied to the semiconductor thereby causing it to cease conduction at the termination of the final half cycle of alternating current of load current.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is an electrical schematic diagram of the electric switch of the present invention.

FIG. 2 is a detail partly in section showing the mechanical construction of portions of the switch.

FIG. 3 is a view taken on the line 33 of FIG. 2.

Referring to the drawing, the electric switch of the present invention is generally indicated by the reference numeral and has a pair of

terminals

11 and 12. The terminal 12 is connected to a load circuit, generally indicated by the reference numeral 13 having its other end connected to a terminal 14 with the

terminals

11 and 14 being connected to a source of alternating current (not shown). it will thus be appreciated that the switch 10 controls the current from the source to the load circuit.

In carrying out the present invention there is provided a main contact path, generally indicated by the reference numeral 15, which includes a main switch 16 having

separable contacts

17 and 17 connected between the terminal 11 and the terminal 12. In addition, there is provided a semiconductor path 18 paralleling the path between the

terminals

11 and 12. The semiconductor path while it may utilize a three electrode A.C. semiconductor switch that is triggered into conduction in either direction by a gate signal, in the embodiment shown herein it includes a pair of controlled

rectifiers

19 and 20 that are parallelly and inversely connected to permit both half cycles of alternating current to flow through the path 18.

For etfecting a gate signal to the controlled rectifier 19 to render it conducting if sufficient voltage exists thereacross, there is provided a resistance 21 while a resistance 22 similarly functions for the controlled rectifier 20.

Diodes

23 and 24 are utilized to prevent transverse cathode gate voltage while another resistance 25 is employed to provide with resistances 21 and 22 a voltage divider to the gate power. A condenser 25a parallels the resistance 25 and accelerates the application of the gate signal. A gate switch 26 is connected between the

resistances

22 and 25 as shown.

Connected in series with the

semiconductors

19 and 20 in the path 18 is an impedance 27 of low value that may take the form of a coiled resistance wire, to limit surge current through the semiconductor path to within the ratings of the controlled rectifiers and current rate of rise. The semiconductor path also includes a semiconductor path switch 28.

In the operation of the switch, assuming that the electric switch 10 has all

switches

16, 26 and 28 in the solid line position shown where they are all open, and the terminal 11 is positive, there is no load current to the load circuit 13. The switch 28 is initially closed enabling current to be conducted from the terminal 11 through the switch 28, resistance 27, diode 24 and until switch 26 is closed no current flows through the semiconductor path as the semiconductors are not conducting and hence there is no voltage existing across the switch 28. After closure of the switch 28, a voltage exists between the anode and cathode of the controlled rectifier 19 and with closure of the switch 26 a gate signal is applied to the controlled rectifier 19 causing rectifier 19 to conduct to pass load current from the terminal 11 to the terminal 12. Shortly after closure of the switch 26 preferably witln'n one or two half cycles of alternating current, the main contact switch 16 is closed providing in eifect a short-circuit path around the semiconductor path 18. A

At the time of the closing of the main contacts one of the controlled rectifiers is conducting, and thus the voltage across the

contacts

17 and 17 is only the voltage drop through the semiconductor path which effectively is only a few volts. These few volts are insufficient to cause arcing between the contacts as they approach each other to close. Upon the closing of the

contacts

17 and 17, the voltage across the path 18 is so small that even with the switch 26 closed there is insufiicient voltage across the semiconductor path to provide the voltage across the controlled rectifier sufficient to maintain it conducting, even with a gate signal. Accordingly it ceases conduction with the load current thus being carried completely through the main switch 16 and path 15 to the load circuit 13.

