AU661841B2 - Surge protector - Google Patents

Description

b6i1~B4l P/00/01i1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: SURGE PROTECTOR 4 44 4 4.

4. 4 44** *t$4 4 4 ;1I~ 4 $4444 I ~u 444 The following statement is a full description of this invention, including the best method of performing it known to us: 44 4 44 4 4 44 GH&CO REF: 04210O-PF RW/SMcL 2 This invention relates to a device for use in protecting electrical equipment against high voltage spikes that occur in supply lines, for example as a result of lightening strikes and switching faults. The device is hereinafter referred to as a surge protector.

Surge protectors are conventionally used to protect electrical equipment such as computers and telecommunications equipment from high voltage spikes that occur in supply lines without functioning to isolate the equipment from the supply. Such protectors are normally used in sophisticated commercial installations and their operation is supervised by skilled personnel who are trained to act promptly in replacing or resetting :protector elements that are damaged or tripped in 15 fulfilling the protective role. Prompt repair and/or *9* replacement is necessary because the equipment to be protected is not isolated from the supply during the time when the surge protectors are inoperative.

The increasing usage of sensitive computer and telecommunications equipment in commercial offices and *domestic dwellings has created a need for a surge Sprotector which is suitable for use in situations where lower levels of supervision exist, and the present invention is directed to such a surge protector.

If t Broadly defined, the present invention provides a surge protector which is connectable to an electrical supply. The surge protector comprises a surge arrestor device which has an impedance that decreases in response to the existence of a high applied voltF?,, means connected in circuit with the surge arrestor device and arranged to respond to a predetermined leel of current flow through the surge arrestor device, a fault condition detector circuit connected in circuit with said means and arranged to be activated in the event of current flow through the surge arrestor device at said predetermined level, and a fault condition indicator associated with the fault condition detector circuit. The surge arrestor device is located within a plug- in unit which is i Ci SS:04210 OPF iJ -3removably mounted to a housing that contains further circuit components of the surge protector.

The housing to which the plug-in unit is mounted may be integrated in or form a part of a switched power outlet of the type that is arranged to receive one or more plugs. Alternatively, the housing may be incorporated in or form a part of a power board of the type that is arranged to be connected to a power outlet and to receive a plurality of plugs. As a further alternative, the housing may form a part of a dedicated surge protector unit.

The fault condition indicator preferably comprises a sound emitter which most preferably is activated in a .4 Smanner such that it cycles on and off. Such sound emitter preferably comprises a Helmholz resonator and is connected in circuit with an oscillator.

The sound emitter is preferably located behind the plug-in unit and the plug-in unit is preferably provided with an opening or grill to facilitate sound emission.

The surge arrestor device preferably comprises a varistor and, most preferably, a metal oxide varistor (MOV), although other devices that exhibit non-linear K 44 1impedance and which function effectively to short-circuit 25 A fuse device is preferably located in series with the surge arrestor device and is selected to open-circuit when a predetermined level of current flows through the surge arrestor device. The fault condition circuit is connected across the fuse (when provided) in such a manner that the circuit is connected across the supply voltage when the fuse is caused to open circuit.

The fuse, when provided, is preferably incorporated in the plug-in unit together with the surge arrestor device.

The invention will be more fully understood from the following description of a preferred embodiment of the surge protector. The description is provided in esw conjunction with the accompanying drawings in which: V r S:0421OPF JIf? 4 Figure 1 shows a front elevation view of a switched power outlet device of the type which is intended to be mounted to a wall and which incorporates the surge protector, Figure 2 shows a sectional end elevation view of the power outlet which is illustrated in Figure 1, the view being taken in the direction of section plane 2-2 as shown in Figure 1, and Figure 3 shows a circuit diagram of the surge protector which is incorporated in the power outlet of Figures 1 and 2.

