NZ548876A - Improvements in and relating to electric fence systems - Google Patents

Abstract

An electric fence installation with an earth return wire (8) and a protective alternate current path is disclosed. An electric fence energiser (1) has at least three output terminals (4, 5, 9), where two or more of the terminals are earth terminals (4, 9). At least one of the earth terminals provides a protective impedance (10) which reduces the flow of current through that terminal relative to that which may flow through the other earth terminal(s). The shock received by an animal (11) when the shock path (12) is through the earth wire return system can be limited, but still effective, while the shock is not reduced when the shock path does not include the earth wire return system but is through a traditional ground return.

Description

K 548876 *10054164281* PATENTS FORM NO. S Fee No. 4: $250.00 PATENTS ACT 1953 COMPLETE SPECIFICATION After Provisional No: 548876 Dated: 30 August 2006 'i IMPROVEMENTS IN AND RELATING TO ELECTRIC FENCE SYSTEMS WE Gallagher Group Limited, a New Zealand company of Katiikatea Drive, Hamilton, New Zealand hereby declare the invention for which I/We pray that a patent may be granted to me/us, and the method by which it is to be performed to be particularly described in and by the following statement: fL d mooooo^z 'ON/of :ai 'isxfrfr aoos env(nHi) INTELLECTUAL PROPERTY OFFICE OF N.Z. 3 0 AUG 2007 E1.V.£P.

M»s | |eg HOUd 548876 Received at IPONZ on 28/11/2008 IMPROVEMENTS IN AND RELATING TO ELECTRIC FENCE SYSTEMS TECHNICAL FIELD This invention relates to improvements in and relating to electric fence systems. Specifically the present invention may provide improvements within electrified 5 agricultural fences where the electric fence installation incorporates an earth return wire commonly used in environments where the ground is dry and has a low conductivity.

BACKGROUND ART Electrified fences are widely used in agriculture for confining animals within specified 10 areas and from preventing animals from entering specified areas.

Where electric fences are used close to a farm house there is more likely to be human contact with the fence. It is sometimes desirable to reduce the energy available to the electric fence in that area. This is currently achieved by either using a low power output terminal from an electric fence energiser which incorporates a 15 limiting resistor or by placing an external resistor between the high power terminal of the electric fence energiser and the local fence that needs to be energised.

In dry conditions where there is the need for improved earthing such as in Australia there is often used an electric fence installation system called an earth wire return system. In an Earth wire return system some of the wires on the fence are electrified 20 and some of the wires (usually alternate) on the fence are earthed. The earth wire of the fence usually runs all the way back to the ground terminal of the energiser. This provides a low impedance path back for return currents which run back through the earth return wire to the energiser. The earth wire is often grounded at local points along the fence line with earth stakes which are driven into the ground.

When an animal touches both the live fence wire and the earth return wire then the animal will receive a larger shock than in a ground return installation which is the Page 1 548876 Received at IPONZ on 28/11/2008 reason this kind of installation exists. Also when an animal touches the fence and the ground close to a local earth stake the electric current flowing through the animal flows back up the local earth stake along the earth return wire and back to the earth terminal.

In these situations if a person touches both the fence wire and the earth return wire they will receive a larger shock than would ordinarily be felt in a ground return installation due to the low impedance of the earth return wire. Some European countries are concerned at the level of shock available from this kind of installation.

Safety standards are written around a shock received by an animal constituting a 500 10 ohm load and there is wide acceptance surrounding the safety of a shock at this load.

It has been suggested that a shorter body path which may occur where a person climbs between two wires may result in a lower impedance and therefore higher energy shock for this kind of installation.

If the entire farm using an earth wire return system is powered from a low shock 15 terminal then the level of shock available at long distances from the farm will be inadequate to control farm animals.

Accordingly the present invention addresses this problem or at least offers the public a useful choice.

