NZ280910A - Residual current device switch mechanism; welded contacts separable by force applied to manual reset button - Google Patents

Description

Jftdflf thO PfC1.. of Re$19- 'ii&Oft 23 (1) the %W"Ci;'!Ciit«on has e~: ?-<ir.'u4 » (te.sJtoj. 280910 Inifeds ' 24*i ;Prig^y Date(s): ;Complete Specification Filed: .?{?.!.?. ;ClrasA6)..BoLH.O./.P.?.f..,.±i ;Publication Date:<....2...ll...4il.l:..1935.. ;P.O. Journal No: * Lhfr.9.k.. 3 0 JAN 1395 received NEW ZEALAND PATENTS ACT, 1953 Divisional from New Zealand Patent No. 239076/242376 COMPLETE SPECIFICATION Switch Mechanism We, PDL HOLDINGS LIMITED, a New Zealand company of 14 Hazeldean Road, Christchurch, New Zealand do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 2809 1 This invention relates to a switch mechanism and more particularly to a residual current device (RCD) incorporating the mechanism.

An RCD is a safety device which cuts power to an electrical appliance or other load in the event of certain faults. The device senses current imbalance between active and neutral power conductors resulting from earth currents created by the faults. A differential transformer generates an out of balance signal which is electronically amplified and compared with a predetermined threshold. Exceeding the threshold disables a switch mechanism and opens a contact set to cut the power.

A switch mechanism and RCD incorporating the switch mechanism are described and claimed in New Zealand Patent specification No. 239076/242376 of which the present specification is a divisional.

For the effective operation of the RCD it is important to ensure the contact sets apart correctly. In some fault conditions the contacts may become tack welded together.

It is an object of the present invention to provide a switch mechanism for RCDs which will overcome this difficulty.

Accordingly the invention consists of a switch mechanism in which a contact set has a moveable contact carried on a contact carrier; wherein a manual reset means is operable to displace the contact carrier to a position from which the contact carrier can pivot and close the contact set in the sense of an earth fault, or, should the contacts become tack welded together, to a position from which an increasing manual force can be applied through the manual reset means to pivot the contact carrier and break the contact apart. hi a further aspect die invention may be said to consist in a residual current device incorporating a switch mechanism according to the preceding paragraph.

General principles of the invention and preferred embodiment will be described with reference to the accompanying drawings of which: Figure 1 is a diagrammati c representation of the switch mechanism with the contact set closed; Figure 2 shows the beginning of an under voltage release of title contact carrier from the first fulcrum position; Figure 3 shows movement of the carrier to pivot about the second fulcrum position; Figure 4 shows the contact set open; Figure 5 shows the beginning of a reset operation in an under voltage condition; Figure 6 shows the reset operation nearly complete in a normal voltage condition; Figure 7 shows die switch mechanism and an indicator with the contact set closed; 260910 Figure 8 shows the indicator of Figure 7 with the contact set open; Figure 9 is an example RCD circuit which may incorporate the switch mechanism; Figure 10 is a side view of a preferred RCD with the contacts closed; Figure 11 is a section of the RCD in Figure 10; Figure 12 is a side view of the preferred RCD with the contacts open; Figure 13 is a section of the REC in Figure 12; Figure 14 is an underside view of the preferred RCD; Figure 15 is an overhead view of the preferred RCD; Figure 16 is an end view of the preferred RCD; and Figure 17 is an isometric view of the lever assembly and a differential transformer in the preferred RCD; Referring to these drawings, Figures 1 to 8 are intended to demonstrate the general principles of a switch mechanism according to the invention/Figures 9 to 17 show how a preferred embodiment of the mechanism may be incorporated in an RCD. The switch is normally open until mains power is applied to energise an electromechanical device such as a solenoid. Manually operating a reset device, such as a push button, then closes the contact set and provides power to a load. If mains power is removed or if a control circuit detects an out of balance current flow, the solenoid is de-energised to trip a lever system and the contacts spring open.

