Electric switching device

Abstract

 An electric switching device (1) for a low voltage electric circuit, comprising:
- at least a first pole (2) having a first moving contact (4) which can be coupled to/decoupled from a corresponding first stationary contact (5), and a second pole (3) having a second moving contact (6), which can be coupled to/decoupled from a corresponding second stationary contact (7);
- first detection means adapted to detect a differential current between said first and second poles (2, 3), said first detection means being configured to operate independently from the voltage of said electric circuit.
The switching device comprises second detection means, which are adapted to detect an overcurrent flowing in at least one of said first and second poles (2, 3), and which comprise at least a current transformer (50) operatively connected to said at least one of said first and second poles (2, 3).

Description

[0001] The present invention relates to an electric switching device for a low voltage circuit having improved characteristics of overcurrent protection.

[0002] As known, electric switching devices used in low voltage electric circuits (that is for applications with nominal voltages up to 1000V AC / 1500V DC), for example circuit breakers, disconnectors, and contactors designated as "switching devices", are all devices designed to ensure the protection of electric circuits and the safety of the users of the electric circuits themselves, by intervening upon the detection of a failure condition.

[0003] Circuit breakers comprise one or more electric poles having at least a moving contact adapted to assume a first position in which it is coupled to a corresponding stationary contact (closed switching device), and a second position, in which it is decoupled from the corresponding stationary contact (open switching device).

[0004] The intervention of the switching devices against the occurrence of fault conditions is carried out through the separation of the moving contacts from the corresponding stationary contacts. As known, the switching devices are generally provided with means adapted to protect against the occurrence of critical differential currents between the poles of the switching devices themselves, caused by an earth leakage current (also known as residual current or imbalance current).

[0005] Furthermore, the switching devices are provided with means adapted to protect against the occurrence of electrical currents having a critical value higher than the nominal operating current; such overcurrents can be non instantaneous (when caused for example by an overload condition), or instantaneous (when caused for example by a short-circuit).

[0006] In the state of the art switching devices of the modular type (miniature circuit breakers) are known that implement, together with the protection against differential currents, the protection from overcurrents by means of magneto-thermal means, and for this reason are known as "residual current circuit breakers with overcurrent protection" (RCBO).

[0007] In particular, the protection from non-instantaneous overcurrents is carried out by a bimetallic element operatively connected to one or more poles, or phases, that are to be protected from overcurrents. In general, the bimetallic element is inserted along the path of the current flowing in a phase of the switching device. When the value of the current flowing through the bimetallic element exceeds a predetermined threshold, the bimetallic element flexes and operatively interacts with the moving contacts of the switching device, so as to cause the separation of the moving contacts themselves from the corresponding stationary contacts. Typically, the predetermined threshold for the current flowing through the bimetallic element is equal to the value of the nominal current plus about 45% of the value itself; further, the flowing of the current must be guaranteed with a tolerance on the nominal operating value equal to about 15%.

[0008] The intervention time necessary to the bimetallic element to open the switching device decreases as the overcurrent passing through it increases, according to a relationship described by a characteristic curve known as "inverse time characteristic curve".

[0009] Even though the bimetallic element fully achieves its intended function and is a particularly economic solution, it implies a number of disadvantages and challenges. In particular, the bimetallic element must be accurately calibrated in order to operate properly according to the current flowing through it. In particular, certain applications do not allow overcurrents that are 20% higher than the nominal operating current, even requiring a tolerance on the nominal operating value equal to about 15%. In this case, the calibration of the bimetallic element in a very narrow range is critical, and results in substantial discards in the production of the switching devices.

[0010] Furthermore, the bimetallic element is a particularly temperature-sensitive device, and therefore requires a compensation of the variations of the room temperature, which may be substantial when the switching device is installed in critical environments.

[0011] The objective of the present invention is to provide a switching device having overcurrent protection means that allow to overcome the disadvantages highlighted in the prior art, while adopting a particularly simple and economical solution.

[0012] Said object is achieved by an electric switching device for a low voltage electric circuit, comprising:

• at least a first pole having at least a first moving contact which can be coupled to/decoupled from a corresponding first stationary contact, and a second pole having at least a second moving contact which can be coupled to/decoupled from a corresponding second stationary contact;
• first detection means adapted to detecting a differential current between the first pole and the second poles, said first detection means being configured to operate independently from the voltage of the electric circuit.