As illustrated, the surge protector 10 is mounted to a switched power outlet 11 which comprises a facia plate 12, a cover plate 12a (which is shown removed from the facia plate in Figure two plug sockets 13 and two rocker actuated switches 14. The surge protector includes two major components, one of which comprises a casing 15 which is secured permanently to the rear of the facia plate 12 and the other of which comprises a removable plug-in unit 16. The plug-in unit 16 locates within a cavity 17 and is accessed from the front of the facia plate 12.

lThe plug-in unit 16 has a forward face 18 that normally lies flush (or almost flush) with the front of the facia plate 12, and narrow recesses 19 are provided within the facia plate, one at each side of the plug-in t unit 16, to enable the plug-in unit to be prised from the recess 17. The recesses 19 are located behind the cover plate 12a, and a portion of the cover plate is shown broken away in Figure 1 to reveal one of the recesses.

The casing 15 contains electronic components which normally would not be damaged in operation of the surge i ,protector, and the plug-in unit 16 houses electronic components that are or may be damaged when the surge protector operates to arrest transient spikes in the supply voltage. A plug pin 20 which carries three i conductors (not shown in the drawings) is provided for S:04211PF/428 S:04210PF/428 r

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a ~1 k ii I L 1 b effecting electrical connection between the electronic components in the plug-in unit 16 and those in the casing The electronic components that are located within the plug-in unit 16 are shown within the chain-dotted line 21 in Figure 3, and the remaining electronic components that are shown in the circuit diagram of Figure 3 are located within the casing 15. The components that are shown surrounded by the dotted line 22 within Figure 3 form components of a hybrid integrated circuit.

As shown in Figure 3, the surge protector is connected across the active-neutral supply terminals of the power outlet and, in use, in parallel with a load 23.

The surge protector and the load are connected in circuit with the supply when the switch 14 is closed, and the load is maintained in circuit with the supply even when the surge protector is rendered inoperable. Thus, it is important that the surge protector be made operational as soon as possible after it has been rendered inoperable by a transient voltage spike in the supply.

The plug-in unit 16 houses a metal oxide varistor and a series connected fuse element 26. Also, a neon lamp 27 is connected across the varistor 25 and, when energised, provides indication that: a) the varistor 25 has not been damaged to an extent that it comprises a short-circuit, and b) the fuse element 26 has not been fused.

When the plug-in unit 16 (or 21 as shown in Figure 3) is located in position, the fuse 26 functions to short-circuit the input terminals 28 and 29 of an associated fault condition circuit. With the terminals 28 and 29 short-ciz uited by the fuse 26, transistor is turned off and the following transistor 31 is turned on. This in turn causes the voltage at the supply rail 32 to be held low.

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r .i i i S:04210PF/428 6- A Helmholz resonator 33 is connected between the supply rail 32 and earth potential by way of a transistor 34, and the resonator is held inactive when the voltage at the supply rail 32 is low.

The resonator 33 is located within the casing behind the plug-in unit 16. When activated, the resonator emits sound through a sound channel (not shown) within the plug-in unit 16 and then through grid-like S s 34 within the front face 13 of the plug-in unit 16.

Two 7555 I.C. oscillators 35 and 36 are incorporated in the fault condition circuit and are gated off when the voltage at the supply rail 32 is low. Oscillator 35 is controlled by a resistance-capacitance network which is selected to provide 30mS wide pulses at one-second intervals, and the output pulses from the oscillator are employed to gate the following oscillator 36. The oscillator 36 is controlled by a resistance-capacitance network to provide a 2,800Hz output during the S.o. gating period.

The output from the oscillator 36 is used to turn on .r the transistor 34, so that the resonator provides a ,2,800Hz audible signal for 30mS during each one-second Sinterval.

The audible signal from the resonator 33 is generated when the fuse element 26 is fused and, thus, the input terminals to the fault condition circuit are j connected across the supply voltage. That is, when the fuse element 26 is fused and the supply voltage appears t across the input terminals 28 and 29, transistor 30 is 30 switched on and transistor 31 is switched off. With transistor 31 switched off the voltage at the supply rail 32 goes high, this providing excliation voltage for the resonator 33 and providing for gating of the two oscillators 35 and 36.

