AU2005201544A1

AU2005201544A1 - A current limiting system

Info

Publication number: AU2005201544A1
Application number: AU2005201544A
Authority: AU
Inventors: Bernard Boland
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-13
Filing date: 2005-04-13
Publication date: 2006-11-02

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION STANDARD PATENT A CURRENT LIMITING SYSTEM The following statement is a full description of this invention including the best method of performing it known to me: 0 0 A CURRENT LIMITING SYSTEM TECHNICAL FIELD The present invention relates to a current limiting system for limiting mains power current supplied to a load. The present invention has particular, but not exclusive application for use in industrial, commercial and domestic electricity

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S 10 distribution networks 240V, 0 N BACKGROUND Electricity resources are becoming stretched as the population increases so that, in times of peak electricity usage, electricity providers often struggle to cope with consumer demand. Electricity providers often charge consumers higher rates for electricity used in peak periods, with a view of encouraging less electricity consumption at these times. Nevertheless, in the event of a spate of hot weather, a dramatic increase in the usage of electrical appliances such as fans and air conditioning often occurs. The resulting increase in current drawn from the electricity grid has been known to result in the damage and failure of power generation and transmission equipment, in which case blackouts due to electricity grid overload may occur.

Although electricity suppliers can provide additional equipment to cope with peak electricity usage, this equipment is often expensive and is, in reality, only required for relatively short periods of time. In fact, critical electricity peaks typically occur for up to 5% of the time, and additional equipment is neither required not used for the remaining time.

In light of the foregoing problem, it is an object of the present invention to provide a current limiting system which can be used to limit the current supplied to a load. It is a further object of the present invention to provide a system that is well suited for limiting the current supplied at times of peak n electricity usage, and which may also be used to limit the current at other

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o times if required.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a switchable current limiting system for limiting mains power current supplied to a load, the current limiting system including: a switch for connecting between the mains power current supply and the load; S 10 a current limiter connected in parallel to the switch and for, when the Sswitch is opened, supplying the current to the load and limiting the current to Nbelow a predetermined threshold; and a controller for controlling the opening and closing of the switch in response to an actuating signal. During periods of peak electricity usage, the switch may be opened so that the current supplied to the load is limited to below the predetermined threshold.

Preferably, the system further includes: a controller for controlling the opening and closing of the switch in response to an actuating signal. The controller can operate the switch in response to the actuating signal which, in turn, generally depends upon the level of electricity usage peak or off-peak levels of current draw).

Preferably, the system further includes: a receiver adapted to receive a command signal from a conductor which supplies the current to the switch and for generating the corresponding actuating signal. This embodiment enables an electricity provider to remotely operate the current limiting system by sending the command signal over the power supply line. In times of high power usage, the electricity provider can thereby open the switch and limit the current to below a predetermined threshold.

In one embodiment, the current limiter includes a thermal magnetic overload.

SIn another embodiment, the current limiter includes a circuit breaker.

0 0 According to a further aspect of the present invention, there is provided an electricity meter assembly including: an electricity meter for measuring electricity usage; and the switchable current limiting system which is electrically coupled to the electricity meter.

According to a further aspect of the present invention, there is provided a N 10 current limiter assembly for limiting mains power current to a load, the Oassembly including: N a first connection point to receive the mains power current; a second connection point for coupling to a load; a switch disposed between the first connection point and the second connection point; a current limiter connected in parallel to the switch and arranged to limit the current therethough to below a predetermined threshold; and a controller to open the switch in order to limit the current through the second connection point to below the predetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description will make reference to a number of drawings as follows: Figure 1 is a schematic diagram showing an electricity distribution network in which a first embodiment of a current limiting system of the present invention is connected; and Figure 2 is a schematic diagram of a switchable current limiting system in accordance with embodiments of the invention, showing a switch in an open state during a period of peak electricity usage.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to Figure 1. An electricity distribution network 100 includes a power generation plant 102 which generates and supplies main power electricity 240V, 50Hz, single phase) to a household load 104. Current is generated at the power generation plant 102 and then passes through overhead power lines 106 to a household electricity meter 108 which measures the power (and 0 therefore the current) consumed by the household load 104.

0 0 A supply current Is passes from the electricity meter 108 to the household load 104 via a switchable current limiting system 2 according to an embodiment of the present invention. That is, the load current IL supplied to the household load 104 is approximately equal to the supply current Is supplied to the current limiting system 2. With reference to Figures 1 and 2, the current limiting system 2 is housed within a compact housing 110 and includes a circuit breaker 6 which, in turn, has a reset switch 112 that protrudes from the housing 110. The current limiting system 2 is retro-fitted within the meter box 114 of a house, and is connected in series between the existing electricity meter 108 and a main switchboard (not shown) which, in turn, is connected to the household load 104. Any existing circuit breakers, fuses and the like circuit protection of the electricity meter 108 are left in tact.

The housing 110 includes two connection points in the form of electrical connectors A, B for interfacing with the electricity meter 108 (and hence the mains current supply 102) and the switchboard (and hence the load 104) respectively.