[0013] The switching device comprises second detection means which are adapted to detect an overcurrent flowing in at least one of said first and second poles, and which comprise at least a current transformer operatively connected to said at least one of the first and second poles. The switching device according to the present invention will be described hereinafter by making reference to one of its embodiments as a miniature differential circuit breaker (of the modular type) provided with protection against overcurrent. The principles and technical solutions described in the course of the following description are to be understood in any event to be also valid for different types of switching device, such as for example molded case circuit breakers (MCCB).

[0014] Characteristics and advantages will become more apparent from the description of preferred, but not exclusive, embodiments of a switching device according to the present invention, as illustrated for exemplification purposes in the accompanying drawings; wherein:

• figure 1 schematically shows a switching device according to the present invention;
• figure 2 shows a block diagram of the electronic means for the overcurrent protection and used in the switching device of figure 1;
• figure 3 shows a block diagram of a circuit block used in a switching device according to the present invention (comprising the electronic means for the protection from differential currents and the electronic means for the protection from overcurrent);
• figure 4 illustrates a characteristic curve showing the dependence of an intervention time on the value of the overcurrent against which the intervention is required;
• figure 5 schematically shows a current transformer having a magnetic core with an air gap, used in a switching device according to the present invention.

[0015] Figure 1 schematically illustrates a circuit breaker 1 for a low voltage circuit, in particular a miniature circuit breaker 1, comprising a first pole 2 and a second pole 3. The first pole 2 comprises a first moving contact 4 which can be coupled to/decoupled from a corresponding first stationary contact 5; in turn, the second pole 3 comprises a second moving contact 6 which can be coupled to/decoupled from a corresponding second stationary contact 7.

[0016] The first pole 2 comprises a first electrical terminal 8 and a second electrical terminal 9, and the second pole 3 comprises a third electrical terminal 10 and a fourth electrical terminal 11. Such electrical terminals 8, 9, 10, 11 are adapted to electrically connect the first pole 2 and the second pole 3 to the electric circuit where circuit breaker 1 is installed; in particular, they are adapted to operatively connect a power supply source (LINE) to an electric load (LOAD) of the associated electric circuit, by means of the first pole 2 and the second pole 3.

[0017] It is to be set forth that the circuit breaker 1 according to the present invention may have a number of poles different than that illustrated in the example in figure 1.

[0018] The first moving contact 4 and the second moving contact 6 are operatively connected to an operating mechanism 12 adapted to cause the separation of the first and second moving contacts 4, 6 from the corresponding stationary contacts 5, 7 as a result of its actuation; the operating mechanism 12 is of the type known in the art, and will therefore not be described in detail.

[0019] The circuit breaker 1 comprises first detection means adapted to detect a differential current between the first pole 2 and the second pole 3.

[0020] The first detection means are operatively connected to the first moving contact 4 and the second moving contact 6 so as to cause the separation of the first and second moving contacts 4, 6 from the corresponding first and second stationary contacts 5, 7 upon the detection of a differential current between the first pole 2 and the second pole 3 greater than a predetermined intervention threshold, for example 0.03 A.

[0021] In particular, the first detection means are configured so as to cause the intervention of the actuating means 30 of circuit breaker 1. Such actuating means 30, of the type known in the state of the art, are adapted to operatively interact with the first moving contact 4 and the second moving contact 6 so as to cause the separation of the first and second moving contacts 4, 6 from the corresponding first and second stationary contacts 5, 7.

[0022] In the example illustrated in figure 1, the actuating means 30 are operatively connected to the operating mechanism 12, so as to cause the operation of the operating mechanism 12 itself, by means of its intervention.

[0023] As illustrated in figure 1, the first detection means comprise a differential current transformer 20 (or current summing transformer 20), operatively connected to the first pole 2 and the second pole 3, so as to generate an electric output signal S₁ that depends on the differential current between the first pole 2 and the second pole 3.

