WO2009128102A1

WO2009128102A1 - Safety electrical socket and use of said socket in electric systems with automatic load control

Info

Publication number: WO2009128102A1
Application number: PCT/IT2008/000260
Authority: WO
Inventors: Giovanni Nocera; Martino Bonacossa
Original assignee: Giovanni Nocera; Martino Bonacossa
Priority date: 2008-04-17
Filing date: 2008-04-17
Publication date: 2009-10-22

Abstract

A safety electrical socket comprises a low-voltage, electronic circuit (1,2, 3) for the recognition of the type of electrical appliance connected to the socket, a microrelay (9) allowing the switching of the socket terminals (8) between said low-voltage circuit and the mains voltage (7), and a microcontroller (6) capable of picking up the signals coming from said circuit for the recognition of the electrical appliance. The microcontroller (6) activates said microrelay for connecting said socket to the mains voltage (7) only when the electrical appliance is recognised as an electrical appliance.

Description

SAFETY ELECTRICAL SOCKET AND USE OF SAID SOCKET IN ELECTRIC SYSTEMS WITH AUTOMATIC LOAD CONTROL

The present invention concerns a safety electrical socket, of the type used for the introduction of connecting plugs of supply conductors of electrical appliances. The present invention also concerns the use of said socket in electrical systems wherein an automatic control and a selection of the electric loads existing in the various sockets is performed. Safety electrical sockets of this type are already widely known and some examples are given in EP-O .746.058, DE-I .218.035, FR-2.619.996. In all these known electrical sockets, safety is provided by a shutter which closes a pair of holes for the introduction of a connecting plug and which may be moved, to provide access for the plug, only if both the plug jacks press simultaneously on the shutter. As can be understood, this arrangement is such that the accidental introduction of a foreign body into one only of the holes - with the resulting risk of electrocution - is prevented. However, these known electrical sockets provide a very relative safety, due to the fact that the safety system is based on a mechanism wherein the components are generally relatively fragile and easily prone to wear following frequent operation. Moreover, these safety systems offer no guarantee in case of simultaneous introduction of a pair of foreign bodies, as well as in case of introduction of plugs whereto cables are connected which are even only partially exposed in the area in contact with the user.

A first object of the present invention is hence that of providing an electrical socket which overcomes the above- described drawbacks of known-art sockets and hence offers conditions of high safety with regard to the accidental or voluntary introduction of foreign conductive bodies into one or both the socket holes . Moreover, known-art sockets offer of course no safety in case a plug is introduced therein, whereto cables or, more generally, electrical appliances are connected which are not correctly insulated. Safety in these cases is currently guaranteed only at central system level, by the adoption of the well-known general short-circuit, magnetothermic and differential switches; the first one being capable of interrupting the supply of current when a short-circuit occurs, the second instead when the current absorbed exceeds by a preset value the maximum admissible one for the particular supply contract, and the third one residual current device - known also under its original commercial name "salvavita" ("life-saving") - when instead a significant difference is detected between incoming and outgoing current flows, a sign of the presence of electrical leakage in the circuit.

The drawbacks inherent in this conventional plant solution stem precisely from the fact that control is performed centrally, and are well-known. Firstly, when current detachment following a fault has not occurred at the same time as the introduction of a plug into a socket, the user has no information on where the fault has actually occurred and can hence proceed only by trial and error in his search. Since current breakdown concerns in any case the entire circuit, the user finds himself also in the unpleasant situation of not being able to utilise in any way the electric service, or at least in part if the system is partitioned, until the fault has been identified and fixed. This can of course give rise to situations possibly of severe distress when the fault occurs at night time or in the absence of people who have a minimum of familiarity with the electric system, such as for example a number of elderly people and children.

A second object of the present invention is hence that of providing an electrical socket which guarantees conditions of great safety also with respect to electrocution or to other adverse conditions - such as for example the interruption of the operation of the entire circuit - which may occur when apparatuses with poor or faulty insulation are connected to the socket, which are potentially capable of determining short- circuits or current leaks.