It would therefore be preferable to have an improved method, system or apparatus 20 which addressed any or all the above problems associated with existing prior art earth wire return electric fence systems. In particular a system, method or apparatus which could provide an alternative current path for shocks between firstly live wire and ground return shocks and secondly live wire and earth return wire shocks would be of advantage.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference Page 2 548876 Received at IPONZ on 28/11/2008 constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission 5 that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive 10 meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

Further aspects and advantages of the present invention will become apparent from 15 the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided an electric fence energiser which includes, an electric fence impulse generator having two or more poles configured to emit 20 electric impulses, at least three terminals, two or more of which are configured to be connected as earth terminals and one or more of which are configured to be connected as a fence terminal for the attached electric fence system characterised in that the internal or source impedance of the energiser through one of the earth terminals is higher than 25 the impedance of the energiser through the other earth terminal or terminals.

According to a further aspect of the present invention there is provided an electric Page 3 548876 Received at IPONZ on 28/11/2008 fence energiser which includes, an electric fence impulse generator having two or more poles configured to emit electric impulses at least three terminals, two or more of which are configured to be connected as earth 5 terminals for the attached electric fence system and one or more of which are configured to be connected as fence terminals characterised in that there is a protective impedance connected between one earth terminal and one pole of the impulse generator and there is a direct or lower impedance connection back to the same pole of the impulse generator through one of the other earth terminals In a further preferred embodiment the protective impedance will be a resistance This should not be seen as limiting as in alternative embodiments the protective impedance could be an inductance or a capacitance or a non linear component such as a voltage dependent resistor or a diode or a gas discharge tube.

Preferably the protective impedance will be in the range of 50 ohms to 1000 ohms 15 depending on the degree of reduction in energy that is required by connection to the protective impedance powered earth terminal.

In an alternative embodiment the protective impedance powered earth terminal will be connected to a separate winding on the output transformer of the impulse generator.

In a further alternative embodiment the protective impedance terminal will be 20 connected to a tapping of the output transformer of the impulse generator.

According to a further aspect of the present invention there is provided an electric fence energisation system which includes an electric fence impulse generator having two or more poles configured to emit electric impulses at least three terminals, two or more of which are configured to be connected as earth Page 4 548876 Received at IPONZ on 28/11/2008 terminals and one or more of which are configured to be connected as a fence terminal for the attached electric fence system wherein the impedance back to the impulse generator through one of the earth terminals is higher than the impedance back to the impulse generator from the other earth terminal or terminals.

Characterised in that the earth wire from an earth wire return system is connected to the earth terminal with the protective impedance connected between it and the impulse generator and an earth wire connected to ground stakes in the ground is connected to the earth terminal with a direct connection or lower impedance connection back to one of the poles of the impulse generator.

The configuration of multiple earth terminals provides for alternative return paths for electrical current flowing out through the fence wire through an animal touching the fence and either the ground or a ground return conducting wire or both.

In a further preferred embodiment the impulse generator provided may be formed from an electric fence energiser which includes a transformer with two or more poles 15 to connect to the earth terminals and to the fence terminals however in other embodiments where the impulse generator does not include an output transformer the invention is equally applicable.

In such embodiments the energy storage element provided within a impulse generator may be switched through an energy transfer device such as a transformer 20 or directly onto an electric fence conductor.

The present invention is configured to provide an energisation system for preferably an earth wire return electric fence system .

Also the present invention is configured to provide an energisation system for a combined installation which includes both an earth wire return system and a ground 25 earth return system.

Preferably the impedance connecting the two alternative earth terminals will be a Page 5 548876 Received at IPONZ on 28/11/2008 resistance and the value of that resistance will be between 50 and ohms and 1000 ohms.

However these values should not be seen as limiting as the values can be selected based on any requirement of energy limitation combined with the energy delivering 5 capabilities of the impulse generator.

In a further preferred embodiment the impedance may be a capacitor or an inductor that has an effective impedance of between 50 ohms and 1000 ohms when an electric fence electric impulse is applied across it.

