Electrical transmission or interconnection systems – Wave form or wave shape determinative or pulse-producing... – With capacitor
Patent
1996-08-22
1998-04-21
Elms, Richard T.
Electrical transmission or interconnection systems
Wave form or wave shape determinative or pulse-producing...
With capacitor
361232, 256 10, G08B 1326
Patent
active
057421048
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric fence energizer of the discharge type, i.e. comprising a capacitor, which is charged to a high voltage and is discharged to the primary winding of a transformer, the secondary winding of the transformer providing a very high voltage to the electric fence circuit. The energizer is in particular intended to be operated by the mains supply, that is by the alternating voltage from the public electric energy distribution network.
2. Description of the Prior Art
Various requirements from the authorities restrict the electric voltage pulses which are allowed to be supplied to an electric fence. The conventional requirements in Western Europe are thus that the maximum voltage in each pulse is at most 10 kV over the output terminals of the electric fence energizer, the largest electric current per pulse through a human being or through an animal is allowed to be 10 A, each electric pulse is not allowed to carry more energy than 5 joules, which can be provided to a human being or an animal contacting the electric fence, the pulses are not allowed to come more frequently than one pulse per second and the length of each pulse should be smaller than 1.5 ms and finally that the total amount of charge in each pulse, which can be provided to a human being or an animal contacting the fencing network, should be less than 2.5 millicoulombs. Naturally, all these requirements exist in order to reduce the risk for damages to human beings and animals which contact the electric fence network. However, in order that an electric fence should efficiently limit or deter animals, the pulses provided from the electric fence should both have as large voltage as possible and have as large energy as possible, within the limits imposed by the authorities.
An electric fence considered as an electric circuit, however, presents large variations depending on weather, earthing, and other factors which influence the isolation of the fence wire in relation to the earth or the ground. The resistance of the electric fence to ground can thus for dry weather and otherwise dry exterior conditions with good isolation be very large compared to the condition which can be obtained, when for instance a human being is in contact with the fence, when the resistance can decrease to about 500 ohms. For extreme exterior conditions, in addition, the resistance can decrease to still lower values. The electric fence circuit also comprises a capacitive part which can be important, when the resistance of the fence is large and which can cause that the circuit operates as a swinging circuit owing to the inductance in the transformer winding which supplies the high voltage pulses to the fence circuit. It can result in overswings in the voltage pulse generated on the fence side, which causes that the charge voltage for the capacitor, from which the pulse is discharged, must be reduced in order that the output pulses should not be too high. Then, without a suitable control, a reduced voltage will be obtained also in those cases, when the fence circuit only has an insignificant capacitive component compared to the fence resistance.
A possibility of obtaining an electric fence having a good efficiency is using two transformers, one of which is used for providing high voltage pulses, when the electric fence has a good isolation to earth, also included in this isolation one or several human beings or one or several animals in contact with the fence, and another is used in the case where this isolation is not as good, such as for humid weather. In the latter case, for circuit technical reasons, only smaller voltage pulses can be supplied but they will then instead be given a larger energy content. Alternatively a single transformer having two separate primary windings can be used.
In the British Patent Specification No. 1 395 498 an embodiment of an electric fence device is disclosed, see FIG. 1, having a second primary winding 4. The voltage over this extra winding is used fo
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SEMKO Certificate issued Apr. 15, 1987.
Eriksson Lars-Arne
Karlsson Goran Karl-Olov
Alfa Laval Agri AB
Elms Richard T.
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