These objects are achieved, according to the present invention, through a safety electrical socket having the features mentioned in claim 1, wherefrom it can be detected that, according to the invention, socket safety is accomplished entirely electronically and hence without mechanical moving parts, through a low-voltage, electronic control circuit with integrated microcontroller which performs a recognition of the type of appliance connected to the socket before authorising power supply. Additional features of the socket according to the present invention and of its use in electric systems are defined in the dependent claims .

Further features and advantages of the safety socket according to the present invention will in any case be evident from the following detailed description of a preferred embodiment of the same or, more precisely, of the electronic circuit which governs and controls operation thereof, said circuit being illustrated in the accompanying drawings, wherein: fig. 1 shows a diagram of the principle of operation of that part of the electronic circuit governing the recognition of the type of load applied to the safety socket; fig. 2 shows a diagram of the recognition and supply circuit according to the invention, during non-supply of current ; fig. 3 shows the same diagram of fig. 2 during current supply; fig. 4 shows the same diagram of fig. 2, completed with a circuit for protection from short-circuits; and fig. 5 shows an additional circuit for differential and magnetothermic protection.

The main feature of the safety electrical socket according to the present invention is that it comprises an intelligent electronic control, i.e. provided with an integrated processing unit, or microcontroller, which, before giving consent to current supply, performs periodic checks of the electrical features of the appliance possibly connected to the socket. Depending on the results of these checks, current supply to the appliance is authorised or denied. Periodical checks of the electrical features of appliances are continued also after the current supply has been authorised and, depending on the results of these further checks, the supply is continued or interrupted. Going into greater detail now, the electronic control circuit of the electrical socket according to the present invention comprises firstly a function capable of recognising which load is applied to the safety socket, in particular if it is a load corresponding to an electrical appliance or instead a load corresponding to accidental human contact .

This circuit uses a particular electronic component called photocoupler consisting essentially of a photodiode and of a phototriac coupled together. A device of this kind is easily available on the market: it is for example the component bearing code MOC3020.

Fig. 1 shows the principle diagram of a recognition circuit comprising a photocoupler 1,2 which acts as connecting element between a primary circuit containing photodiode 1 (left part of the circuit of fig. 1) and a secondary circuit containing phototriac 2 (right part of the circuit of fig. 1) . The primary circuit is supplied with direct current by a power supply 3 and when switch 5 is in its closed position, the circulating current maintains the photodiode polarised. In this condition, phototriac 2 keeps the secondary circuit closed, so that if alternating current is made to circulate therein by a generator 7, an electrical appliance connected in series - in the example circuit of fig. 1, a light bulb 4 - will become active. In a preferred embodiment, in order to polarise photodiode 1, an inverted current of 1.6 V is applied to the ends thereof to circulate a current of 35 tnA. Employing a voltage of about 12 V cc, generated by supply 3, it is necessary to arrange in series a resistance R2, for example a 220 Ohm resistance, such as to guarantee the above-said polarisation current .

Switch 5, which is shown in the primary circuit, diagrammatically represents the type of load applied to the socket : as a matter of fact the switch can be considered closed where at its terminals an appliance is connected, which as a matter of fact has a very low internal resistance, while it may be considered open where said terminals are put in short-circuit through the human body, which on the contrary has a very high internal resistance. The low voltage used in the primary circuit causes a minimal current to run through the human body, hence insufficient to polarise photodiode 1.

Having thereby clarified the principle of operation of the recognition circuit described above, the functionality of the recognition and supply circuit actually used in the socket of the present invention is immediately clear, which is schematically illustrated in figures 2 and 3, in load- recognition and supply phase, respectively. The already described elements may be recognised here in connection with the principle diagram of fig. 1, i.e. photocoupler 1,2, low-voltage supply 3 and resistance R2. In this case, the secondary circuit is connected to a microcontroller 6, for the function better described in the following. Various types of microcontroller devices of this type are widely available on the market; an example of microcontroller suitable for this purpose is marked by code PIC16F676. On .the left hand side of drawings 2 and 3 an alternating- current source of supply 7 is also shown - for example mains voltage at 220 V, 50 Hz - intended for the supply of the electrical appliance which will be connected to the terminals 8 of the safety socket. A microrelay switch 9 is capable of connecting terminals 8 to the primary recognition circuit or, alternatively, to supply source 7, under the control of microcontroller 6, in the way described in the following.