[0024] In particular, the differential current transformer 20 comprises a magnetic core 21 crossed by a part of the first pole 2 and a part of the second pole 3, which constitute the primary winding of the differential current transformer 20. A secondary winding 22 is wound around the magnetic core 21.

[0025] Under normal conditions of operation, the current flowing through the first pole 2 and the corresponding current flowing through the second pole 3 are equal in value; the magnetic fields generated by the two currents cancel each other and no electric signal is generated in the secondary winding 22.

[0026] At the occurrence of a differential current between the first pole 2 and the second pole 3, the unbalance between the current flowing through the first pole 2 and the current flowing through the second pole 3 generates a magnetic field that induces the electric signal S₁ in the secondary winding 22. The value of the electric signal S₁ is indicative of the value of the differential current between the first pole 2 and the second pole 3.

[0027] The first detection means comprise electronic means 23 which are adapted to receive in input the electric signal S₁, and which are configured so as to detect a differential current between the first pole 2 and the second pole 3 through the electric signal S₁. In particular, the electronic means 23 are configured to compare the electric signal S₁ received in input with a predetermined threshold value, so as to detect the presence of a differential current between the first pole 2 and the second pole 3 that is greater than the predetermined intervention threshold. When such predetermined threshold value is exceeded, the electronic means 23 are configured so as to output a control signal S₂.

[0028] Control signal S₂ is suitable for causing the intervention of the actuating means 30 on the operating mechanism 12, providing the actuating means 30 themselves with the energy necessary for their intervention.

[0029] In the circuit breaker 1 according to the present invention, the first detection means (and the corresponding actuating means 30) are configured in order to operate independently from the voltage of the electric circuit where circuit breaker 1 itself is installed; that is to say, to operate independently from the voltage applied to the first and third electric terminals 8, 10 or to the second and fourth electric terminals 9, 11, under operating conditions of circuit breaker 1.

[0030] In particular, the electronic means 23 are configured to operate using only the energy associated to the electric signal S₁ received in input. In practice, the electronic means 23 remain inactive, or quiescent, until the electric signal S₁ is sent to their input. Preferably, the electronic means 23 are realized by one or more electronic analog blocks.

[0031] Preferably, the circuit breaker 1 comprises test means 24 operatively connected to the first detection means so as to simulate the generation of a differential current between the first pole 2 and the second pole 3 that is greater than the predetermined intervention threshold. According to a preferred embodiment, test means 24 comprise a test button which realizes, when pressed, an electric circuit inside the circuit breaker 1 which is adapted to supply a voltage to a second primary winding 25 wound around magnetic core 21. The current that begins to flow in the second primary winding 25 as a result of the application of the voltage, induces a magnetic field suitable for generating the electric signal S₁ in the secondary winding 22.

[0032] The circuit breaker 1 according to the present invention further comprises second detection means adapted to detect an overcurrent flowing in at least one of the first pole 2 and second pole 3.

[0033] Overcurrent must be understood as a current with value exceeding the value of the nominal operating current. Overcurrents can be non-instantaneous (typically with a duration in time in the order of minutes), mainly caused by an overload condition; or can be instantaneous currents, caused for example by a short-circuit failure.

[0034] Second detection means are operatively connected to the first moving contact 4 and the second moving contact 6, so as to cause the separation of the first and second moving contacts 4, 6 themselves from the corresponding first and second stationary contacts 5, 7 as a result of the detection of an overcurrent greater than a predetermined intervention threshold. In particular, the second detection means are configured to cause the intervention of the actuating means 30 of the circuit breaker 1, the same actuating means 30 driven by the first detection means as previously described.

[0035] In this way, the same actuating means 30 are advantageously used to actuate both the protection against differential currents and overcurrents; alternatively, the second detection means can drive actuating means dedicated only to the protection against overcurrent, separated from the actuating means 30 dedicated only to the protection against differential currents.

[0036] The second detection means comprise at least a current transformer 50 operatively connected to the first pole 2 and/or the second pole 3 so as to output an electric signal S₃ depending on the current flowing in the first pole 2 or in the second pole 3.

