DESCRIPTION

The present description relates to the technical field of electrical installations and, more particularly, concerns a test circuit for a residual current circuit- breaker .

As is known, a residual current circuit-breaker comprises a safety system which upon detection of a leakage current in the load circuit is configured to switch the residual current circuit-breaker into the on state, in practice resulting in the switch being tripped.

Test circuits for residual current circuit-breakers are known of comprising a test button provided to allow a user to check the proper functioning of the aforesaid safety system and thus of the residual current circuit- breaker. When pressed by a user the test button is such as to connect a test resistance between an energised branch circuit i.e. a phase branch circuit and a neutral branch circuit so as to simulate a leakage current.

Normally, it is recommended that users activate the test button at least once a month to check the correct operation of the residual current circuit-breaker.

However, it has been observed that users often forget to perform the above operation and this results in a situation of potential risk for said users. In order to reduce the above risk, residual current circuit-breaker switches have been developed which are fitted with a counter and an optical or acoustic signalling device adapted to signal the need to perform the test of the residual current circuit-breaker if this is not done within a preset time interval. A residual current circuit-breaker of the type indicated above is for example described in the patent EP 0665623 Bl . However, it has been observed that in the residual current circuit-breaker described in the patent EP 0665623 Bl an interruption of the mains voltage automatically determines a reset of the counter. This causes a safety problem in localities where for example there are frequent interruptions of the mains voltage. In fact, if the time interval between two consecutive interruptions is less than the aforesaid preset time interval, there would be no signalling of a prolonged failure to press the test button, which would nullify the function of the optical or acoustic device signalling the need/recommendation to perform the test. The same problem would occur should the circuit breaker be opened manually .

The document W02004 / 111665 Al describes a complex solution which provides that the pressing of a test button be detected by a processor which in turn controls a relay output in order to switch off the power supply to an electrical load.

The document W02007 / 143576 A2 describes a complex solution of a circuit breaker with micro controller with an auto-test capacity which can be connected to a remote monitoring device in order to communicate to the latter the results of the tests run.

The object of this description is to provide a solution which makes it possible to overcome all or some of the drawbacks described above with reference to the document of the prior art EP 0665623 Bl and which is at the same time such as to limit the cost of said solution.

Such object is achieved by means of a test circuit for a residual current circuit-breaker as generally defined in claim 1. Preferred and advantageous embodiments of the aforesaid test circuit are defined in the appended dependent claims.

The invention will be clearer to understand from the following detailed description of its particular embodiments, made by way of a non-limiting example with reference to the appended drawings, wherein:

-figure 1 is a circuit diagram of a residual current circuit-breaker comprising an embedded test circuit; and

-figure 2 is a three dimensional view of the residual current circuit-breaker in the diagram in figure 1.

In the drawings, elements which are the same or similar will be indicated using the same reference numerals .

With reference to figure 1 a non-limiting embodiment of a residual current circuit-breaker 10 comprising a test circuit 20 is shown. In the example shown, the residual current circuit-breaker 10 comprises a container body 16 and the test device 20 is housed in the container body 16. The aforesaid container body 16 is conveniently made of electrically insulating material, such as hard plastic. The container body 16 is for example intended to be installed on a mounting rail inside an electrical switchboard .

The residual current circuit-breaker 10 is used to connect or disconnect from each other a mains power supply 3, such as an electricity distribution network, and a load electrical network 13, such as a home network to which various utility devices are connected.

The residual current circuit-breaker 10 is adapted to interrupt a neutral branch circuit 1, 11 and a phase branch circuit 2, 12 upon detection of a leakage current. The neutral branch circuit 1, 11 comprises for example a first conductor 1 and a second conductor 11. Also the phase branch circuit 2, 12 comprises for example a first conductor 2 and a second conductor 12. In one embodiment variant, several phase branch circuits 2, 12 may be provided for, for example three phase circuit branches.

In the particular example shown in figure 1 by way of a non-limiting example, the residual current circuit- breaker 10 comprises a first pair of terminals Tl and T2 connected to the mains power supply 3 and further comprises a second pair of terminals Til and T12 connected to the load electrical network 13. The above connection mode is the most frequent, as conventionally the terminals of a circuit breaker placed higher up are connected to the mains power supply 3 and those placed lower down are connected to the load electrical network 13. However, it is possible to reverse this connection mode, thereby connecting the terminals placed higher up to the load electrical network 13 and those placed lower down to the mains power supply 3.

