GB2115994A

GB2115994A - Electrical supply systems

Info

Publication number: GB2115994A
Application number: GB08305648A
Authority: GB
Inventors: James John Goodman
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-01
Filing date: 1983-03-01
Publication date: 1983-09-14
Also published as: GB8305648D0

Abstract

An electrical supply system 10 comprises a three phase supply busbar 11, which is contained in electrical trunking (22, Figure 2). Each length of trunking has at least one tapping point 12, with an associated socket and lamp 14 and a triac 17, which controls the supply of power to the socket. A control unit 19 including a microprocessor and infrared links switches the triac 17 in accordance with the operation of remote switches 21 and may control dimming. The arrangement is such that the connection between the switches 21 and the control unit 19 are DC and low voltage and the connections between the control unit 19 and the triacs 17 require only a very low current. Both these factors enable simple and cheap wiring to be achieved. The system may provide a flashing alarm responsive to fire or an intruder. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electrical supply systems This invention relates to improvements in or relating to electrical supply systems, and to elements thereof.

In known electrical supply systems, such as supplies for lighting, air conditioning etc., devices connected to the supplies are switched by directly switching the supply. This means that all the switching elements and their associated wiring have to be capable of handling the full current and voltage of the supply. Further all wiring has to be installed in a manner which meets stringent safety requirements.

For example wires have to be passed through conduits and cannot be merely embedded in the walls of a building. The result is such systems are expensive both to manufacture and install.

It is an object of the present invention to provide a cheaper and more versatile electrical supply system.

From one aspect the invention consists in an electrical supply system comprising an electrical supply having a series of taping points spaced along at least part of its length for connecting an electrically operable device to the supply, each tapping point including or being connectable to a switchable element for connecting and disconnecting the device to the supply and a remote instruction unit for each device for switching the element of its respective tapping point.

In a preferred embodiment the system further comprises a control unit for generating a switching signal for switching the element in response to operation of an instruction unit. In this case the connections between the instruction units and the control unit are preferably DC and/or low voltage connections and the switching signal is a current of less than 100 m.A.

Conveniently the supply is an AC supply and the control unit may monitorthe supply to generate the switching signal when the supply is at zero volts.

(This latter arrangement is not particularly desirable for inductive loads). The control unit may scan the instruction unit cyclically and preferably does so at least once every half cycle to produce switching signals, if instructed, every half cycle. In this case, the switchable element may be a triac or the like and the control unit may be arranged, in respect of at least one instruction unit, to delay the generation of the switching signal on each half cycle to achieve a reduced power supply to the respective tapping point.

The supply may be at least in part constituted by a series of trunking elements containing busbars and including tapping points, in which case, the trunking elements may be electrically connectable end-to-end by snap-fit plugs.

In a preferred arrangement the switchable elements and/or associated fuses are disposed at or adjacent their respective tapping points.

The trunking elements may constitute a support for the devices, when the devices are, for example, light fittings.

From a second aspect the invention consists in a trunking element containing a busbar or other electrical supply extending along its length, at least one tapping point for connecting an electrically operable device to the supply, the tapping point including a switchable element for connecting and disconnecting the device to the supply and means for connecting the element to a remote instruction unit.

In any of the above cases the instruction units may be push-button switches, photoelectric cells, thermistors, fire alarms or any other switch or transducer. More than one instruction unit may be provided for any device, in which case, they may be connected in parallel.

The control unit may be arranged to introduce a time delay before activating a device, or it may limit the period of operation of the device. It may also be arranged to vary the magnitude of the current supplied to a device in accordance with the period of operation of the switching element, e.g. it may provide an instruction.

The system or the trunking element may be provided with tapping points for different types of devices, e.g. power operated devices, such as ventilatorfans, or lights.

It will be appreciated that all connections between the control and the instruction units need only handle low level voltages and they can therefore be extremely cheap wire, such as telephone wire.

The invention may be performed in various ways, a specific embodiment of which will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa schematic circuit diagram of part of an electrical supply system; Figure 2 is a view of part of a trunking system incorporating the supply system of Figure 1; Figure 3 is a cross section of a trunking element of Figure 2; and Figure 4 is a schematic circuit diagram showing the system of Figure 1 in more detail.

A part of an electrical supply, generally indicated at 10, is shown in Figure 1. The supply 10 comprises a three phase AC supply busbar 11, and a lighting tapping point 12. The tapping point has a socket 13 into which a light 14 can be plugged. The socket 13 is connected to the busbar 11 by cables 15 and 15a.

The cable 15a has a fuse 16 and a triac 17 connected therein in series.

The gate 18 of the triac 17 is connected to a control unit 19 by a control signal lead 20. A series of switches 21 are connected to the inputs of the control unit 19. There is a switch 21 for each tapping point 12 in the supply and a corresponding lead 20.

The control unit 19 scans the switches 21 and whenever it senses operation of a switch 21 it sends a signal to the corresponding triac to change its state thus switching the light 14 on or off.

The switching of the triac may be controlled by a transistor (not shown) at the output of the control unit. The transistor is connected via a bridge to the AC electrical supply such that it only allows an output signal from the unit to be supplied to the triac when the supply is at zero volts. This arrangement greatly increases the life of the bulb of the light 14.

In the preferred embodiment the busbar 11 and the leads 20 are contained in electrical trunking 22, which also carried the socket 13, fuse 16 and triac 17.

The trunking may be formed of a series of prewired elements, which can be plugged together end-toend. The trunking may also be constituted by a support for the light 14 by means of brackets 23.