[0037] In the circuit breaker 1 illustrated in figure 1, the first pole 2, or phase 2 of the circuit breaker 1, is protected against overcurrent by means of the current transformer 50. The second pole 3, or neutral 3, is without a current transformer 50; protection against overcurrent for the second pole 3 is in fact implemented indirectly by means of the current transformer 50 of the first pole 2, since that the first detection means guarantee equality between the current flowing through the first pole 2 and the second pole 3, with the exception of a differential current smaller than the predetermined intervention threshold.

[0038] Alternatively, both the first pole and second poles 2, 3 may be phases 2, 3 of the circuit breaker 1 protected against overcurrents by means of a first current transformer 50 and a second current transformer 50, respectively. Furthermore, some or all the poles of a circuit breaker 1 with more than two poles may be provided with protection against overcurrent (implemented by means of a respective current transformer 50). For example, a tripolar circuit breaker 1 may be configured with three phases, or a quadrupole circuit breaker 1 may be configured with three phases and neutral, or with four phases.

[0039] In the circuit breaker 1 illustrated in figure 1, the current transformer 50 comprises a magnetic core 51 crossed by a part of the first pole 2, which constitutes the primary winding of the current transformer 50 itself. A secondary winding 52 is wound around the magnetic core 51; a magnetic field is generated by a current flowing through the first pole 2 so as to induce the electric signal S₃ in the secondary winding 52 with a value indicative of the value of the current flowing through the first pole 2.

[0040] Preferably, the current transformer 50 is configured so that the electric signal S₃ output by means of the secondary winding 52 is in the same order of magnitude as the electric signal S₁ output by the differential current transformer 20, even though the value of the overcurrent flowing through the first pole 2 is much greater (many orders of magnitude) than the value of the differential current that may occur between the first pole and second poles 2, 3. According to a first solution, such aim is achieved by using a magnetic core 51 with magnetic permeability sufficiently low to generate the output signal S₃ with the same order of magnitude as the output signal S₁.

[0041] According to a second solution, shown schematically in figure 5, the current transformer 50 comprises a magnetic core 510 having an air gap 511 dimensioned so that the electric signal S₃ output by means of the secondary winding 52 is in the same order of magnitude as the output signal S₁. The use of the magnetic core 510 further simplifies the manufacturing process of the circuit breaker 1, since the electric conductors that realize a portion of the conduction path of the first pole 2 may be first inserted into the circuit breaker 1 and soldered to the respective electric terminals 8, 9 of the first pole 2. Thereafter, the magnetic core 510 is placed around a corresponding part of an electric conductor of the first pole 2 by inserting such part into the magnetic core 510 through the air gap 511.

[0042] The second detection means comprise electronic means 53 adapted to receive in input the electric signal S₃ output by the current transformer 50 and which are configured to detect an overcurrent flowing through the first pole 2, using the electric signal S₃. In particular, the electronic means 53 are configured to compare the electric signal S₃ received in input, preferably adjusted by means of an input block, with a predetermined threshold value, so as to detect the presence of an overcurrent greater than the predetermined intervention threshold.

[0043] If such predetermined threshold value is exceeded, the electronic means 53 are configured to output a control signal S₄.

[0044] Control signal S₄ is suitable for causing the intervention of the actuating means 30, which actuate the operating mechanism 12, supplying to the actuating means 30 themselves the energy necessary for intervening. Alternatively, the signal S₄ may be sent to other actuating means, dedicated only to protecting against overcurrent.

[0045] The second detection means are preferably also configured to operate independently from the voltage of the electric circuit where the circuit breaker 1 is installed. In particular, the electronic means 53 are configured to operate using only the energy of the electric signal S₃ receive in input. In practice, the electronic means 53 remain inactive or quiescent until the electric signal S₃ is sent to their input.

[0046] Such solution is advantageous since that the electronic means 53 may be implemented in a simple manner, without the provision for the circuit breaker 1 to have means suitable for drawing the voltage between the first pole and second pole 2, 3, and for adjusting such voltage in order to be applied to the electronic means 53.

[0047] According to a preferred embodiment, the electronic means 53 comprise a chain of electronic analog blocks.

[0048] Alternatively, the functionalities of the electronic analog blocks may be implemented with a digital electronic unit, such as an electronic processing unit, for example a micro-controller.