It will be appreciated that in the semiconductor path for the half cycles of alternating current when the terminal 14 is positive the controlled rectifier 20 conducts, if conditions for its conduction exist. With load current flowing in the path 15 to the load circuit 13 and it being desirous to interrupt the current by opening the switch 10, initially the switch 16 is opened by separation of the

contacts

17 and 17. This will cause almost instantaneous conduction of either controlled

rectifier

19 or 20 and thus at the time of opening of the switch 16, the voltage across the switch contacts is not permitted to increase beyond a small value, i.e. being at the most the voltage drop across the semiconductor path 18. After a cycle or less the switch 26 is opened and it will be appreciated that at the time of opening the switch 26, only a small voltage and current, i.e. gate current, is present at that switch, thus preventing arcing at the switch 26. The opening of switch 26 ceases the application of a gate signal to the semiconductors and they will cease conduction at the next zero crossing of the alternating current. The switch 28 is opened at least one cycle after opening of the switch 26 to insure that neither semiconductor is conducting. The switch 28 is opened with substantially no voltage thereacross at the time of its opening as the semiconductors are not conducting. Switch 28 after opening prevents leakage current from flowing through the semiconductor path.

It will be appreciated that in the open position switch 28 merely serves to prevent voltage from being applied to the controlled

rectifiers

19 and 20. Also it will be understood that the firing circuits for the controlled

rectifiers

19 and 20 are of the type that are generally referred to as A.C. firing circuits and that conduction of the controlled rectifiers occurs shortly after the beginning of the half cycle :or may occur any time thereafter so long as the voltage across the controlled rectifier and the gate current is sufiicient to render and maintain the controlled rectifier conducting. With the

switches

28 and 26 closed and also the main switch16 closed the conditions for applying a gate signal to the controlled rectifiers continuously exists but as explained the controlled rectifiers do not conduct. However, with this construction, the gate firing circuit is always immediately responsive to produce a gate signal as soon as the voltage across the semiconductor path is sufiicient. It will furthermore be appreciated that the controlled

rectifiers

19 and 20 are only conductive for one or two half cycles each time the switch is operated, and thus steady state heat dissipation requirements are obviated.

The

switches

16, 26 and 28 may be operated in the above sequence by any desired manner of mechanical actuation. Shown in FIGS. 2 and 3 is one possible embodiment in which a single actuator is employed to operate the switches in the above-recited sequence. The main switch 16 is shown in its closed position with the contact 17 being connected to the terminal 11 while the contact 17 is connected to the terminal 12. Bridging the two contacts is an arm 17a having opposite end portions that engage the contacts 17 and 17' and if arcing should occur, would occur between the bridging arm 17a and the contacts 17 and 17'. The arm 17a is mounted on a sliding member 29 mounted for reciprocating movement between the solid line position wherein the switch 10 is closed and the dotted line position where the switch 10 is opened.

The sliding member 29 is connected to an actuator 30 which in the disclosed embodiment is a rectangular knob 31 that is manually manipulatable between its solid line switch on position and its dotted line switch off position. It will be understood that the actuator 30 may take other forms and be other than manually manipulatable it desired. For maintaining the actuator 30 in either of its positions and for quickly changing from one position to the other there is provided an overcenter linkage consisting of an arm 32 pivoted as at 33 to a frame 34 and a second arm 35 pivoted as at 36 to the arm 32. The sliding member 29 carries a pin 37 that is pivotally secured to the other end of the arm 35. A guide 39 having a U-shaped slot is secured on the frame 34 for assuring linear movement of the pin 37 and hence the sliding member 29 by the pin being movable in the slot. The actuator 30 further includes a lug 40 to which one end of a spring 41 is secured, the other end of the spring engaging a pin 42 carried by the arm 32. Thus, in the solid line position of the parts as shown, the lug 40 is located leftwardly of the pin 33 thus maintaining the

arms

32 and 35 in the position shown wherein the switch 16 is closed. With the actuator in its dotted line position the lug 40 is on the other or right-hand side of the pin 33 causing the linkage to assume a bent condition thereby shortening it and placing the contacts in their dotted line open position.

