Patent Description:
The device according to the invention is particularly, although not exclusively, applicable to the technical field of the design and production of what are known as low voltage electrical systems, that is to say systems having a nominal voltage of less than <NUM> V AC, such as private electrical systems in domestic or industrial environments. These systems typically comprise a plurality of electrical appliances that are supplied with alternating current from an electrical substation via a suitable line.

Under the current national regulations concerning the design of electrical systems, these systems must ensure the safety of persons and property and must operate correctly according to their specified use. For this purpose, electrical systems provide for the use of special safety devices, including what is known as a residual current device, designed to disconnect an electrical circuit of the system.

As is known, a residual current device is a device configured to cut off the flow of current in an electrical circuit of the system if the difference in current between the active conductors of the system is greater than or equal to a nominal tripping threshold (typically <NUM> mA for protection against direct contact), this difference in current corresponding to what is known as the leakage current towards earth of the system.

Factors contributing to the generation of the leakage current towards earth include an accidental earth contact of an active part of the system or of a live conducting body due to a fault, what are known as direct and indirect contacts, and permanent leakage towards earth of the system.

In the relevant technical field, "direct contact" is taken to mean the (accidental) contact of a person with an active part of the system, that is to say with a normally live part such as an active conductor, while "indirect contact" refers to the contact of a person with a conductive body which is normally insulated but has become live due to a fault. These contacts generate leakage currents towards earth of the resistive type, that is to say currents in phase with the system voltage.

On the other hand, permanent leakage currents towards earth of the system are practically constant currents created by the impedance, which is inevitably non-infinite, linking the conductors of the system to the earth node. In other words, such leakage is due to the very nature of the wiring and the aforementioned appliances, and is therefore unrelated to any fault in the system.

These permanent leakage currents have a resistive component, that is to say one in phase with the voltage applied to the system, although this component is negligible unless there is a serious loss of insulation, and a reactive component, particularly a capacitive component, created both by parasitic capacitances present between the phase wires and the earth of the system, and by noise filters which are installed in most electronic equipment at the present time, for reasons of electromagnetic compatibility. More specifically, in single-phase systems supplied with alternating current, electrical noise filters, called EMI filters, introduce capacitive leakage currents at mains frequency, usually with a value in the range from <NUM> to <NUM> mA.

The applicant has observed that the increasing use of electronic equipment in systems may cause the development of leakage currents towards earth with an overall value such that they cause untimely tripping of residual current devices, thus preventing the system from operating when there is no real fault in the system, in other words when there is no real situation of risk for a person.

To overcome this problem, there is a known way of dividing the electrical system into two or more parallel branches, so that the leakage towards earth of each branch is less than about a third of the nominal tripping threshold of the residual current device associated with it.

In the technical field to which the present invention relates, there is also a known way of producing special residual current devices designed to minimize the persistent problem of untimely tripping.

Examples of such circuit breakers are described in <CIT>.

However, the applicant has noticed that the "reinforced immunity" circuit breakers of <CIT> prove to be more structurally and functionally complex than ordinary residual current devices, and therefore more expensive, since they have to provide special means for performing the aforesaid subtraction between the currents, for example by using calculation units configured to process special-purpose algorithms.

An example of a residual current protection device is described in the patent application <CIT>. In particular, this residual current protection device comprises a residual current device, including a circuit breaker element and a toroid in series for measuring a differential current, and an impedance two-terminal network connected to the phase and neutral conductors of an electrical line, upstream and downstream of the toroid respectively. The residual current device and the bipolar impedance are therefore found to be intrinsically connected to one another, forming in a substantially inseparable manner the residual current protection device of <CIT>. Additionally, the applicant has noticed that the impedance two-terminal network inevitably forms a bypass circuit which electrically connects the phase conductor to the neutral conductor, even with the circuit breaker element open. This condition causes the potential of the neutral conductor to rise to that of the phase conductor, which evidently gives rise to safety problems in the electrical line.

