ELECTRONIC CONTROL AND PROTECTION DEVICE

Abstract: Facade heating of a building is provided by mounting a polymeric self-regulating heater (12) within the framework surrounding the glass panels. An electronic earth leakage current breaker (2) is used with the heater (12) and can be subjected to potentially-damaging high ambient temperatures under normal load conditions. A temperature sensor (6) is arranged to sense ambient temperature and to activate the ELCB (2) at a predetermined temperature so as to switch off the current therethrough and through the heater (12).

Description: ELECTRONIC CONTROL AND PROTECTION DEVICE This invention relates to an electronic control and protection device, and in particular to such a device for use in association with a heating element. Earth leakage current breakers (ELCBs) are known for plugging in between a source of electrical power and electric equipment to ensure the safety of an operator of the equipment under fault or other conditions that could otherwise give rise to flow of a dangerously high earth current, of greater than about 10mA, through the operator. Traditionally, ELCBs are heavy, rugged pieces of equipment containing a lot of metal that can generally withstand high ambient temperatures under normal load conditions. GB Patent No. 1 208 208 discloses an earth-leakage transformer having a positive temperature coefficient resistor that responds to the heat generated in the coils of the trans¬ former under conditions of sustained overload to operate a trip coil. Known electronic ELCBs however are limited to operating under normal conditions in maximum ambient tem¬ peratures of about 45°C when power is being supplied through them to the associated equipment. However, applications exist in which the temperature can reach 60°C to 70°C under normal load conditions either due to the electrical power supplied or due to heating from another source e.g. the sun. For example a self-regulating electric heater, that is to say one having a positive temperature coefficient of resistance, mounted inside the metal facade surrounding a window can reach 60°C in the winter. In these circumstan¬ ces, it may not be convenient to locate the electronic ELCB physically near the heater since it would have to be switched off. On the other hand, the traditional ELCBs are electromechanical devices and consequently too bulky for applications such as facade heating. Elongate heating elements, including those of the self- regulating type, are not always installed by electrically skilled personnel, so that extra safety must be ensured in the products as sold by the manufacturer. One object of the present invention is to provide an electronic control and protection device having improved safety during installation and during operation. In accordance with one aspect of the present invention, there is provided an electronic control and protection device comprising electronic means arranged to interrupt the flow of electrical power in response to an earth fault leakage current above a predetermined value, and temperature sensing means arranged to activate the electronic means in response to an ambient temperature of the electronic interruption means above a predetermined value, thereby to produce said interruption of electrical power. Thus, the electronic ELCB is protected even during nor¬ mal, i.e. non-overload, operating conditions, against excessive ambient temperatures. The power interruption means, an electronic ELCB employing semiconductor chips, needs to be protected against an ambient temperature is excess of about 45°C when under load. By appropriate selection of components, in particular the semiconductor chips, the critical ambient temperature may in fact be greater than 45°C. Accordingly, the tem¬ perature sensor is arranged to switch the ELCB off when such predetermined temperature is exceeded. Consequently, the electrical equipment controlled by the ELCB is also switched off. The electronic ELCB is no longer under load conditions and is thus able to withstand exposure to a much higher ambient temperature, say up to 80°C or even 100°C. The temperature sensing means may alternatively be set to activate the ELCB at a lower predetermined temperature, say in a range between about 20°C and 45°C. Such a lower temperature may be the chosen cut-off temperature of a body associated with the control device. In particular, the ELCB may be interposed in an electric circuit between a power supply cable and a heater cable, and the control and protec¬ tion device may be made responsive to a predetermined tem¬ perature of the apparatus heated by the heater. The predetermined activating temperature may be variably selected either manually at the device itself or remotely. Remote control may be connected via a computer, so that, for example, the amount of heating provided at dif¬ ferent parts of a building can be variably controlled as required. Adavantageously the heating element is an elongate heating cable exhibiting a positive temperature coefficient (PTC) of resistivity, and is thus self-regulating. Such a heater is available from Rayσhem under the trade names CHEMELEX, AUTOTRACE and INTERGARD. The cable, power or heater, connected to the control and protection device is preferably connected thereto within an enclosure for reasons of safety, and also to protect the device and its connections. The materials used are pre¬ ferably substantially unaffected by any adverse environment to which they may be exposed, such as moisture condensation, salts and other ionic contaminants such as are found in industrial and coastal locations for example. Further installation and operational safety and con¬ venience are provided by arranging for any cable, power or heater, extending from the control and protection device to have its free end terminated. That is to say, the free end of the cable will be completely sealed off, such as the ter¬ mination of a PTC heater cable, or have a connector or plug fitted thereto. In one application of the present invention, a pre- terminated power supply cable is connected to the control and protection device within a compact enclosure of cross- section 15 x 15mm and length 120mm. A WINTERGARD PTC heater cable from Raychem is also connected to the device within the enclosure and extends therefrom through aluminium extruded profiles of a facade heating construction. Alter¬ natively, the heater cable may be located remote from the enclosure and connected to the device therein by means of a further power cable lead. A temperature sensor, for example a thermostat, may be arranged to sense the temperature of the facade and to activate the electronic ELCB when a prede¬ termined surface temperature is reached. This will switch off flow of power through the device and thus through the heater. Some embodiments of electronic control and protection devices, each in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows schematically a basic version of the device and indicates some preferred optional features; and Figure 2 shows schematically a more complex version of the device. Referring to Figure 1, an electronic earth leakage current breaker 2 that is capable of withstanding a maximum temperature of 45°C under load conditions, is mounted inside an enclosure 4. A temperature sensor 6 is mounted on the outside of the enclosure 5 and is electrically connected to the ELCB 2 via a switch 8. A power cable 10 enters the enclosure 4 and is connected to the switch 8. A self- regulating heater cable 12 has its power supply cable 14 extending into the enclosure 4 and connected to the ELCB 2 and to the switch 8 by a further switch 16. In the event of an electrical fault that gives rise to a current flow through the ELCB 2 in excess of its trip value of 10mA, the ELCB operates to open the switch 16 thus cutting off the power supply to the heater 12. In the event of the temperature sensor 6 detecting an ambient temperature in excess of its trip value of 45°C, it is arranged to operate the switch 8 thus cutting off the power supply to the heater 12 and also to the ELCB 2 so that the latter component is not under load above its maximum operating temperature. As an optional feature, the temperature sensor 6 may have a control arrangement 18 associated therewith in order that its critical ambient or trip temperature may be set at a predetermined value anywhere within the range 20°C to 45°C. The control arrangement 18 may be mounted alongside the sensor 6 on the enclosure 4 and operated manually, or it may be located remote therefrom as shown at 20, with a cable connection thereto, and operated manually or preferably by a computer. The electronic control and protection device of Figure 2 includes all the components of Figure 1, which for con¬ venience have been given the same reference numerals, and some additional components. Reffering to Figure 2, a switch 22 is connected in parallel with the switch 16 so as to be operated simulta¬ neously therewith by the ELCB 2. An indicator lamp 24 in series with the switch 22 is mounted on the outside of the enclosure 4, and a cable 26 extends from the lamp 24 to remote equipment which may be an indicating and/or control equipment. When the ELCB 2 opens the switch 16, as described with reference to Figure 1, the switch 22 is also opened and the normally on lamp 24 is extinguished, and this is detected and indicated in an appropriate manner by remote alarm indicating equipment. The existence of an electrical fault is thus indicated locally on the enclosure 4 of the device itself and also remotely. A further indicator lamp 30 is mounted on the outside of the enclosure 4 and electrically connected to the switch 8 in order to indicate locally whether or not electrical power is supplied to the ELCB 2 and heater 12. A cable 32 also conveys this information to remote indicating equipment. A cable 34 extends also from the temperature sensor 6 to remote equipment for indicating the actual ambient tem¬ perature, and/or the fact that the critical temperature has been reached or exceeded. The various pieces of remote equipment referred to above may be separate, or may be combined together, giving information on the status of the various components of the protection and control device, indicating a fault or alarm condition, or exercising a control function as appropriate. It is to be understood that a protection and control device in accordance with the invention may include selected ones only of the components and features described herein. The device of the present invention may advantageously be used in facade heating of a building. Thus, the electro¬ nic control and protection device may be made small enough to be located within the framework, usually of good ther¬ mally conductive material such as metal, surrounding a win¬ dow or a door of a building that is subject to large heat loss, for example through glass panels. The heating, to counteract the cold effect felt by a person in the vicinity of a large glass panel of a heated building, may con¬ veniently be achieved by one or more self-regulating heaters, for example polymeric PTC (positive temperature coefficient) heaters as sold by Raychem under the tradenames CHEMELEX and AUTOTRACE, also mounted within the framework. In such an arrangement, when the ambient temperature of the electronic earth leakage current breaker exceeds a predeter¬ mined value the temperature sensor will arrange for current therethrough to be interrupted and so maintain the integrity of the electronic ELCB.