In the example in Figure 1, the residual current circuit-breaker 10 further comprises a measuring toroid 15 having a primary winding crossed by the neutral branch circuit 1,11 and the phase branch circuit 2,12 and having a secondary winding electrically connected to a trip device 14, for example of the type known per se; the residual current circuit-breaker 10 comprises in the example two switching elements CI and C2 sensitive to the trip device 14, so that these, starting from the off state are brought into the on state by the trip device 14, upon detection by the measuring toroid 15 of a leakage current or rather of a current imbalance between the phase branch circuit 1, 11 and the neutral branch circuit 2, 12 due to a leakage current. For example, each of the two switching elements CI, C2 comprises a fixed contact element and a mobile contact element, wherein the mobile contact elements are sensitive to the trip device 14. In a manner known per se, the mobile contact elements may also be moved by a control lever 28 (figure 2) , for example manually operated and/or motor-driven, to turn on and off the residual current circuit-breaker 10.

In the example described, the switching element CI makes it possible to connect /disconnect the first 1 and the second conductor 11 of the neutral branch circuit from each other while the switching element C2 makes it possible to connect /disconnect the first 2 and the second conductor 12 of the phase branch circuit.

The test circuit 20 comprises:

- a first input circuit node Nl electrically connected to the neutral branch circuit 1, 11;

- a second input circuit node N2 electrically connected, to the phase branch circuit 2, 12;

- a test resistance Rtest; - a test switch C3 operable by means of a test button 21 to connect the test resistance Rtest between the first Nl and the second N2 circuit node so as to simulate a leakage current .

For example, the test switch C3 is a normally open push button switch.

According to an advantageous embodiment, the pressing of the test button 21 is such as to determine the closing of the test switch C3 in order to directly create a closed path of current between the circuit nodes Nl, N2 which passes through the test resistance (Rtest) . Thus a relatively simple and safe circuit can be operated directly manually to simulate a fault current detectable by the measuring toroid 15.

According to an advantageous embodiment, the test circuit 20 further comprises a sectioning switch C4 operatively positioned between the input circuit nodes Nl, N2, sensitive to the trip device 14 and adapted to be opened by at the opening of the switching elements CI, C2 and closed at the closing the latter. In the example, the sectioning switch C4 advantageously makes it possible to disconnect the test circuit 20 in the case in which the mains power supply 3 is unusually connected to terminals Til and T12.

In the particular example shown in figure 1, it may be observed that the measuring toroid 15, and in particular its primary winding, is crossed by the neutral branch circuit 1, 11 and by the phase branch circuit 2,12 and the input circuit nodes Nl, N2 are positioned one downstream and the other upstream, of the measuring toroid 15.

The test circuit 20 comprises:

- an electronic control circuit 22 configured to be fed by the neutral circuit branch 1, 11 and by the phase circuit branch 2, 12 comprising an electronic time counter adapted to vary and store a time count value and to reset the time count value upon pressing of the test button 21;

- an optical and/or acoustic signalling device D5 controlled by the electronic control circuit 22 for providing an acoustic and/or optic signal upon reaching a given time count value by the electronic time counter.

According to a particularly advantageous embodiment, the electronic control circuit 22 is fed by a power supply current flowing through the test resistance (Rtest) .

According to a preferred embodiment the optical and/or acoustic signalling device D5 is, or comprises an LED diode .

Preferably, the optical or acoustic signalling device D5 is fed by the electronic control circuit 22.

The purpose of the electronic time counter is in practice to count the time elapsed since the last pressing of the test button 21. If the time period counted exceeds a given temporal count value (for example, corresponding to a month or 30 calendar days) the electronic control circuit 22 warns the user by means of the optical or acoustic signalling device D5: for example, in the case of a LED diode, provision may be made to turn it from the off state to the steady on state, or an intermittent on state or the colour of the optical radiation emitted may change etc. The embodiment providing for bringing the LED D5 from the off state to an intermittent on state upon exceeding the above given time count value is advantageous, if for example, a reduced on duty cycle is chosen for example less than 50% (or for example equal to or less than 25%) because it permits the current absorbed by the test circuit 20 to be limited .

The test circuit 20 is adapted to be fed with a mains voltage provided by the neutral branch circuit 1, 11 and by the phase branch circuit 2, 12.

In addition, the electronic time counter comprises a volatile memory adapted to store said count value and to reset it upon pressing of the test button 21 or in the absence of the aforesaid said supply voltage. The electronic control circuit 22 comprises a non-volatile memory and is programmed to periodically copy into the non-volatile memory the time count value stored in the volatile memory so as to store it even in the absence of supply voltage. Thus advantageously, the interruption of the supply voltage provided by the mains power supply 3, or the opening of the residual current circuit-breaker 10 does not result in the total loss of the temporal count value reached up to the moment of interruption or opening .

According to a particularly advantageous embodiment, the electronic control circuit 22 comprises a micro controller adapted to automatically switch from an off state caused by an interruption of the supply voltage or by the opening of the residual current circuit-breaker to an on state upon restoration of said mains voltage, or the closure of the residual current circuit-breaker and the micro controller is programmed to automatically copy in the volatile memory, the time count value stored in the non-volatile memory at the moment of passing from the off state to the on state. This way, it is possible to resume the count after an interruption of the supply voltage, or the closing of the residual current circuit- breaker 10, from a count value equal or close to the count value reached at the time of the interruption of the mains voltage or the opening of the residual current circuit-breaker .