Referring to Figure 2, the current limiting system 2 includes a relay switch 4 which is connected in parallel to the circuit breaker 6. The switch 4 is operable between an open open circuited) state as shown in Figure 1, and a closed state (not shown) where a switch current

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sw can pass through the switch 4 to the load 104. The switch 4 is rated to safely carry a maximum current of 40 Amps.

0 The circuit breaker 6 is a type of current limiting device and is rated to 32 N Amps. That is, the circuit breaker 6 can safely carry a current ICB of up to 32 Amps although, when the current exceeds this predetermined threshold, the circuit breaker "trips" and thereby becomes open circuited. Hence, the current passing though the circuit breaker 6 is limited to below the predetermined threshold of 32 Amps.

The current limiting system 2 also includes a controller 14 which controls the 0 S 10 opening and closing of the switch 4 in response to any one of a number of Oactuating signals 16.

The current limiting system 2 further includes a receiver 18 which is electrically coupled to a conductor 20 that supplies electricity to the switch 4.

The receiver 18 is adapted to receive a command signal 22 which is sent along the conductor 20 from the power generation plant 102. The command signal 22 contains command information relating to whether the switch 4 should be in an open or closed state. The receiver 18 is electrically coupled to the controller 14. In the present embodiment, the receiver 18 and controller 14 are provided in the form of a Zellweger T M ripple control circuit.

During periods of peak electricity usage, an electricity provider is able to transmit to the receiver 18, the command signal 22 containing command information to open the switch 4. The controller then generates a corresponding actuating signal 16a instructing the controller 14 to open the switch 4. When the switch is open, IL ICB IS, as the switch current Isw is zero and the current supplied to the receiver 18 is negligible. Therefore, if the household load current IL drawn exceeds the predetermined threshold of 32 A, the circuit breaker 6 will trip and IL will be zero, thereby resulting in a blackout to the house. In this event, a user can turn off some appliances in the house which contribute to the household load 104, and then reset the circuit breaker switch 112 in the meter box 114 so that electricity can once more be supplied to the load 104.

~fl During periods of off peak electricity usage, the electricity provider can send to o the receiver 18, the command signal 22 containing command information to close the switch 4. The controller then generates a corresponding actuating signal 16a instructing the controller 14 to close the switch 4. When the switch 4 is closed, a load current IL can be safely drawn by the load 104, the level of the load current IL being limited by the existing circuit protection in the electricity meter 108. If the circuit breaker 6 is not tripped, IL ICB lsw and 1- therefore in excess of 40 Amps can be drawn by the load 104 via both the circuit breaker 6 and the switch 4. If the circuit breaker 6 is tripped, IL ISW and therefore only up to 40 Amps can be safely drawn by the load 104 via the o switch 4.

The Applicant believes that a suitable predetermined threshold for the circuit breaker 6 is between 70 to 80% of the expected maximum demand of the load 104. A predetermined threshold in this range has been found to minimise consumer inconvenience due to household blackouts while still offering significant protection of the electricity grid.

In further embodiments of the present invention, additional sensing devices may be interfaced to the controller 14 via a connector C of the housing 110.

Each additional sensing device will generate an actuating signal 16 for instructing the controller to operate the switch 4 between closed and open states.

In a second embodiment of the present invention, there may be provided a scheduler 24 for generating the actuating signal 16b in accordance with a time schedule. Periods of peak electricity usage generally occur between the hours of 7 am and 11 pm on weekdays. In the present embodiment, the scheduler 24 sends an actuating signal 16b instructing the controller 14 to open the switch 4 during various intervals of this peak electricity usage period, and to close the switch 4 at all other times. In an alternative embodiment, the scheduler 24 and controller 14 may be contained within a single microprocessor package.

In accordance with a third embodiment of the present invention, there may be o provided an illumination sensor 26 for generating an actuating signal 16c in N accordance with the level of ambient daylight. Generally speaking, the offpeak electricity usage period is during the night and the peak electricity usage period is during daylight hours. The illumination sensor 26 therefore detects whether it is daylight or nighftime, and accordingly generates the actuating signal 16c instructing the controller to open or close the switch 4 respectively.

In accordance with a fourth embodiment of the present invention, there may Nl 10 be provided a thermostat 28 for generating an actuating signal 16d in o accordance with the ambient atmospheric temperature. During periods when Cl the ambient temperature is quite high, residential and industrial electricity usage increases as consumers make use of their air-conditioning. Similarly, during periods when the ambient temperature is quite low, residential and industrial electricity usage increases as consumers make use of their heaters.

These extremes of ambient temperature can effectively form a peak period of electricity use. During this peak time, the thermostat sends the actuating signal 16d to the controller 14 so as to open the switch 4.

A person skilled in the art will appreciate that many embodiments and variations can be made without departing from the ambit of the present invention.

In the first embodiment, the current limiting system 2 was used for limiting mains power current supplying an entire household. In an alternative embodiment, a plurality of current limiting systems 2 may be installed in the meter box 114 for each limiting the mains power current supplied to a respective load of the household load 104.

