Electrical transmission or interconnection systems – Wave form or wave shape determinative or pulse-producing... – With capacitor
Patent
1996-08-14
1998-06-16
Elms, Richard T.
Electrical transmission or interconnection systems
Wave form or wave shape determinative or pulse-producing...
With capacitor
256 10, 361232, H05C 104
Patent
active
057675929
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the field of generation of power electric pulses of low harmonic content suitable for use in the control of fenced livestock; more particularly to circuits for the generation of repetitive pulses having controlled shapes, and has particular but not exclusive application to circuits for energizers for electric fences.
DESCRIPTION OF THE RELATED ART
Wire fences electrified with intermittent pulses of electricity have been in wide use in New Zealand since at least the 1950s. This type of fence is suitable for enclosing livestock on farms, where the portability of such fences has permitted substantial improvements in management practices such as that of break-feeding a paddock to a herd of cows.
In general the power supplies or energizers used with these fences convert a relatively small and steady supply of power into brief impulses of large power (often several Kilowatts) at a high voltage, typically 5KV or more, by (a) the use of slow charging of a capacitor and then its quick discharge through a gas or solid-state switch, and (b) passing the discharge current through a kind of step-up transformer. This order of magnitude of generated pulse power is required in order to cover an entire farm with a single energizer, and to cope with leakage that may occur on days when rain or dew causes insulators to exhibit surface leakage particularly across salt deposits, or when wet grass is in contact with parts of the fence. Energizers may be made to produce anywhere from one or less Joules up to about 25 Joules of energy.
One lead of the transformer secondary is connected to a farm-wide network of usually galvanised iron wires forming various fence lines; the other lead is connected to earth where currents due to leakage and capacitative charging will be found, as well as currents that have passed through animals that inadvertently touch the wire. As the power impulses are widely separated in time an animal or human has time to disengage from the fence wire before a following shock, so these fences are relatively unlikely to cause death, (as compared to a hypothetical arrangement using DC current or AC mains, for example).
In their simplest and oldest forms electric fence energizers are not unlike capacitative-discharge ignition systems for internal combustion engines. An electric fence energizer also resembles a low-frequency radio transmitter in that a source of pulsed electricity is coupled to a long aerial. A disadvantage of a simple form of electric fence energizer is that some proportion of the power driven into the fence (which is a function of proper matching) may be radiated into space as electromagnetic radiation or interference (EMI). This is also known as radio frequency interference or RFI. Past attempts to minimise this radiation, in order to comply with laws relating to EMI generally operate by filtering out harmonics of the basic pulse. The filters involved must handle the power and voltage levels involved, hence they tend to be expensive and may absorb a substantial proportion of useful energy.
There is therefore a need for an improved electric fence energizer which produces less EMI/RFI and preferably one which accomplishes this by means based on never generating interference, rather than by means based on heavy filtering, which must be at high voltage and high power levels, and hence would require high-capacity components.
There is also a requirement to ensure that electric fence energizers revert to a fail-save condition if a fault develops. As one of the main risks is that the main discharging switch, generally a silicon controlled rectifier (SCR) or thyristor, if it becomes faulty, enters a mode in which repeated discharges of powerful pulses may occur even in the absence of a deliberately generated gate pulse, there is a need to include means to minimise stresses on the thyristor(s) in the circuit as well as to detect such a condition and prevent rapidly repeated faults.
SUMMARY OF THE INVENTION
It is an object of the present invention
REFERENCES:
patent: 4114185 (1978-09-01), Gallagher et al.
patent: 4396879 (1983-08-01), Weinreich et al.
patent: 4859868 (1989-08-01), McKissack
patent: 5381298 (1995-01-01), Shaw et al.
Boys John Talbot
Green Andrew William
Woodhead Robert Charles Bryan
Elms Richard T.
Stafix Electric Fencing Limited
LandOfFree
Pulse generator for electric fences does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pulse generator for electric fences, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulse generator for electric fences will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1729383