Two Terminal Arc Suppressor

Abstract

A two terminal arc suppressor for protecting switch, relay or contactor contacts and the like comprises a two terminal module adapted to be attached in parallel with the contacts to be protected and including a circuit for deriving an operating voltage upon the transitioning of the switch, relay or contactor contacts from a closed to an open disposition, the power being rectified arid the resulting DC signal used to trigger a power triac switch via an optoisolator circuit whereby arc suppression pulses are generated for short predetermined intervals only at a transition of the mechanical switch, relay or contactor contacts from an closed to an open transition and, again, at an open to a close transition during contact bounce conditions.

Claims

1. An arc suppressor for switchable contacts coupling a voltage source to a load, said arc suppressor comprising: (a) a pair of terminals adapted to be connected across a set of switchable contacts to be protected; (b) a solid state triggerable switch connected between the pair of terminals; (c) a triggering circuit operatively coupled to the solid state triggerable switch operative upon the switchable contacts moving from a closed state to an open state for driving the solid state triggerable switch into a conductive state to short out the switchable contacts; and (d) a pinch-off circuit coupled to the triggering circuit for controlling the length of time that the solid state triggerable switch remains in said conductive state following movement of the switchable contacts from the closed state to the open state.

Description

DESCRIPTION OF THE DRAWINGS

[0033] The forgoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description, especially when considered in conjunction with the accompanying drawings in which like the numerals in the several views refer to the corresponding parts:

[0034] FIG. 1 is a block diagram illustrating the manner in which an arc suppressor in accordance with this invention is connected in circuit with contacts to be protected.

[0035] FIG. 2 illustrates generally an example of a two terminal arc suppressor block diagram;

[0036] FIG. 3 illustrates generally an example of an AC two terminal arc suppressor schematic diagram;

[0037] FIG. 4 illustrates generally an example of a DC two terminal arc suppressor schematic diagram.

[0038] FIG. 5 illustrates generally an example of a two terminal arc suppressor timing diagram; and

[0039] FIG. 6 illustrates generally an example of a circuit package, a two terminal arc suppressor of the present invention.

DETAILED DESCRIPTION

[0040] The following detailed description relates to a two terminal arc suppressor directed toward extending the life of switches, relays and contactors used to switch either an alternating current (AC) or a direct current (DC) source to a load.

[0041] The following detailed description includes discussion of a two terminal arc suppressor connected to a mechanical switch, relay or contactor. Additionally, elements of a two terminal arc suppressor discussed including a contact power harvester, a pinch-off circuit, a triggering circuit, a solid state triggerable switch, an RC snubber circuit, contact lead terminals, a voltage surge limiter and a timing diagram is included.

[0042] The present invention can be readily understood from a discussion of FIGS. 1 through 6.

[0043] FIG. 1 illustrates generally an example of a system including a two terminal arc suppressor 8. In an example, an AC or a DC power source 1 is connected via wire 2 to the terminal 3 of a mechanical switch, relay or contactor contact for further connection to the mechanical switch, relay or contactor wiring 6 to the mechanical switch, relay or contactor 9. A load 16 is connected, via wire 15, to the second terminal 12 of the mechanical switch, relay or contactor for further connection, via the internal mechanical switch, relay or contactor wiring 10, to the mechanical switch, relay or contactor 9. A first wiring terminal 5 of the two terminal arc suppressor 8 comprising the present invention is connected to the mechanical switch, relay or contactor terminal 3 via its internal wiring 7, and its wire terminal 5 and through an external wire 4. The second wiring terminal 14 of the two terminal arc suppressor 8 is connected to the mechanical switch, relay or contactor terminal 12 via its internal wiring 11, its wire terminal 14 and through an external wire 13. Thus, the arc suppressor 8 is connected directly in parallel with the contacts to be protected.

[0044] FIG. 2 illustrates generally by means of a block diagram an example of a functional circuit of the two terminal arc suppressor 8. In this embodiment, the internal wiring bus 7 of the two terminal arc suppressor 8 is common and shared with a contact power harvester 24, a triggering circuit 32, a solid state triggerable switch 36, an RC snubber circuit 38, contact lead terminals 40 and a voltage surge limiter 42. The internal wiring bus 11 of the two terminal arc suppressor 8 is common and shared with the contact power harvester 24, the solid state triggerable switch 36, an RC snubber circuit 38, contact lead terminals 40 and a voltage surge limiter 42. The triggering circuit 32 connects to common resistor capacitor node of the RC snubber circuit 38 via a connection 44. The contact power harvester 24 connects via connection 26 to the pinch-off circuit 28. The pinch-off circuit 28 then connects, via connection 30, to the triggering circuit 32. The triggering circuit 32 connects, via connection 34, to the solid state triggerable switch 36,

[0045] FIG. 3 illustrates by a circuit schematic diagram an implement of an AC two terminal arc suppressor comprising an exemplary embodiment.