[0049] According to this solution, the current transformer 50 is configured to output the electric signal S₃ with sufficient energy to supply the digital electronic unit; an overcurrent flowing in the first pole 2 has a high value and therefore owns the necessary energy to generate an electric signal S₃ at the output of transformer 50 suitable for supplying the digital electronic unit.

[0050] Preferably, the electronic means 53 are configured so that the delay time between the receiving in input of the electric signal S₂ and the outputting of the control signal S₄ decreases as the value of the detected overcurrent increases. In particular, the dependence of the delay time on the value of the detected overcurrent is described by a characteristic curve with a decreasing trend (inverse time characteristic curve).

[0051] The delay in the generation of the control signal S₄ produces a delay in the intervention of the actuating means 30 on the operating mechanism 12 for causing the separation of the first and second moving contacts 4, 6 from the respective first and second stationary contacts 5, 7. The overcurrents flowing through the first pole 2 that are only slightly higher than the predetermined intervention threshold are therefore allowed also for long times, while overcurrents with increasing values are allowed for shorter times.

[0052] According to a first embodiment, the electronic means 53 are configured to implement only the protection from non-instantaneous overcurrents, which are mainly caused by overload conditions. Thus, the electronic means 53 can be implemented according to simple design specifications.

[0053] Figure 4 shows, for an exemplary but not limiting purpose, an inverse time characteristic curve 500 which describes the trend of the intervention time associated to the electronic means 53 configured to implement the protection from non instantaneous overcurrent; such inverse time characteristic curve 500 describes the intervention time of a bimetallic element, used in the prior art for the protection against non instantaneous overcurrent. In practice, the electronic means 53 are configured to simulate the intervention of the bimetallic element against currents caused by overload conditions.

[0054] According to such first embodiment, the circuit breaker 1 comprises, in addition to the actuating means 30, at least a release actuator 32 (of the type known in the prior art) connected to one or more poles of the circuit breaker itself, in such a way that the current that flows through the poles themselves (or a portion of said current) also flows through it. In particular, the release actuator 32 is inserted along the path of the respective phase 2 of the circuit breaker 1 and is configured to act on the operating mechanism 12 upon the occurrence of an instantaneous overcurrent, so as to cause the separation of the first and second moving contacts 4, 6 from the respective first and second stationary contacts 5, 7.

[0055] In the circuit breaker 1 illustrated in figure 1 is schematically depicted an electromagnetic release actuator 32 inserted along the conduction path of the first pole 2 of the circuit breaker 1.

[0056] According to a second embodiment, the electronic means 53 are configured to implement, in addition to the protection against non-instantaneous overcurrent, also the protection against instantaneous overcurrent, which are mainly due to short-circuit faults. In particular, the electronic means 53 must be configured so that the time delay between the detection of the instantaneous overcurrent and the generation in output of the control signal S₄ is sufficiently short to guarantee an effective intervention against an instantaneous type event.

[0057] In practice the electronic means 53 have the advantage of being configured to also simulate the intervention of the electromagnetic actuator 32 against an instantaneous overcurrent, and therefore the presence of the electromagnetic actuator 32 in circuit breaker 1 is not necessary. The described solution is particularly advantageous for applications where the predetermined intervention threshold against an instantaneous overcurrent is not much greater than the predetermined intervention threshold for non-instantaneous overcurrent; for example, reference can be made to an application where the intervention threshold against an instantaneous overcurrent is equal to twice the value of the nominal operating current.

[0058] Such applications avoid the use of electromagnetic actuators 32 for intervening against instantaneous overcurrent, while not placing an excessive burden on the design specifications of the electronic means 53.

[0059] A non-limiting example of the electronic means 53, which can be used in the circuit breaker 1 according to the present invention, is described in detail by making reference to the block diagram illustrated in figure 2. The electronic means 53 in figure 2 comprise a chain of three circuit blocks 54, 55, 56 operatively connected to each other. The first block 54, or input block 54, receives in input the electric signal S₃ output by the current transformer 50, and comprises an adjustment circuit having preferably simple electronic elements such as diodes, resistors, and capacitors; the adjustment circuit is configured to conveniently adjust the electric signal S₃.