Figure 4 shows the electrical arrangement of the supply system 10 in somewhat greater detail, although it will be appreciated that the diagram is still schematic. As can be seen cables 15 and 15A connectthetriac 17 and lights 14betweenthe live wire Land the neutral wire N of the three phase AC supply 11. Also connected between these wires is a transformer 24 which supplies power to the input circuitry 25 of the control unit generally indicated at 19. The major function of the circuitry 25 is to ensure the power supplied to the control unit's microprocessor 26, and to the gates 18 of the triac 14, is exactly in phase with the supply on lines Land N.

For the purposes of simplicity only two switches 21 and two triacs 17 have been indicated, but is will be appreciated that the interconnections described can apply throughout the system. One of the switches 21A is associated with a triac 17A whilst the other 21B is associated with triac 17B. The arrangment described belowforswitch 21Aandtriac 17Ais a more general one, whilst that for 21 B and 17B illustrates the dimming function.

Taking the triac 1 7A arrangement first, the operation is as follows: The microprocessor 26 scans the switches 21 cyclically four or five times for each half cycle of the supply. When it detects the closure of switch 21A it generates an output on pin 27 which causes a current to flow through an infrared emitting diode 28 of an optocoupler 29. The infrared emission caused is detected by transistor 30, which then conducts and causes the triac 17A to be switched on. As is well known the triac will then continue to conduct until the supply voltage on lines Land N falls to zero at the end of the half cycle. The microprocessor then generates a further switching signal on pin 27 and continues to do so every half cycle until it detected the subsequent operation of switch 21A.

It will be seen that although the line 20 is connected across the mains the switching voltage required by the triac gate is very small and hence the current is normally of the order of only 30 m.A. This means that whilst the line 20 has to be mains insulated only a very thin light wire is needed and hence it is easy to feed many of these wires through the lower half of the trunking 22.

Switch 21B and triac 17B operate in much the same manner except that the microprocessor is arranged to delay the generation of the switching signal to the respective opto-coupler 31 by a period, which is preferably dictated by the length of time for which the switch 21 B is depressed. The later in the half cycle that the signal is generated the less the power fed to the line 14.

It is generally preferred that the triac 17 be located at the tapping point 12, as described above, but many of the advantages of the invention can still be obtained if the triacs are grouped together near the control unit and this may be preferable in certain circumstances.

It will be appreciated that the switches may be constituted by any devices which either manually or automatically change their state. For example they may be constituted by a fire or intruder alarm, in which case the control unit may be arranged to flash the lights. As has been mentioned the control unit may provide a dimming facility, in addition limited time and delayed operation of the lights or other devices may be achieved.

The system can be used to control any electrically operable device.

As the instruction units are operating a microprocessor only very small voltages are required and therefore very thin wire can be used for all the control connections. Thus the wiring to switches is extremely cheap, and there is no significant danger of electrocution, electric fires etc. Thus switches can be easily and cheaply installed, and cheap pushbutton switches can be used. Further the signals genrated by such switches are suitable for direct input into any controlling or monitoring computer.

They can also be sent via telephone links allowing remote operation of lights etc. in a building.

Claims

1. An electrical supply system comprising an electrical supply having a series of tapping points spaced along at least part of its length for connecting the electrically operable device to the supply, each tapping point including or being connectable to a switchable element for connecting and disconnecting the device to the supply and a remote instruction unit for each device for switching the element of its respective tapping point.

2. A system as claimed in Claim 1 wherein the element is constituted by a solid state device.

3. A system as claimed in Claim 1 or Claim 2 further comprising a control unit for generating a switching signal for switching the element in response to the operation of an instruction unit.

4. A system as claimed in Claim 3 wherein all of the connections between the instruction units and the control unit are DC and/or low voltage connections.

5. A system as claimed in Claim 3 or Claim 4 wherein the switching signal is a current of less than 100 m.A.

6. A system as claimed in any one of Claims 3 to 5 wherein the supply is an AC supply and the control unit monitors the supply to generate the switching signals when the supply is at zero volts.

7. A system as claimed in any one of the preceding claims wherein the control unit scans the instruction unit cyclically.

8. A system as claimed in Claim 7 wherein the supply is an AC supply and the control unit scans the instruction units at least once every half cycle to produce switching signals, if instructed, every half cycle.

9. A system as claimed in any one of the preceding claims wherein the supply is an AC supply wherein the switchable element is of the type which once switched on continues to conduct until the voltage across it drops below a predetermined level and wherein the control unit delays the switching signal, generated in response to the operation of at least one instruction unit, each half cycle to achieve a reduced power supply to the respective tapping point.

10. A system as claimed in any one of the preceding claims, wherein the supply is at least in part constituted by the series of trunking elements containing busbars and including the tapping points.

11. A system as claimed in Claim 10 wherein the trunking elements may be electrically connectable end-to-end by snap-fit plugs.

12. A system as claimed in any one of the preceding claims, wherein the switchable element and/or associated fuses are displayed at or adjacent their respective tapping points.

13. A system as claimed in any one of the Claims 10 to 12 wherein the trunking elements constitute a support for at least one of the devices.

14. A system as claimed in any one of the preceding claims wherein the instruction units are push-button switches, photoelectric cells, thermistors, fire-alarms or any other switch or transducer.

15. A system as claimed in Claim 13 wherein more than one instruction unit is provided for at least one tapping point and wherein those instruction units are connected in parallel.

16. A system as claimed in Claim 3 wherein the control unit is arranged to introduce a time delay before activating a device, to limit the period of operation of a device, or to vary or reduce the magnitude of the current supply to a device in accordance with the period of operation of the instruction unit.

17. Atrunking element containing a busbaror other electrical supply extending along its length, at least one tapping point for connecting an electrically operable device to the supply, the tapping point including a switchable element for connecting and disconnecting the device to the supply and means for connecting the element to a remote instruction unit.

18. Atrunking element containing an electrical supply substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

19. An electrical supply system substantially as hereinbefore described with reference to the accompanying drawing.