According to a preferred embodiment, the microcontroller has an operating current of 200 μΑ or less and more preferably of 100 μΑ or less. In other words, in the above embodiments, the microcontroller is a low consumption microcontroller and therefore absorbs a current (i.e. the supply current flowing through the test resistance Rtest) that does not interfere with the operation of the residual current circuit-breaker 10 so as to reduce the level of safety or cause undesired intervention of the trip device 14. A non-limiting example of a low consumption microcontroller, provided with a volatile memory in the form of a RAM type data memory and a non-volatile memory in the form of a FLASH type programme memory, is the microcontroller currently produced by Microchip™ with the code PIC10F320.

According to an advantageous embodiment, the electronic control circuit 22 is programmed to periodically copy into the non-volatile memory the time count value stored in the volatile memory at intervals of not less than 30 minutes, preferably not less than 60 minutes, such as every 120 or 180 minutes. This way a contribution can be made to limiting the consumption of the test circuit 20, although the provision of a LED diode D5 adapted to flash upon exceeding the given time count value, as described above, represents the main contribution to limiting energy consumption.

As regards the electric diagram of the test circuit figure 1 it is to be noted that this is a particular implementation of a circuit made by way of a non-limiting example. In this implementation, the electronic control circuit 22 is a microcontroller fed between 0V (at the PIN called GND) and a DC voltage (at the PIN called Vdd) . In the example in Figure 1, the DC voltage is obtained from a rectifier circuit (single half-wave) Dl, D2, Rl, D3, Ql, R2 , CI, of the AC voltage. A signal input (at the pin called Inl) of the microcontroller is sensitive to the closing of the switch C3, so that the microcontroller can reset the volatile memory upon pressing the test button 21. The resistors R5 and R6 adjust the signal voltage at the pin Inl to the level required by the microcontroller, lastly the resistance R3 connected in series between the LED diode 15 and a signal output at the pin called outl makes it possible to set the value of the on current of the LED diode D5.

With reference to figure 1, in the embodiment represented therein, the test circuit 20 is directly integrated inside the residual current circuit-breaker 10, so as to form a single device, housed in a single container body 16, which in its most general form comprises :

-switching elements CI, C2 adapted to establish or interrupt an electrical connection in a neutral branch circuit 1, 11 and in a phase branch circuit 2,12;

-a trip device 14 adapted to control the switching elements CI, C2 to interrupt said electrical connection upon detection of a leakage current;

-the container body 16 adapted to house the switching elements CI, C2 and the trip device 14;

-a first Tl, T2 and a second Til, T12 pair of terminals .

The aforesaid residual current circuit-breaker 10 further comprises an integrated test circuit 20 comprising :

- a first input circuit node Nl electrically connected to the neutral branch circuit 1, 11;

- a second input circuit node N2 electrically connected, to the phase branch circuit 2, 12;

- a test resistance Rtest;

- a test switch C3 operable by means of a test button 21 to connect the test resistance (Rtest) between the first Nl and the second N2 circuit nodes so as to simulate a leakage current; - an electronic control circuit 22 configured to be fed by the neutral circuit branch 1,11 and by the phase circuit branch 2, 12, comprising an electronic time counter adapted to vary and store a time count value and reset it upon pressing of the test button 21;

- an optical or acoustic signalling device D5 controlled by the electronic control circuit 22 for providing an acoustic and/or optical signal upon reaching a given time count value by the electronic time counter; wherein:

- the electronic time counter comprises a volatile memory adapted to store said time count value and to reset it upon pressing of the test button 21 or in the absence of said supply voltage;

- the electronic control circuit 22 comprises a non ^¬ volatile memory and is programmed to periodically copy into the non-volatile memory the time count value stored in the volatile memory so as to store said count value even in the absence of mains voltage.

A practical embodiment of the residual current circuit-breaker of figure 1 is shown in figure 2, illustrating the container body (or housing 16), the pair of terminals Til, T12, an optical and/or acoustic signalling device D5 in the form of an LED diode set in the housing 16, a test button 21, a manual control lever 28.

According to a possible second embodiment, not shown in the drawings, the test circuit 20 described above may be part of a residual-current protection device or module external to a circuit breaker, for example, magnetothermic, and electro-mechanically coupled thereto to constitute a residual current circuit-breaker — for example a residual and magnetothermic current circuit- breaker group. For example, without thereby introducing any limitations, the above residual-current protection device could be a device of the type described and/or claimed in the patent EP2019407 Al .

Obviously, a person skilled in the art may make numerous modifications and variations to the test circuit described above so as to satisfy contingent and specific requirements while remaining within the sphere of protection of the invention as defined by the following claims .