It will be appreciated that the sliding member 29 is thus moved with a snap action from one of its positions to the other with the position depending upon the relative location between the lug 40 and the pivot 33 and that the movement from one position to another is in effect a relatively fast snap action irrespective of the slowness of the movement of the actuator.

In order to provide the desired sequence of operation of the

switches

16, 26 and 28, the sliding member 29 carlies a camming surface 43 projecting outwardly therefrom and formed from insulating material.

Switches

26 and 28 are of the normally open type and have arms 26' and 28 that are positioned to engage the surface 43. The surface 43 includes a lower part 43' and an upper part 43" with the part 43' when engaging the arms 26' and 28' effecting closing of the

switches

26 and 28 respectively While the part 43 when engaged by the switch arms 26' and 28 enabling the switches to be open.

With the structure and with the switch in the solid line position, upon the actuator 30 being moved towards its dotted line position to open the electric switch 10, after the lug 40 passes beyond the pivot 33, the sliding member 29 is snapped to its open position by the

arms

32 and 35 assuming an angular relationship. The action is quite rapid being on the order of two hundredths of a second or about one and one-half cycles of 60 cycle alternating current. However with this movement initially the switch 16 is opened while the

switches

26 and 28 are maintained closed. After a little more rightward movement of the sliding member 29 to increase the opening of the contacts, the switch arm 26 engages the camming surface 43" causing the switch 26 to open and further movement of the sliding member 29 towards its dotted line open position enables the switch arm 28 to engage the camming surface 43" thereby opening this switch.

With the actuator being moved from its open to its closed position, the sliding member 29 moving leftwardly in FIGS. 2 and 3, the switch arm 28' will initially engage the camming surface 43' to be closed, then the surface 43 closes the switch 26 and then the switch 16 is closed. The camming surface 43' maintains the two

switches

26 and 28 closed while the main switch 16 is closed. As soon as the main switch 16 is closed, the semiconductors cease conducting. However, the

switches

26 and 28 are in position to provide a gate signal when the main switch 16 has started to open.

It will accordingly be appreciated that there has been disclosed an electric switch for controlling relatively large values of electrical energy which acts in its open and closed positions as a conventional switch. The switch of the present invention, however, substantially minimizes if not eliminates difiiculties occurring in conventional switches by limiting the value of voltage that may exist between the main contacts of the switch when changing from one position to the other to only a small voltage,

irrespective of the voltage controlled by the switch. The small voltage is insuflicient to support current flow or arcing between the contacts when they are separated by a small air gap and thus the switch of the present invention obviates the detrimental effects which occur in conventional switches and seriously limit their usable life.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An electric switch for controlling the flow of load current to an electric load comprising a first terminal connectible to a source of electrical energy, a second terminal connectible to an electric load, a pair of contacts connected in series between said first and second terminals and forming a first load current path, said contacts being mounted for movement between an open and a closed position, a second load current path connected in parallel to said first path between the first and second terminals, said second load current path including semiconductor means having load current elements and a triggering element with a signal on said triggering element of at least a minimum voltage causing the semiconductor to conduct, actuatable means connected to the pair of contacts for moving said pair of contacts from their open position to their closed position, and means upon operation of the actuatable means for applying a triggering signal to said triggering element prior to the contacts engaging each other for rendering said second load current path conductive of load current, said lastnamed means being interconnected with the terminals and supplying a triggering signal only when the voltage between the terminals has at least a minimum value.

2. The invention as defined in claim 1 in which said last-named means is operable to continually apply a tn'ggering signal to said triggering element when the contacts are closed but only if the voltage between the terminals is above the minimum value and in which the first load current path has a resistance which is sufiiciently low to develop a voltage between the terminals which is less than the minimum voltage required to enable conduction between the load elements of the semiconductor means.

3. The invention as defined in claim 1 in which said last-named means is connected to said actuating means and is rendered operable at a preselected distance of said cont-acts from each other.