In the absence of any transient spikes in che supply voltage, the varistor 25 maintains a high impedance and S:04210PF/428 7 an insignificant current flows through the fuse element 26. The fuse then remains intact, the neon indicator lamp 27 is energised and the resonator 33 is not activated. However, should a spike of sufficient magnitude appear in the supply, the full voltage will appear across the varistor 25 and cause the characteristic drop in impedance in the varistor. The resultant current flow through the varistor will cause fusing of the fuse element 26, and the supply voltage will then appear across the input terminals 28 and 29 of the fault condition circuit. This then causes activation of the alarm in the manner described above.

i :04 S:04210PF/428

Claims (10)

1. A surge protector which is connectable to an electrical supply and which comprises: a surge arrestor device which has an impedance that decreases in the presence of a high applied voltage, means in circuit with the surge arrestor device arranged to respond to a predetermined level of current flow through the surge arrestor device, a fault condition detector circuit connected in circuit with said means and arranged to be activated in response to said predetermined level of current flow through the surge arrestor device, and a fault condition indicator in circuit with the fault condition detector circuit, the surge arrestor device 0, being located within a plug-in unit which is removably S15 located within a housing that contains further circuit ee components of the surge protector. reou

2. The surge protector as claimed in claim 1 wherein the housing to which the plug-in unit is removably mounted forms a part of a switched power outlet 20 of a type that is arranged to receive at least one electrical power connector plug

3. The surge protector as claimed in claim 1 t wherein the housing to which the plug-in unit is removably mounted forms a part of a power board of a type that is arranged to be connected to a power outlet and to receive a plurality of electrical power connector plugs.

4. The surge protector as claimed in any one of claims 1 to 3 wherein the fault condition indicator includes a sound emitter which is activated following a predetermined increase in current flow through the surge arrestor device.

The surge protector as claimed in claim 4 wherein the sound emitter comprises a Helmholz resonator connected in circuit with an oscillator.

6. The surge protector as claimed in claim p wherein the sound emitter is located within the housing behind the plug-in unit and wherein the plug-in unit is ie i provided with a passage to facilitate radiation of sound :421OPF i~lS:O20PF 9 from the emitter.

7. The surge protector as claimed in any one of the preceding claims wherein the surge arrestor device comprises a metal oxide varistor.

8. The surge protector as claimed in any one of claims 1 to 7 wherein said means in circuit with the surge arrestor device comprises a fuse located in series with the surge arrestor device, the fuse being rated to open-circuit when the predetermined level in current flows through the surge arrestor device and the fuse being located in the plug-in unit together with the surge arrestor device.

9. The surge protector as claimed in claim 8 wherein the fault condition detector circuit is connected 15 across the fuse in a manner such that the fault condition detector circuit is connected across the electrical supply when the fuse is caused to open-circuit.

10. The surge protector substantially as shown in the accompanying drawings and substantially as S. 20 hereinbefore described with reference thereto. *1a DATED this 2nd day of June 1995 i H.P.M. INDUSTRIES PTY LIMITED By their Patent Attorneys GRIFFITH HACK CO -t S:0421 PF r_ ABSTRACT A surge protecto which is connectable to an t electrical supply and which comprises a surge arrestor in the tirm of a metal oxide varistor which is connected in 5 circuit with a fault condition detector circuit. The fault condition detector circuit includes a fuse which is located in series with the surge arrestor device, and a fault condition indicator, which includes a sound emitter, is located in circuit with the fault condition detector circuit. The surge arrestor device and the fuse are both located in a plug-in unit which is removably t mounted to a housing that contains the remaining elements of the surge protector. e i S:04210PF/428 -L 1 L_ r i-