As shown in Figures 1 to 6, the contact set comprises a fixed contact 1 mounted on an appropriate support and a moveable contact 2 mounted on a contact lever or contact carrier 3. The moveable contact carrier is able to pivot about either of a first fulcrum position 4 on swing aim 5 or a second fulcrum position 8 on the support. Spring 9 provides a force on the carrier between the fiilcrums and causes the pivoting when required to open or close the contacts. A sufficient voltage applied to solenoid 6 holds plunger 7 from acting on arm 5. On an under voltage condition the plunger is released to impact arm 5 to disengage fulcrum 4 from carrier 3 and allow the carrier to pivot about fulcrum 8. Button 10 is mounted on the support and pushes on carrier 3 through shaft 101 to move the carrier away from fulcrum 8 and allow pivoting about fulcrum 4 in resetting the mechanism. Arms 42 and 43 extend from carrier 3 and arm 5 respectively, and interact to restore the plunger within the solenoid during pivoting of the carrier about fulcrum 8.

Referring to Figure 1, the contact set is shown closed in a no fault working condition of the switch. Spring 9 pushes one end of carrier 3 against fulcrum 4 and at the other end contact 2 is pushed against contact 1. There is a clearance between carrier 3 and fulcrum 8. Plunger 7 is held in solenoid 6 against a bias spring by a voltage derived from 2609 10 the mains with a gap to arm 5.

Referring to Figure 2, initial movement of the mechanism is shown on occurrence of a fault The voltage is solenoid 6 has been dropped and plunger 7 is ejected by the bias spring to impact and deflect swing arm 5. This disengages fulcrum 4 from carrier 3.

Continuing the movement as shown in Figure 3 opens the contact set. Spring 9 pushes carrier 3 towards fulcrum 8 about which the carrier pivots. This separates the contacts breaking current to the load. Arms 42 and 43 have moved together.

In Figure 4, the contact set is shown fully open. Carrier 3 has pivoted to maximum about fulcrum 8. Arm 42 on carrier 3 has pushed arm 43 on swing arm 5 past the position of Figure 1 and restored plunger 7 within the solenoid. The action reduces the size and cost of the solenoid required. The plunger is pushed against the solenoid bias spring indirectly by spring 9.

Referring to Figure 5, a reset operation is shown attempted with the solenoid de-energised. For example, there may be low mains voltage or an active or neutral open circuit on the line side of the contacts. Arm 42 is omitted for clarity. As button 10 reciprocates, shaft 101 pushes carrier 3 away from fulcrum 8 against spring 9. Plunger 7 is correspondingly released from solenoid 6 deflecting swing arm 5 so that fulcrum 4 cannot engage the carrier. This simply returns the mechanism to the state of Figure 4 on releasing the button.

In figure 6 a reset becomes possible as the solenoid is energised by a normal voltage. On pushing carrier 3 away from fulcrum 8, plunger 7 now remains held in soleL oid 6. The carrier 3 slides over fulcrum 4 and swing arm 5 is maintained in a position for their engagement Pressure on button 10 is removed and spring 9 pushes carrier 3 to engage fulcrum 4 at one end, followed by pivoting to close the contact set. This returns the mechanism to the state of Figure 1. In an RCD if a fault on the load side remains, the solenoid will be de-energised and the switch will immediately trip after resetting.

Figures 7 and 8 show a means which indicates whether power is being supplied to the load. An arm 11 is mounted on carrier 3 and carries a flag 12 which is visible in opening 13 when contacts 1 and 2 are closed. On a fault the carrier 3 pivots to open the contacts and moves the flag to a less visible position, making it apparent that the fault has occurred.