4. The invention as defined in claim 3 in which the second load current path includes a switch, means interconnecting said switch to said actuating means to close said switch prior to applying a triggering signal to said triggering element and for opening said switch when said contacts are opened after cessation of conduction of the semiconductor means.

5. An electric switch for controlling load current to an electric load comprising a first terminal connectible to a source of alternating current, a second terminal connectible to an electric load, a pair of contacts connected in series between said first and second terminals, actuator means for opening and closing said contacts with the contacts being closed forming a first load current path, a second load current path connected between said first and second terminals in parallel to said first load current path, semiconductor means having load current carrying elements connected in series in said second load current path and having a triggering element, signal means for applying a signal to said triggering element with said signal having at least a minimum voltage value, means interconnecting the signal means to the terminals to cause a triggering signal only when a value of voltage exists across the terminals that is greater than the minimum value and means interconnected to the signal means for ceasing operation of the signal means after the contacts have become separated a distance through which the source voltage cannot cause load current to be conducted.

6. The invention as defined in claim 5 in which the signal means includes a triggering switch having a closed position when a triggering signal is applied and an open position which prevents the application of said triggering signal, and means connected to said actuator means for closing said triggering switch when the contacts are separated by a small air gap and opening said triggering switch when the contacts are at their open position.

7. The invention as defined in claim 6 in which there is a switch connected in series in the second load current path and means connecting said'switch with said actuatable means to cause said switch to be closed prior to 8. closing of saidtriggering'switch and opened subsequent to the opening of said triggering switch.

References Cited UNITED STATES PATENTS 2,441,789 5/1948 Bivens 317-11 x 2,789,253 4/1957 Vang 317-11 3,237,030 2/1966 Coburn 317-11 X 1 MILTON O. HIRSHFIELD, Primary Examiner.

J. D. TRAMMELL, Assistant Examiner.

Claims

1. AN ELECTRIC SWITCH FOR CONTROLLING THE FLOW OF LOAD CURRENT TO AN ELECTRIC LOAD COMPRISING A FIRST TERMINAL CONNECTIBLE TO A SOURCE OF ELECTRICAL ENERGY, A SECOND TERMINAL CONNECTIBLE TO AN ELECTRIC LOAD, A PAIR OF CONTACTS CONNECTED IN SERIES BETWEEN SAID FIRST AND SECOND TERMINALS AND FORMING A FIRST LOAD CURRENT PATH, SAID CONTACTS BEING MOUNTED FOR MOVEMENT BETWEEN AN OPEN AND A CLOSED POSITION, A SECOND LOAD CURRENT PATH CONNECTED IN PARALLEL TO SAID FIRST PATH BETWEEN THE FIRST AND SECOND TERMINALS, SAID SECOND LOAD CURRENT PATH INCLUDING SEMICONDUCTOR MEANS HAVING LOAD CURRENT ELEMENTS AND A TRIGGERING ELEMENT WITH A SIGNAL ON SAID TRIGGERING ELEMENT OF AT LEAST A MINIMUM VOLTAGE CAUSING THE SEMICONDUCTOR TO CONDUCT, ACTUATABLE MEANS CONNECTED TO THE PAIR OF CONTACTS FOR MOVING SAID PAIR OF CONTACTS FROM THEIR OPEN POSITION TO THEIR CLOSED POSITION, AND MEANS UPON OPERATION OF THE ACTUABLE MEANS FOR APPLYING A TRIGGERING SIGNAL TO SAID TRIGGERING ELEMENT PRIOR TO THE CONTACTS ENGAGING EACH OTHER FOR RENDERING SAID SECOND LOAD CURRENT PATH CONDUCTIVE OF LOAD CURRENT, SAID LASTNAMED MEANS BEING INTERCONNECTED WITH THE TERMINALS AND SUPPLYING A TRIGGERING SIGNAL ONLY WHEN THE VOLTAGE BETWEEN THE TERMINALS HAS AT LEAST A MINIMUM VALUE.