In a further preferred embodiment there may be a voltage measuring or current 10 measuring circuit monitoring the voltage across or current through the impedance connected between the two earth terminals.

This allows the energiser to determine whether the current returning from the fence is coming through the earth wire return path or the ground return path. This indicates whether the load is connected between the fence and earth return wire or between 15 the fence and the ground.

The energiser circuitry may signal an alarm or modify the energisers output in response to the differences in the sensed signal. For example the energy available at the output terminals may be reduced for a period of time when the current through the protective impedance increases above a predetermined threshold or above a 20 predetermined current change or maximum current through the protective impedance, this being an indication that an animal has received a shock between the fence wire and the earth return wire. Alternatively the interval between impulses may be increased for a period of time or the impulses may be stopped altogether for a predetermined period of time before normal operation is resumed in response to a 25 change in the abovementioned sensed signal.

Page 6 548876 Received at IPONZ on 28/11/2008 BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 illustrates the current flow for an animal getting a shock in an earth wire return system with the connections to the impulse generating device provided in accordance with a preferred embodiment of the present invention, and Figures 2 illustrates the current flow for an animal getting a shock through a ground earth return path in an earth wire return system with the connections to the impulse generating device provided in accordance with a preferred embodiment of the present invention Figure 3 illustrates the sensing of the current flowing through the protective earth impedance which shows how a load connected between the fence wire and the earth wire return can be monitored and some controlled action taken in response to any change in this monitored load.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 illustrates a schematic diagram of an electric fence energisation system provided in accordance with a preferred embodiment of the present invention.

The Energiser system shown includes an output impulse generating means 1 which Page 7 548876 Received at IPONZ on 28/11/2008 supplies a high voltage impulse between separate poles 2 and 3. Pole 3 is connected to earth terminal 4 and pole 2 is connected to terminal 5. Terminal 5 is connected to an electric fence wire 6, which is insulated from the ground and from electric fence mounting posts 7 by a post mounted insulator (not shown). An earth return wire 8 is 5 shown which returns to be attached to the energiser's second earth terminal 9 and is electrically connected to the second pole (3) of the impulse generating means 3 through a protective impedance 10 .

When an animal 11 touches both the electric fence wire 6 and the earth return wire 8 an electric current flows out of terminal 5 onto the fence wire 6 through the animal 11 10 and back through the earth return wire 8 back to terminal 9 and through protective impedance 10 back to the second pole 3 of the output impulse generator 1.

The path of the current flow is shown as dotted line 12.

Referring to figure 2, when an animal 11 standing on the ground 14 touches electric fence wire 6 an electric current flows out of one pole 2 of the impulse generator 1 15 through fence terminal 5 through fence wire 6 and through the animal 11. The electric current flows back through the ground 14 to the earth stake system 13 and back into the Earth terminal 4 and back to the second pole 3 of the impulse generator 1. The current path is shown by the dotted line 12.

In this case the shock the animal receives is limited by characteristics of the impulse 20 generator and further limited by the impedance of the ground, the connection of the animals feet to the ground, the impedance of the ground back to the earth stake system 13 and the contact impedance from the earth stakes to the ground.

The advantage of this invention is that an earth wire return system can be used where the shock received by an animal completing a circuit through the earth wire return 25 system can be limited (but still effective) while not reducing the shock received by an animal where the shock path does not include the earth wire return system but is through the traditional ground return system.

Page 8 548876 Received at IPONZ on 28/11/2008 In a further preferred embodiment of the invention a monitoring circuit monitors the current through or voltage across the protective earth impedance and activates an alarm and or modifies the output of the impulse generator depending on the result of 5 the monitored signal.