[0060] The adjusted electric signal S₃ is sent from the input block 54 to the second circuit block 55, or energy accumulation block 55, which comprises electronic means to accumulate the energy associated to the adjusted electric signal S₃. The third circuit block 56, or output block 56, is connected to the energy accumulation block 55 and comprises a comparison device, preferably a voltage detector, which receives in input the energy accumulated in the energy accumulation block 55 in order to compare the value of the adjusted electric signal S₃ to a predetermined threshold value.

[0061] The output block 56 is configured to output the energy received from the energy accumulation block 55 (thus outputting the control signal S₄ for the actuating means 30), when the energy received in input corresponds to a value of the adjusted electric signal S₃ greater than the predetermined threshold of the comparator device.

[0062] The input block 54 is designed so that the adjusted electric signal S₃ is greater than the threshold of the comparator device of the output block 56 when an overcurrent flowing through the first pole 2 of the circuit breaker 1 is greater than the predetermined intervention threshold.

[0063] It is to be set forth that the energy output by the energy accumulation block 55 reaches the predetermined threshold for generating control signal S₄ faster for larger values of the adjusted electric signal S₃. In this way, the time delay between the application of electric signal S₃ at the input block 54 and the generation of the control signal S₄ at output block 56 decreases as the value of the electric signal S₃ increases, and thus such time delay decreases as the value of the detected overcurrent increases.

[0064] Advantageously according to a preferred embodiment, the electronic means 23 of the first detection means and the electronic means 53 of the second detection means operate in parallel in the same circuit block 100 (depicted schematically in figure 1), sharing at least an output block of the circuit block 100 itself.

[0065] Figure 3 illustrates a non-limiting example of the circuit block 100, wherein the electronic means 23 for the protection against differential current and the electronic means 53 shown in figure 2 are present; such electronic means 23 and 53 operate in parallel sharing the output block 56.

[0066] In practice the electronic means 23 realize a first processing branch for the electric signal S₁ received in input, while the second electronic means 53 realize a second processing branch for the electric signal S₃ received in input. The first and second processing branches operate in parallel independently to generate the control signal S₂ and the control signal S₄ by means of the same output block 56 of the circuit block.

[0067] In particular, the electronic means 23 comprise at least a circuit block for adjusting the electric signal S₁; said adjustment block is designed so that the adjusted signal S₁ exceeds the threshold of the comparator device of output block 56 when the differential current present between the first pole and second poles 2, 3 is greater than the predetermined intervention threshold.

[0068] Preferably, the circuit breaker 1 comprises test means 57 operatively connected to the second detection means in order to simulate the occurrence of an overcurrent greater than the predetermined intervention threshold. According to a preferred embodiment, the test means 57 comprise a test button which, as a result of being activated, realizes an electric circuit inside the circuit breaker 1 adapted to apply a voltage to a second primary winding 58 wound around the magnetic core 51. The current that begins to flow in the second primary winding 58 as a result of the application of the voltage induces a magnetic field suitable for generating the electric signal S₃ in the first secondary winding 52.

[0069] In practice it has been observed that the circuit breaker 1 according to the present invention fully achieves the pre-established objectives. The protection from overcurrent, and in particular from non-instantaneous overcurrent caused by an overload, is carried out by using the current transformer 50 which, unlike a bimetallic element, does not need to be calibrated and functions substantially independently of environmental temperature.

[0070] Furthermore, where provided for, the current transformer 50 is also used to protect against instantaneous overcurrent caused by short-circuit faults, avoiding the use of electromagnetic actuators dedicated to protecting against short-circuit current.

[0071] The solution described is particularly simple and economical to implement. For example, the use of the same actuating means 30 to implement the protection against differential current and overcurrent, as well as the fact of implementing the electronic means 23 and the electronic means 53 in the same circuit block 100, as the branches that operate in parallel sharing at least the output block of circuit block 100 itself, allow to optimize the available resources in order to obtain a particularly simple and economical solution.

[0072] The solutions described here may be subjected to various modifications and variants, all of which are within the scope of the present invention. For example, it must be pointed out that unlike the example illustrated in figure 1, the electronic means 23 and the electronic means 53 may belong to two completely separate circuit blocks; and/or the actuating means controlled by the electronic means 23 and the electronic means 53 may be different.