In the first embodiment, the circuit breaker 6 could be manually reset by a user after it had tripped. In alternative embodiments, the current limiting systems 2 includes sensing equipment for automatically reselling the circuit breaker 6 when the user turns off a number of appliances drawing current (i.e.

loads) within the home.

0 oA person skilled in the art will appreciate that any one of a number of current N limiting devices could be used as an alternative to the circuit breaker 6 of preferred embodiment. For example, the current limiting systems 2 may instead include a thermal magnetic overload (TMO) or other like current limiting device. In an alternative embodiment, the current limiter may cause the load current IL to saturate be clamped) at the predetermined threshold.

0 N 10 In the preferred embodiment, the switch 4 was a relay which was controlled by o the controller 14. In alternative embodiments, the switch may include any one 0 N of a transistor, a field effect transistor (FET), a power MOSFET, a silicon controlled rectifier (SCR) or any other like electronic switching device.

In the preferred embodiment, the main power supply was a single phase supply for a household load 104. In alternative embodiments, the main power supply may be two or three phase supplies suitable for supplying industrial loads used in factories and the like.

The circuit breaker 6 would typically carry a current IcB when the switch 4 is closed during off-peak electricity usage periods. However, in alternative embodiments, a current limiter need not carry current can be open circuited) when the switch 4 is closed.

In an alternative embodiment of the present invention, the current limiting system 2 further includes a remote consumption monitor (RCM) for monitoring the circuit breaker current ICB. The RCM alerts a user when the circuit breaker is tripped short circuited so that IcB is zero), so that the user can then reset the circuit breaker. The RCM may include a personal computer for alerting the user.

In an alternative embodiment, the RCM may include a warning device which plugs into a power point. When the circuit breaker is tripped, the circuit breaker sends a warning signal to the warning device, via the power cables coupled to the power point. The signal indicates that the circuit breaker has

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o been tripped and the warning device alerts the user accordingly. Typically, the RCM has a digital display which displays the circuit breaker current ICB.

In the foregoing embodiments, the switchable current limiting system 2 was retrofitted in series between a conventional electricity meter 108 and a household load 104. In an alternative embodiment, there is provided an electricity meter assembly which includes, within a single housing, an electricity meter 108 which is electrically coupled to the switchable current N 10 limiting system 2.

0 Cl In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims

1. A switchable current limiting system for limiting mains power current supplied to a load, the current limiting system including: cc a switch for connecting between the mains power current supply and the load; a current limiter connected in parallel to the switch and for, when the switch is opened, supplying the current to the load and limiting the current to below a predetermined threshold; and N a controller for controlling the opening and closing of the switch in Sresponse to an actuating signal.

2. A switchable current limiting system as claimed in claim 1, the system further including: a receiver adapted to receive a command signal from a conductor which supplies the current to the switch and for generating the corresponding actuating signal.

3. A switchable current limiting system as claimed in claim 1, the system further including: a scheduler for generating the actuating signal in accordance with a time schedule.

4. A switchable current limiting system as claimed in claim 1, the system further including: an illumination sensor for generating the actuating signal in accordance with the level of ambient daylight. A switchable current limiting system as claimed in claim 1, the system further including: a thermostat for generating the actuating signal in accordance with the ambient atmospheric temperature.

6. A switchable current limiting system as claimed in claim 1, wherein the O o current limiter includes a thermal magnetic overload. ci

7. A switchable current limiting system as claimed in claim 1, wherein the n current limiter includes a circuit breaker.

8. A switchable current limiting system as claimed in claim 1, wherein the switch includes a relay. 0 N 9. A switchable current limiting system as claimed in claim 1, wherein the Scurrent is a single phase current. A switchable current limiting system as claimed in claim 1, wherein the predetermined threshold is between about 70 to 80% of the expected maximum demand of the load.

11. An electricity meter assembly including: an electricity meter for measuring electricity usage; and a switchable current limiting system as claimed in claim 1 which is electrically coupled to the electricity meter.

12. A current limiter assembly for limiting mains power current to a load, the assembly including: a first connection point to receive the mains power current; a second connection point for coupling to a load; a switch disposed between the first connection point and the second connection point; a current limiter connected in parallel to the switch and arranged to limit the current therethough to below a predetermined threshold; and a controller to open the switch in order to limit the current through the second connection point to below the predetermined threshold.

13. A current limiter assembly as claimed in claim 12, wherein the controller is O oresponsive to a receiver arranged to respond to a remotely generated N actuating signal. n14. A current limiter assembly as claimed in claim 13, wherein the receiver is arranged to receive the remotely generated actuating signal through the first connection point. A switchable current limiting system as claimed in any one of claims 1 to and substantially as herein described with reference to the accompanying Sdrawings.

16. An electricity meter as claimed in claim 11, and substantially as herein described with reference to the accompanying drawings.

17. A current limiter assembly as claimed in any one of claims 12 to 14, and substantially as herein described with reference to the accompanying drawings. Dated this 13 th Day of April 2005 BERNARD BOLAND by my attorneys Eagar Buck Patent and Trade Mark Attorneys