Referring to Figure 3 there is shown an animal 11 contacting both the fence wire 6 and the earth return wire 8. The current flows out of the impulse generator 2 and along fence wire 6 through the animal 11 and back through the earth return wire 8 back through Earth wire system connection terminal 9 and through protective earth 10 impedance 10 back to the second pole 3 of the impulse generator 1. Monitoring circuitry 13 monitors either the current through or voltage across protective impedance 10. The monitoring and control circuitry 13 may activate an alarm 14 or modify the output from the impulse generator 1 in response to the detection of an increase in current through or voltage across protective impedance 10 which is 15 indicative of a change in state or load of the fence system when for example an animal becomes entangled and in contact with the fence and earth return wire.

A further advantage of the invention is that when there is a short circuit between the fence and the earth return wire then the output voltage across the two poles of the impulse generator will not fall below the voltage that the impulse generator can 20 sustain across the equivalent value of the protective impedance which is connected between the two earth terminals.

This means there is still a deterrent voltage between the fence wire and the ground or between the earth return wire and the ground.

In this way the shock an animal receives with an earth return wire connection can be 25 limited by the value of the protective impedance 10 while still maintaining an effective fence when an animal receives a shock where the animal contacts the electric fence wire and the ground.

Page 9 548876 Received at IPONZ on 28/11/2008

Claims (1)

WHAT WE CLAIM IS:

1. An electric fence energiser which includes at least three output terminals where two or more of the terminals are configured as earth terminals and at least one of the earth terminals is adapted to provide a protective impedance of less than 1000 ohms which reduces the flow of current through that terminal relative to that which may flow through the other earth terminal or terminals. 2 An electric fence energiser as claimed in claim 1 where the protective impedance is a resistor. 3 An electric fence energiser as claimed in claim 1 where the protective impedance is a capacitor. 4 An electric fence energiser as claimed in claim 1 where the protective impedance is an inductor. 5 An electric fence energiser as claimed in claim 1 where the protective impedance is a non linear device. 6 An electric fence energiser as claimed in claim 6 where the non linear device is a voltage dependent resistor. 7 An electric fence energiser as claimed in claim 6 where the non linear device is a gas discharge tube. 8 An electric fence energiser as claimed in claim 1 where the protective impedance is achieved by a connection to a tapping of an output transformer. 9 An electric fence energiser as claimed in claim 1 where the protective impedance is an impedance connected between one of the earth terminals and a second of the earth terminals. Page 10 548876 Received at IPONZ on 28/11/2008 10 An electric fence system where an earth return wire is connected to the impedance protected earth terminal of an energiser as claimed in any previous claim. 11 An electric fence system where a ground stake earth system is connected to an earth terminal connected directly to a pole of an impulse generator and an earth return wire is connected to a second earth terminal which has a protective impedance between the second earth terminal and the pole of the impulse generator. 12 An electric fence energiser as claimed in any claim from 1 to 9 which includes an impulse generator where a current signal through the protective impedance is monitored. 13 An electric fence energiser as claimed in claim 12 where the output energy from the impulse generator is modified in response to a change in the current signal monitored through the protective impedance. 14 An electric fence energiser as claimed in claim 12 where an alarm is activated in response to a change in the current signal monitored through the protective impedance. 15 An electric fence energiser as claimed in claim 12 where the pulse interval of pulses emitted by the impulse generator is modified in response to a change in the current signal monitored through the protective impedance. 16 An electric fence energiser as claimed in any claim from 1 to 9 which includes an impulse generator where the voltage signal across the protective impedance is monitored. 17 An electric fence energiser as claimed in claim 16 where the output energy from the impulse generator is modified in response to a change in voltage monitored across the protective impedance. Page 11 548876 Received at IPONZ on 28/11/2008 18 An electric fence energiser as claimed in claim 16 where an alarm is activated in response to a change in voltage monitored across the protective impedance. 19 An electric fence energiser as claimed in claim 16 where the impulse interval of impulses emitted by the impulse generator is modified in response to a change in voltage signal monitored across the protective impedance. Page 12