Figure 9 shows a control circuit which could be used with the switch mechanism of Figures 1 to 8 in an RCD. This is based on a Raytheon RV4145 ground fault interrupter integrated circuit 2ti. A differential toroidal transformer 15 has mains active and neutral conductors 16 and 17 passing centrally through a core over which is wound a secondary 260910 winding 18 of high inductance. The conductors are effectively anti-phased primary windings such that normal load currents cancel each other resulting in zero output voltage from the secondary winding. An output voltage is developed when a small residual current from the load active flows back to line neutral indirectly, usually via ground, from a faulty appliance or cable connected in the load.

A metal oxide varistor 34 is provided to limit peak mains transients from causing damage to the circuit or any attached appliance. Power is supplied to the circuit by a half wave rectifier 35 and current limiting resistor 36. Capacitor 33 is charged and applies a voltage to solenoid 6 which retains plunger 7 so that contact 1,2 can be closed. Action of the plunger in the switch mechanism is indicated by the dashed line. As IC 20 draws veiy little quiescent current, resistor 37 is used as a simple voltage dropper, with capacitor 38 provided as a precaution against electrical noise problems rather than as a supply filter.

One end of coil 18 is connected to IC 20 at pin 3 which is a common amplifier reference point Capacitor 19 filters high frequency noise from the secondary voltage, while capacitor 22 provides noise bypassing from die bulk of the coil to IC 20 at ground pin 4. The active end of coil 18 is connected to an amplifier summing junction at pin 1 through capacitor 25 and resistor 26. Resistors 27 and 26 determine the amplifier gain while capacitor 25 series resonates with the coil inductance and is designed to extract mains frequency signal components from loads which use half wave power control. Otherwise the core would saturate from the resulting DC and product very little output to trip the switch. Capacitor 28 provides amplifier high frequency roll off.

The amplifier output is internally connected to comparators which are referenced to zener diodes in IC 20. When the amplified signal detected on pin 1 exceeds the zener thresholds, an output signal at pin 5, filtered by a capacitor 30, triggers a silicon controlled rectifier 31. The SCR 31 latches via the current limiting resistor 32 and temporarily discharges capacitor 33 creating an under voltage condition on solenoid 6. This releases plunger 7 to cause opening of the contacts, turning off power to the load. Capacitor 33 then recharges to allow closing of the contacts in a reset operation.

A circuit test means is provided by which unbalanced current is passed through the transformer core to check action of the switch. Button 14 is pressed td complete a link between the active and neutral conductors, taking a portion of the active current determined by resistor 39 through die transformer twice. This simulates a residual current flowing from the neutral conductor and escaping to earth.

Figures 10 and 17 show a preferred switch mechanism using the principles outlined with respect to Figures 1 to 8, incorporated in an RCD. Most of the circuit components 260910 outlined with respect to Figure 9 have been omitted for clarity. The RCD structure is built around a printed circuit board 50 and plastics casing elements 51, 52 clipped together at 53, 54, 55. Using references as in Figures 1 to 8 the structure comprises two pairs of contacts 1 and 2 moveable contact leva: 3, moveable contact carrier first fulcrum means 4 on swing arm 5, solenoid 6 and plunger 7, second fulcrum means 8, pivoting spring 9, reset means 10, extensions 42 and 43 on carrier 3 and aim 4 respectively, indicator arm 11, flag 12 and view opening 13. This structure also shows spring 70 which ejects plunger 7 from solenoid 6 and spring 71 which ensures proper latching of fulcrum 4 on lever 3. Using references as in Figure 9 the structure comprises differential transformer 15, active and neutral conductors 16, 17, test means 14 and conductor 40. In fixing the RCD between mains and a load, the conductors are connected at terminals 60, 61 and 62, 63 respectively.