In rest conditions (shown in fig. 2), microrelay 9 connects terminals 8 to the primary recognition circuit 1,2, 3, R2 : no current circulates because no load is applied to terminals 8 (situation corresponding to that of open switch 5 in the principle diagram of fig. 1) .

In work conditions, and hence when an actual load is applied to terminals 8, for example the load of an appliance, the primary circuit is closed by the internal circuits of said appliance and the low-voltage current generated by supply 3 polarises photodiode 1, hence allowing the flow of current into the secondary circuit through phototriac 2. This current flow is recognised by microcontroller 6, which controls the snap of microrelay 9 into the work position (position shown in fig. 3) ; network voltage 7 is then applied to terminals 8, which duly supply the appliance.

When terminals 8 are not connected to an electrical appliance, but are instead put in short-circuit by a part of the human body - for example a finger, either directly or through an electrically-conducive element - the current which is thereby circulated through the human body is of such modest power - due to the low voltage of the current generated by supply 3 and by the high resistance of the human body - to be fully insufficient for polarising photodiode 1. Phototriac 2 hence allows no current circulation in the secondary circuit and microcontroller 6 sends no activation control to microrelay 9, which consequently remains in its rest position. In the end, on terminals 8 no voltage current can circulate and only the low- voltage (12 V cc ) detection current remains, which is entirely safe for the human body.

From the preceding description it is immediately clear that the above -said safety condition, wherein the mains voltage is not supplied to the socket, occurs also when the electrical appliance connected to socket 2 has an internal switch in an open position. As a matter of fact, in that case the internal circuit of the appliance has an infinite resistance and the socket consequently delivers no current. Therefore, unlike conventional sockets, the power cable of the electrical appliance does not remain live when the appliance is not switched on.

The recognition and supply circuit shown in figs. 2 and 3 is furthermore advantageously integrated by a short-circuit detection circuit, for example such as the one schematised in fig. 4, which allows to detect the presence of a short-circuit in the appliance before supply from mains voltage is authorised. This circuit has a fully identical structure to the recognition circuit described above, except for the fact that entry to the circuit goes through a voltage-limiting diode 10, which allows voltage to pass above a defined nominal value. A device of this type is easily available on the market: it is, for example, the component marked by codes BZV60-C9V1 or BZV55- C9V1. The above-said nominal value of diode 10 is calculated so as to be in any case higher than the voltage which may be generated at the terminals of a generic electrical appliance in normal conditions, i.e. not in the presence of short-circuit.

In this case too any current signal passing through limiting device 10 is capable of determining the polarisation of photodiode Ic and hence the flow of current through phototriac 2c, supplying microcontroller 6 with a signal which is interpreted as the presence of a short-circuit. In the presence of this signal, microcontroller 6 does not activate microrelay 9, preferably signalling the presence of the short-circuit through a LED and/or a buzzer mounted on the socket.

This same preventive action controlling short-circuit presence occurs of course also when the plug of the electrical appliance is inserted in the socket but the appliance has its own internal switch in the open position. Assuming for example a switched-off iron, i.e. when the appliance is not normally supervised; an action on the power cable determining the deliberate or accidental breakage and hence the short-circuit thereof, as may happen relatively easily in play or distraction situations involving children or elderly people - would cause - unlike what occurs at the moment - no consequences to the person nor to the system. As a matter of fact, the microcontroller will thereby immediately signal the presence of a short-circuit, such condition being signalled by the activation of the LED and/or of a buzzer, despite continuing to maintain the socket fully disconnected from the mains voltage.

Finally, the electronic control circuit of the socket according to the present invention may also advantageously comprise further circuits of magnetothermic and differential protection, such as those outlined in fig. 5. These circuits allow to perform at the level of each individual socket the controls of absorbed load intensity and power leakage which are currently performed only at central system level . Similarly to what has been described in connection with the pre-supply short- circuit detection circuit, in this case too the check outcome is interpreted by the microcontroller as calling for immediate power deactivation from the mains supply and for fault signalling by activating a LED and/or a buzzer, with the extraordinary advantage of causing no inconvenience to the user other than the simple deactivation of the individual socket where the fault has occurred. The light signal activated by the magnetothermic protection can possibly be the same short-circuit signal described above and the relevant circuit can be adjusted to the maximum admissible load for the socket, thereby allowing to avoid those socket overloads which can easily occur when employing the common multiple sockets available on the market, when the user is not sufficiently careful . For the light signal of the differential protection, it is instead by all means useful to have an independent, differently-coloured LED and/or a buzzer. As a matter of fact, the maintenance operations to be performed by the user in this case are of a different kind from the previous ones since, in general, the fault is less obvious to detect.