[0046] In FIG. 3, the voltage surge limiter 42 comprises a surge limiting element like a Metal Oxide Varistor (MOV) or Transient Voltage Suppressor (TVS) that is connected directly across the arc suppressor's input terminals 5 and 14 and in parallel with a triac Q2 which, along with resistors R5 and R6 that are connected in series between the internal bus wire 7 and a main terminal of the output of the IR detector section of an optoisolator triac U1 make up the solid state triggerable switch 36 shown in the block diagram of FIG. 2. A capacitor C5 and a resistor R4 constitute the RC snubber circuit 38 of FIG. 2 and the second main terminal of the output section of the optoisolator triac U1 is connected to the common terminal 44 between the capacitor C5 and the resistor R4.

[0047] The IR emitter diode 46 of the optoisolator triac U1 is connected across the DC output terminals of a full wave bridge rectifier BR2 and, marked +− in FIG. 3. The AC input terminals of the bridge rectifier are connected by a capacitor C4 and a conductor 45 between the internal buses 7 and 11. Thus, the triggering circuit 32 of FIG. 2 is made up of the IR emitter diode 46, the full wave bridge rectifier BR2, a capacitor C3 and an AC coupling capacitor C4.

[0048] The pinch-off circuit 28 of FIG. 2 comprises a NPN transistor Q1 whose collector and emitter terminals are connected across DC output terminals of the bridge rectifier BR2 and its base electrode is connected through a current limiting resistor R2 to a DC output terminal + of a further full wave bridge rectifier BR1. The transistor Q1 and the resistor R2 and capacitor C2 make up the pinch-off circuit 28 shown in the block diagram of FIG. 2.

[0049] The contact power harvester 24 of FIG. 2 is seen to comprise the AC coupling capacitor C1, the bridge rectifier BR1 and a conductor 47. So long as the contacts being protected are open, an AC voltage is applied to BR1 and a DC output is present to charge C2 to the point where Q1 becomes forward biased to turn off the optoisolator triac IR emitter diode 46 rendering Q2 non-conducting.

[0050] FIG. 4 illustrates a circuit schematic diagram of an implementation of a two terminal arc suppressor for a DC power source comprising an exemplary embodiment. In FIG. 4, the voltage surge limiter 42 comprises a surge limiting element such as a metal oxide Varistor or Transient Voltage Suppressor that is connected directly across the arc suppressor's input terminals 5′ and 14′ and in circuit with a NPN transistor Q10 which, along with resistors R11 and R12, are connected to the output of the IR detector section of an AC Darlington optoisolator driver U10 and make up the solid state triggerable switch 36 shown in FIG. 2. A capacitor C11 and a resistor R13 constitute the RC snubber circuit 38 of FIG. 2.

[0051] The oppositely poled IR emitter diodes of the AC Darlington optoisolator U10 are connected across the DC power contact via current limiting resistor R10 and differentiating and timing capacitor C10. As soon as the DC current carrying contact that is connected to terminals 5′ and 14′ transition from the closed to the open state, current rushes through C10 limited by R10 and forward biased either of the IR emitter diodes of U10. The IR detector section of U10 conducts a base current for Q10 so that Q10 becomes saturated and temporarily conducts the load current through bridge rectifier BR10. BR10 provides for non polarized operation of the DC two terminal arc suppressor.

[0052] In the timing diagram of FIG. 5 the arc suppression pulse duration is set by the product of R10 and C10 at a value in a range from about 0.1 ms to 10 ms. As soon as the DC current carrying contact that is connected to terminals 5′ and 14′ transition from the open to the closed state, C10 is discharged via R10 and again forward biases either of the IR emitter diodes of U10. The IR detector section of U10 conducts a base current for Q10 so that Q10 becomes saturated and temporarily conducts the load current through full-wave bridge rectifier BR10.

[0053] Having described the constructional features of the preferred embodiments of the two terminal arc suppressor for both AC and DC power sources, consideration will next be given to their mode of operation and, in this regard, reference will be made to the timing diagram of FIG. 5.