Referring to Figures 10 and 11 the RCD is shown with the contact pairs closed. The mains active line would be connected to terminal 60 so that current flows through contacts 1, 2 a plate 85 (shown in Figure 17), conductor 16 and terminal 61, from there to the load. The mains neutral line and load are similarly connected on die other side of die device which appears identical. End 80 of the contact carrier 3 is engaged by fulcrum 4 under force from spring 9. Fulcrum 8 have two slots 90 acting as limiting means which loosely receive axles 81, 82 of the contact carrier which acts as locating means. The search fulcrum 8 is formed by abutment between the axles and the end of the slots. Plunger 7 is held to block 73 within solenoid 6 against spring 70 with a gap to aim 5 by a voltage derived from the mains. Flag 12 is apparent in opening 13.

Referring to Figures 12 and 13 the RCD is shown tripped with the contact pairs open. Contacts 1 and 2 are separated to interrupt current flow to the load. End 80 of the contact carrier 3 has disengaged from fulcrum 4, and axles 81, 82 (shown in Figure 17) are engaged in slots 90 on fulcrum 8 under force from spring 9. Plunger 7 was released to impact and deflect arm 5 after de-energisation of the solenoid but is shown restored after action of extension 42 on extension 43. Flag 12 is no longer apparent through opening 13.

Referring to Figures 14 and 15 the RCD underside and topside are shown as they appear with the contacts closed. Current passes through terminals 60, 62, plates 85, 86 on contact carrier 3, conductors 16, 17 and terminals 61, 63 as can be seen. Solenoid 6 is energised to hold plunger 7. Flag 12 is apparent through opening 13.

Referring to Figure 16 an end view of the RCD shows conductors 16,17 passing through differential transformer 15, and also an inside view of test button 14. Pushing the 28 0 9 1 0 button takes a predetermined portion of mains current across contact bar 100 and along conductor 40 through the transformer to simulate a fault.

Referring to Figure 17 the contact carrier 3 and differential transformer 15 are shown separated from the RCD. The carrier supports movable contacts 2 and plates 85, 86 through which the contacts are connected to conductors 16, 17. Indicator arm 11 and flag 12 are centrally placed between axles 81, 82 which engage fulcrum 8 in Figures 10 and 12. Extension 42 is an inverted pocket which engages one end of spring 9 in Figures 11 and 13. When the RCD is being set, two rods 101 from button 10, only one of which is shown in Figures 11 and 13, are pushed down to engage dimples 83, 84. This depresses the entire moveable contact carrier against spring 9 and allows end 80 to engage fulcrum 4 provided the solenoid is energised.

Figures 12 and 17 also show a third fulcrum means 150 as a protrusion on one end of lever or carrier 3 opposite the moveable contacts 2. Contacts 1 and 2 are occasionally tack welded together by a current surge and may be forced apart by the manual reset button 10. On depressing the button as shown in Figure 5 the protrusion 150 eventually meets the casing 52 shown in Figure 10 and 12, and acts as a stop or pivot point for further force applied to the lever or carrier 3 through rod 101 to act on the joined contacts. A considerable manual force may thereby be applied to break the tack weld and open the contacts if necessary. 28 09 1

Claims (4)

WHAT WE CLAIM IS:

1. A switch mechanism in which a contact set has a moveable contact carried on a contact carrier; wherein a manual reset means is operable to displace the contact carrier to a position from which the contact carrier can pivot and close the contact set in the absence of an earth fault, or, should the contacts become tack welded together, to a position from which an increasing manual force can be applied through the manual reset means to pivot the contact carrier and break the contacts apart.

2. A switch mechanism as claimed in claim 1 including a stop against which a portion of the contact carrier abuts when displaced by the manual reset means to form a lever system when breaking the contacts apart with the manual reset means acting on the contact carrier between an end portion which abuts the stop and an end portion which carries the moveable contact.

3. A switch mechanism as claimed in claim 1 or claim 2 when constructed arranged and operable substantially as herein described with reference to the accompanying drawings.

4. A residual current device incorporating a switch mechanism as claimed in any one of the preceding claims when constructed arranged and operable substantially as herein described with reference to the accompanying drawings. By the authorised agents A J PARK & SON