|WO/1996/030989||CIRCUIT INTERRUPTER INCLUDING AN ELECTRIC ARC MONITORING CIRCUIT|
|JP2000274142||SAFETY DEVICE FOR POWER WINDOW|
A significant number of fires that originate in electrical systems are caused by faulty contacts at connection points between conductors in wires and e. g. connection boxes, plugs, switches and other electrical equipment, hereinafter termed an apparatus. A contact fault may cause overheating to occur, which affects both the electroconductive material with regard to thermal expansion and corrosion, and the insulation material with regard to deformation and brittleness.
Typically, overheating will after a period of use lead to loose contact connections, where the conditions are favourable to the formation of arcs between wire components and the apparatus. The loose connections may be due to e. g. incorrect installation, vibrations or overloading.
When using insulation material of the polyvinyl chloride type, the insulation material may upon heating release gases that have a corrosive effect on the metal conductors.
Periodic checking of electrical connection points is highly labour intensive and costly as a result of concealed and built-in wiring. Such checking is therefore not very practical in conventional houses and office buildings.
Today's requirements for protection of wiring circuits through the use of fuses have little effect when it comes to protecting against arcing, as an arc can occur without any significant increase in amperage through the circuit. The increase in amperage that is required to trip a fuse may occur e. g. in the case of an arc between conductors of different polarity. In the case of an arc between a conductor and earth, any earth fault switch will be tripped first.
Monitoring of electrical system noise has been proposed as a means of monitoring electrical systems, among other things with regard to arcing. The formation of an arc in an electric circuit is known to alter the noise conditions to a certain extent. It may however still be difficult to reliably separate the arcing noise from other noise, in as much as it may be a case of relatively weak arcs created in large electrical systems.
The object of the invention is to remedy the drawbacks of prior art.
The object is achieved in accordance with the invention by the characteristics stated in the undermentioned description and in the appended claims.
Electrical connection points, e. g. in the connection box of a motor or behind a wall contact, are monitored with regard to light intensity and/or light frequency. Upon flashover or arcing, light is emitted in a wide spectrum that may be detected by a light sensitive sensor, preferably in the form of a light sensitive diode. A warning lamp and/or an acoustic warning may be activated by means of an electrical circuit connected to the sensor. The light sensor may advantageously be designed to operate outside of the visible light spectrum, e. g. in the ultraviolet frequency range, thereby to avoid being influenced by visible light.
The electrical control/warning circuit may be equipped with a memory function designed to maintain the warning, even after the arc has been broken.
In a preferred embodiment, the warning device is constructed as a compact device adapted and designed to allow retrofitting into e. g. a wall socket. In addition to a power supply, a light sensitive sensor and a control circuit, the device also comprises outlets for delivering a warning by means of a lamp and/or a loudspeaker.
Preferably, the power supply receives voltage from the connection points that are to be monitored or from another, preferably nearby. supply point. If a light sensitive diode is used, the resistance through the diode will change when arcing occurs. The control circuit is affected by the change in resistance, and delivers a voltage at one or more warning outlets that may optionally be connected to the warning lamp and/or loudspeaker via an amplifier. The sound and/or light signal may be heard/seen by persons who are in the area, and
any required repair of the contact point where the arcing occurred, may be carried out.
The device may if so desired be provided with a relay outlet designed to disconnect the power supply from the subsequent apparatus.
In an alternative embodiment, the device is also provided with a temperature sensor. The temperature sensor is designed to sense an increase in temperature in the contact point of the apparatus.
The following describes a non-limiting example of a preferred embodiment illustrated in the accompanying drawings, in which: Figure 1 shows a wiring diagram for a warning device according to the invention.
Figure 2 shows the wiring diagram of Figure 1, but with the addition of a temperature sensor.
In the drawings, reference number 1 denotes a warning device for arc monitoring in electrical contact points, comprising a power supply 2 that may be provided with a back-up capacitor (not shown) and a required noise filter, a light-sensitive diode 4 and a control part 6. The power supply 2 supplies voltage from the electrical connection points l0 and 12, which are subject to monitoring, via wires 14 and 16. The power supply 2 supplies the diode 4 and the control part 6 with power via wires 18,20 and 22, respectively. The diode 4
is connected to earth at its connection point 24 to the control part 6, through a resistance 26.
A signal reset switch 28 is connected to the wire 18 and the control part 6, respectively, via a wire 30.
When arcing occurs, the resistance of the light sensitive diode 4 changes. The control part 6 processes the signal from the diode 4 and delivers a voltage at one or more outlets, e. g. via a wire 32 to a warning lamp 40, via a wire 34 to an amplifier 42, and via a wire 36 to a relay 44. The amplifier 42 is supplied with voltage through the wire 18, and is designed to supply a loudspeaker 48 with voltage via a wire 50.
The relay 42 is designed to break the supply of voltage through wires 52,54, which supply the subsequent apparatus (not shown).
All components 2,6,26,42,44,48 and 56 are connected to earth.
In an alternative embodiment, see Fig. 2, the warning device is equipped with a temperature sensor 56 supplied with voltage through the wire 18 and a wire 58, and the temperature sensor 56 is connected to the control part 6 via a wire 60.
Upon reaching a temperature higher than the set danger level, the control part 6 will, in a similar manner to that described above, deliver output voltages.
A device in accordance with the description is well suited for retrofitting in a number of traditional domestic and industrial appliances and contact points. Implementation of the method according to the invention may therefore prevent a large number of fires caused by faulty electrical systems.
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