Claims: CLAIMS 1. An electronic control and protection device comprising electronic means arranged to interrupt the flow of electri¬ cal power in response to an earth fault leakage current above a predetermined value, and temperature sensing means arranged to activate the electronic means in response to an ambient temperature of the electronic interruption means above a predetermined value, thereby to produce said interruption of electrical power. 2. A device according to claim 1, wherein the value of the predetermined temperature can be varied. 3. A device according to claim 1 or claim 2, mounted within an enclosure, having one end of a power supply cable connected to the device within the enclosure, the cable extending out of the enclosure and being terminated at its other end, and having a further electric cable connected at one end to the device within the enclosure, which further cable extends out of the enclosure and is terminated at its other end. 4. A device according to claim 3, wherein said further electric cable is a heater cable, preferably a self- regulating heater cable. 5. Electrical apparatus comprising a device according to any preceding claim that electrically interconnects a power supply cable and an electric heating element, wherein the temperature sensing means is arranged to be responsive to the temperature of apparatus heated by the heating element. 6. Apparatus according to claim 5, wherein the heating ele¬ ment comprises a polymeric heater cable exhibiting a posi¬ tive temperature coefficient of resistance. 7. A device or apparatus according to any preceding claim, being arranged to send a signal to remote equipment indi- eating whether the electronic means is activated or not, and/or whether the predetermined value of the ambient tem¬ perature has been exceeded or not. 8. A facade of a building comprising a thermally-conductive framework within which is mounted a device in accordance with any one of claims 1 to 4. 9. A method of heating a body wherein an electric heating element is arranged to provide heat to the body, electronic means is arranged to interrupt the flow of electrical power to the heating element in response to detection of an earth fault leakage current above a predetermined value, and wherein temperature sensing means is arranged to activate the electronic interruption means in response to an ambient temperature of the electronic means above a predetermined value, thereby to produce said interruption of electrical power. 10. A method according to claim 9, wherein the heating ele¬ ment is arranged to heat the facade of a building, and wherein the electronic means is mounted within the framework of the facade. 11. A method of heating a body using a device or apparatus according to any one of claims 1 to 7.

Inventors: CLAASSEN CLAUS, STANZEL ERWIN, CLAASSEN, CLAUS, STANZEL, ERWIN
Applicants: RAYCHEM GMBH, RAYCHEM LTD, RAYCHEM LIMITED
Application year: 1989
Main classification: H02H3
IPC codes: H02H3, H02H5, H02H7