[0054] Timing graph 110 depicts the status of the contact state starting at a contact open state, followed by a contact transition to closed state, followed by a contact closed state and followed by a contact transition to open state. Timing graph 120 depicts the status of the contact are suppression pulse timing especially during the contact transition to closed state and the contact transition to open state. During the contact open state the contact power harvester 24 is able to harvest power from the AC terminals 3 and 12 of FIG. 1 because the switch, relay or contactor contacts are open and terminal 5 is not shorted to terminal 14. Thus, power is provided to the pinch-off circuit 28. This pinches off the power that activates the triggering circuit 32, thus preventing the triggering circuit 32 from triggering the solid state triggerable switch 36 from firing arc suppression pulses on wire terminals 5 and 14 via its internal connections 7 and 11.

[0055] During the contact closed state the contact power harvester 24 is shorted out and cannot harvest power as it could earlier from the open contact that is connected to terminals 5 and 14. As soon as the contact of the mechanical switch, relay or contactor 9 opens, an AC voltage is again present on the internal wiring connections 7 and 11 of the two terminal arc suppressor 8. As soon as voltage is available on the two internal wiring connections 7 and 11, the triggering circuit 32 receives AC current, via its AC coupling capacitor C4, wire connection 45, rectified by bridge rectifier BR2 and it is passed as a DC current through the IR emitter diode 46 of the input section of U1. As soon as current is flowing through the input section of U1, the output section of U1 in the triggering circuit 32 responds with placing the triac Q2 of the solid state triggerable switch 36 into the conduction state and, in effect, shorting out the connected contact of the mechanical switch, relay, or contactor 9 and taking over the current conduction for one half period of an AC power cycle.

[0056] At the same time, as the mechanical switch, relay or contactor 9 transitions to the open state, an AC voltage is available for the contact power harvester 24. As soon as AC voltage is available at the internal wire connections 7 and 11 of the two terminal arc suppressor, capacitor C1 and wire connection 47 of the contact power harvester circuit pass an AC current through bridge rectifier BR1. The rectified output of BR1 is available on its DC plus and minus terminals. A zener diode D1 limits the rectified DC voltage to a maximum voltage, in this example to 3.3V. As soon as DC voltage becomes available at the rectified output of BR1, capacitor C2 starts charging and making its charge voltage available to the base of Q1, via a current limiting resistor R2. The collector and emitter of Q1 connect to the input section of U1. U1 is already in the conducting state and, in return, firing power triac Q2 as soon as the contact made AC voltage available at terminals 5 and 14 through its action of transitioning from the closed to open state. A short time later, that is determined by the charging time constant of C2, the input voltage to U1 is pinched off by Q1 resulting in termination of the firing pulse, and resulting in holding of Q2 until the end of the current half cycle in that since the mechanical switch, relay or contactor contact is now in the open state.

[0057] Generally, when a mechanical switch, relay or contactor contact transitions front the open to closed state, the force at which the two contact points hit each other cause them to repel each other thus resulting in repeated opening and closing of the contacts again, and again, i.e., contact bounce. The two terminal arc suppressor of the present invention suppresses contact arcing during contact bounce conditions because a contact bounce consists of a series of contact transitions to the open state and the arc suppressor acts accordingly in the manner already described.

[0058] In addition, due to the optimal and short timing of the firing of the sold state triggerable switch the two terminal arc suppressor is also tolerant of contact chatter during which a mechanical switch, relay or contactor rapidly, successively, and continuously changes between the open and close states.

[0059] FIG. 6 illustrates generally an example of a two terminal arc suppressor 8 mechanical outline. The two terminal arc suppressor 8 is housed in housing 20. Wire terminals 5 and 14 protrude through housing 20 for electrical access and connection to the mechanical switch, relay or contactor single or multi-phase contacts 9.

[0060] It can be seen, then, that the present invention provides a two terminal arc suppressor that is adaptable for use with AC and DC power sources in single or multiphase power systems and that does not require a neutral connection or any external power beyond that which is being switched by a switch, relay or contactor or other contacts are being protected. Having only two wires to contend with, the arc suppressor of the present invention can be quickly installed in that it does not require any additional or other connections to associated or auxiliary equipment. Those skilled in the art will appreciate that the circuits of FIGS. 3 and 4 can be fabricated using solid state, ceramic and thick film technologies only resulting in a device that is rugged and not subject to the failure due to excessive current loads or high operating temperatures.

[0061] In that the circuit is active only during contact transitions, the device undergoes minimal thermal stress on its internal components which is projected to lead to a Mean-Time-Between-Failures (MTBF) in excess of 20 years.

[0062] This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.

[0063] The description of the various embodiments is merely exemplary in nature and, thus, variations that do not depart from the gist of the examples and detailed description herein are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.