Claims

1. An electric switching device (1) for a low voltage electric circuit, comprising:

- at least a first pole (2) having at least a first moving contact (4) which can be coupled to/decoupled from a corresponding first stationary contact (5), and a second pole (3) having at least a second moving contact (6) which can be coupled to/decoupled from a corresponding second stationary contact (7);

- first detection means adapted to detect a differential current between said first and second poles (2, 3), said first detection means being configured to operate independently from the voltage of said electric circuit;
characterized in that it comprises second detection means which are adapted to detect an overcurrent flowing in at least one of said first and second poles (2, 3), and which comprise at least a current transformer (50) operatively connected to said at least one of said first and second poles (2, 3).

2. The switching device (1) according to claim 1, characterized in that said second detection means are configured to operate independently from the voltage of said electric circuit.

3. The switching device (1) according to one or more of the preceding claims, characterized in that said second detection means comprise first electronic means (53) which are adapted to receive in input an electric signal (S₃) output by the current transformer (50) and which are configured so as to detect said overcurrent using said output electric signal (S₃).

4. The switching device (1) according to claim 3, characterized in that it comprises actuating means (30) adapted to operatively interact with said first and second moving contacts (4, 6) so as to cause the separation of said first and second moving contacts (4, 6) from the corresponding first and second stationary contacts (5, 7), said first electronic means (53) being configured to output a control signal (S₄) adapted to control the intervention of said actuating means (30) to cause the separation of said first and second moving contacts (4, 6) from the corresponding first and second stationary contacts (5, 7) when the detected overcurrent exceeds a predetermined threshold.

5. The switching device (1) according to claim 4, characterized in that said first electronic means (53) are configured to operate using the energy associated with the output signal (S₃) of the current transformer (50).

6. The switching device (1) according to one or more of the preceding claims, characterized in that said at least a current transformer (50) comprises a magnetic core (510) having at least an air gap (511).

7. The device according to claim 5, characterized in that said first electronic means (53) comprise at least a digital electronic unit adapted to be supplied by said output signal (S₃) of the current transformer (50).

8. The switching device (1) according to one or more of the preceding claims, characterized in that said first electronic means (53) are configured so that the delay time that elapses between the receiving in input of said electric signal (S₃) output by the current transformer (50) and the outputting of the control signal (S₄) decreases when the value of the detected overcurrent increases.

9. The switching device (1) according to one or more of the preceding claims, characterized in that it comprises at least a trip actuator (32) connected to said at least one of said first and second poles (2, 3), said trip actuator (32) being operatively connected to said first and second moving contacts (4, 6) so as to cause the separation of said first and second moving contacts (4, 5) from the corresponding first and second stationary contacts (5, 7) following the occurrence of an instantaneous overcurrent.

10. The switching device (1) according to one or more of the preceding claims, characterized in that it comprises test means (57) operatively connected to said second detection means so as to simulate the occurrence of said overcurrent.

11. The switching device (1) according to one or more of the preceding claims, characterized in that said first detection means are configured so as to control the intervention of said actuating means (30) to cause the separation of said first and second moving contacts (4, 6) from the corresponding first and second stationary contacts (5, 7) following the detection of a differential current between said first and second poles (2, 3) exceeding a predetermined threshold.

12. The switching device (1) according to claim 11, characterized in that said first detection means comprise:

- a differential current transformer (20) operatively connected to said first and second poles (2, 3);

- second electronic means (23) which are adapted to receive in input an electric signal (S₁) output by the differential current transformer (20) and which are adapted to detect said differential current between said first and second poles (2, 3) using said output electric signal (S₁);
said second electronic means (23) being configured to output a control signal (S₂) adapted to control the intervention of said actuating means (30) to cause the separation of said first and second moving contacts (4, 6) from the corresponding first and second stationary contacts (5, 7) when the detected differential current exceeds the predetermined threshold.

13. The switching device (1) according to claim 12, characterized in that said second electronic means (23) and said first electronic means (53) operate in parallel in a same circuit block (100) sharing at least one output block (56) of said circuit block (100).

Drawing