Fig. 5 shows schematically the magnetothermic and differential circuits described above which comprise current transformers 11 and 12, i.e. coils, capable of detecting conductor current flow within them and of generating a corresponding voltage at their winding ends . Parallel to the winding of differential coil 12, a resistance R3 is inserted which allows to adjust the sensitivity of the current transformer and, similarly, a resistance R4 is inserted parallel to overvoltage coil 11.

The overload current is detected by having one only of the two power cables of the electrical appliance pass into coil 11, at whose ends a value will hence be read which changes whenever there is a variation in the power absorption of the electrical appliance connected to the socket. The current at the ends of coil 11 is rectified in a rectifier 13 and then sent to microcontroller 6 for reading and comparing against a preset value corresponding to the maximum admissible load in the socket. Should the measured current exceed the set limit value, the microcontroller deactivates microrelay 9 and the socket returns into its rest position.

The differential current due to power leakages in the electrical appliance is instead measured by causing both power cables of the electrical appliance to pass into coil 12, at whose ends a value normally equal to 0 will hence be read, except in the presence of power leakages in the appliance connected to the socket. In this case, too, the current at the ends of coil 12 is rectified in a rectifier 14 and then sent to microcontroller 6 for reading and comparing against a preset value corresponding to the maximum admissible leakage current in the appliances connected to the socket. Should the measured current exceed the set limit value, the microcontroller immediately deactivates microrelay 9 and the socket returns into its rest position.

The safety electrical socket according to the present invention, in addition to its independentIy-considered positive features described above, is also particularly well-suited to be used in multiple units for the building of electrical . systems, already known per se, wherein the loads existing in the individual sockets are controlled and selected according to a preset programme which employs a communication protocol known per se. An example of such a standard communication protocol is the communication network called XlO.

As a matter of fact, the reckoning capabilities of microcontroller 6 are sufficient to manage a "communication" between the sockets, using microwaves channelled into the electric network of the system, according to a preset programme which is stored in the microcontroller, said programme being of course changeable according to the user's requirements. In particular, it is thereby possible to carry out the monitoring of the total loads absorbed by the system, both in order to limit consumption, and to avoid power cuts in case the absorbed power exceeds the maximum admissible one. For this purpose, each of the individual sockets of the system is initially attributed a priority index.

When the microcontrollers of the individual sockets of the system detect the overall exceeding of the threshold of maximum admissible power for the system, among all the sockets active at that time, the operation of the socket having the lower priority index (for example a hair-dryer) is immediately discontinued, preserving instead the operation of those with a higher priority index (for example a washing machine) . This type of check, based on a priority index, is performed when the exceeding of the maximum admissible power is due to a time change of the absorption of an individual electrical appliance (for example when a washing machine begins the heating cycle) . When the exceeding of the maximum power instead occurs due to the introduction of a new electrical appliance, it is also possible to activate a different type of check, according whereto the microcalculator existing in the respective socket performs a short trial supply to detect the absorption of the new appliance and hence does not proceed to power activation until the overall power absorbed by the other active sockets drops to a value compatible with the load of the new energy-absorbing electrical appliance.

Of course other types of socket operation control and selection are anyhow possible, depending on the user's specific requirements, those described above having only an exemplifying purpose. For example, it is possible to provide for the user to be able - through a small control unit arranged in the proximity of the general switches - to choose the ways of action most suited to him, in addition to attributing the relevant priority index to each socket. For example, in the last case illustrated above, in order to directly exclude the new load regardless of the priority index of the affected socket, or to temporarily deactivate one or more electrical appliances having lower priority to be able to keep the new appliance active. The present invention has been described with reference to some preferred embodiments of the same, but it is evident that the scope of protection of the invention is in no way limited by such description, but comprises also all possible variants and improvements which are obvious to a person skilled in the field with knowledge of the invention and which are considered included in the definitions provided in the attached claims.

Claims

1) Safety electrical socket characterised in that it comprises a low-voltage electronic circuit for the recognition of the type of electrical appliance connected to the socket, a microrelay allowing the switching of the socket terminals between said low-voltage circuit and the mains voltage, and a microcontroller capable of picking up the signals coming from said appliance-recognition circuit and of activating said microrelay for connecting said socket to the mains voltage only when the appliance is recognised as an electrical appliance.

2) Safety electrical socket as claimed in claim 1) , wherein said circuit for the recognition of the type of electrical appliance comprises a primary circuit which connects in series a low-voltage, direct-current supply, the socket terminals and a first section of a photocoupler, and a secondary circuit which connects in series a second section of the photocoupler and said microcontroller.

3) Safety electrical socket as claimed in claim 2), wherein the first section of the photocoupler consists of a photodiode and the second section of the photocoupler consists of a phototriac, and wherein said photodiode is polarised by the current circulating in the primary circuit when the resistance at the socket terminals falls within the range of the resistances typical of electrical appliances, while it is not polarised when the resistance at the socket terminals falls within the range of the resistances typical of the human body.

4) Safety electrical socket as claimed in any one of the previous claims, wherein said low-voltage, electronic circuit also comprises a circuit for the detection of short-circuit conditions of the appliance connected to the socket terminals.

5) Safety electrical socket as claimed in claim 4) , wherein said circuit for the detection of short-circuits comprises a primary circuit which connects in series a low- voltage, direct-current supply, the socket terminals, a current- adjusting diode and a first section of a photocoupler, and a secondary circuit which connects in series a second section of the photocoupler and said microcontroller. 6) Safety electrical socket as claimed in claim 4) , further comprising a magnetothermic protection circuit.

7) Safety electrical socket as claimed in claim 6) , wherein said magnetothermic protection circuit comprises an overvoltage coil into which one of the two power cables of the electrical appliance runs, and the voltage signal at the ends of said coil - suitably rectified - is sent to said microcontroller .

8) Safety electrical socket as claimed in claim 7) , wherein said microcontroller deactivates said microrelay when the voltage value at the ends of said overvoltage coil exceeds a preset reference value equal to the maximum admissible load of said socket .

9) Safety electrical socket as claimed in claim 4) or 6) , further comprising a differential protection circuit .

10) Safety electrical socket as claimed in claim 9) , wherein said differential protection circuit comprises a differential coil into which both power cables of the electrical appliance run, and the voltage signal at the ends of said coil - suitably rectified - is sent to said microcontroller.

11) Safety electrical socket as claimed in claim 7) , wherein said microcontroller deactivates said microrelay when the voltage value at the ends of said differential coil exceeds a preset reference value equal to the maximum admissible leakage on the electrical appliances connected to said socket.

12) Use of two or more safety electrical sockets as claimed in any one of the preceding claims, in an electric system with automatic control and selection of the electric loads absorbed by said sockets . 13) Use of safety electrical sockets as claimed in claim 12) , wherein in the microcontroller of said sockets a priority index is introduced and, in case of exceeding the maximum admissible power for the system, the sockets are deactivated starting from those having a lower priority index. 14) Use of safety electrical sockets as claimed in claim 12) , wherein upon introduction of a new electrical appliance into one of said sockets, the relevant microcontroller proceeds firstly to a temporary activation of the socket for detecting the absorption of said new electrical appliance and then to the final activation of the socket only when the load of the new electrical appliance, added to the total loads existing at that time on the system, does not exceed the maximum admissible power for the system.

15) Use of safety electrical sockets as claimed in claim 14) , wherein the final activation of the socket wherein said new electrical appliance is introduced is, alternatively, accomplished by deactivating one or more sockets having a lower priority index, or, delayed until a drop of the total load on the other sockets, depending on a programme preset by the user.

16) Use of electrical sockets as claimed in any one of claims from 12) to 15) , wherein the pre-programtning of said sockets occurs through a single control unit, preferably arranged in the proximity of the general switches of said system.