Furthermore, the applicant has noticed that, in order to provide an electrical system, already having simple residual current devices, with "reinforced immunity" circuit breakers or residual current protection devices as mentioned above, it would inevitably be necessary to replace the residual current devices already present in the system, thus increasing the servicing and maintenance costs of the system.

An example of method and circuit arrangement with means for a leakage current compensation in a photovoltaic system with multiple differential current sensors is disclosed in <CIT>.

In the context of the present description and the claims, the following definitions have been adopted.

The expression "circuit of a single-phase electrical system" relates to a single-phase electrical system as a whole, or part of it, which is energized by a power supply device through a single-phase electrical line. The aforesaid circuit of a single-phase electrical system comprises a phase conductor and a neutral conductor.

The expression "differential current" relates to the difference between the current flowing in a phase conductor and that flowing in a neutral conductor of the circuit of a single-phase electrical system. This represents the current which is detected by a residual current device whose input is connected to a first and a second conductor of the single-phase electrical line, and whose output is connected to the phase and neutral conductors of the aforesaid circuit.

The expression "capacitive leakage current" relates to the total capacitive leakage current of the circuit of a single-phase electrical system formed by the sum of the leakage currents towards earth of the capacitive type generated by the phase and neutral conductors of the aforesaid circuit and by the loads present in it.

The problem underlying the present invention is that of providing a compensation device suitable for compensating a capacitive leakage current of a circuit of a single-phase electrical system, a circuit of a single-phase electrical system comprising such a device, and a method for compensating a capacitive leakage current of such a circuit structurally and functionally designed to overcome at least one drawback identified in the aforementioned prior art.

The applicant has also noticed that possible pulsed phenomena of atmospheric origin or arising from operation, such as excess voltages or, more generally, sudden variations of voltage or current, may create transitory leakage currents towards earth, which also cannot be related to faults of the system and/or situations of real danger for persons. Such a transient current, typically of the pulsed type, is also detected by the residual current device.

Furthermore, the applicant has noticed that the tolerances on the manufacture of a residual current device may give rise to tripping of the circuit breaker even at an root mean square (r. ) value of the differential current equal to about ¾ of the nominal tripping threshold, or in the range from ½ of the nominal tripping threshold to the nominal threshold itself, as stated by the relevant standards.

The applicant has therefore realized that, typically, a permanent leakage current value greater than, or equal to, ¾ of the nominal tripping threshold of the residual current device could cause untimely tripping of the circuit breaker. The applicant has also realized that a reduction of the tripping margin of the residual current device, due to the aforesaid permanent leakage current, as explained more fully below, may easily cause the untimely tripping of the residual current device if transient currents, even if small, occur as a result of rapid variations in the power supply voltage (due to atmospheric events, for example).

The untimely tripping of a residual current device may also be caused by the voltage variation due to the action of resetting the circuit breaker.

The applicant has therefore realized that the permanent leakage current is one of the main causes of the undesired phenomenon of untimely tripping of the residual current device.

In the context of this problem, one object of the invention is to provide a compensation device which can limit, or preferably eliminate, the phenomenon of untimely tripping of residual current devices.

A further object of the invention is to ensure continuity of service of an electrical system if there are no faults in the system and/or if there is no real danger for its user.

A further object of the invention is to provide a compensation device which does not compromise or reduce the safety of the circuit of an electrical system to which it is connected.

This problem is overcome, and at least one of these objects is achieved, by means of a compensation device, a circuit of a single-phase electrical system comprising such a compensation device, and a method for compensating a capacitive leakage current of a circuit of a single-phase electrical system carried out in accordance with the respective independent claims appended to the present description.

Preferred characteristics of the invention are defined in the dependent claims.

The features and further advantages of the invention will be more apparent from the following detailed description of some preferred but non-exclusive examples of embodiment thereof, illustrated, for the purposes of guidance and without restrictive intent, with reference to the attached drawings, in which:.

<FIG> shows a circuit <NUM> of a single-phase electrical system energized by a power supply device <NUM> through a single-phase electrical line <NUM>, in which ZL and ZN represent the line and neutral impedance of the single-phase electrical line <NUM>.

With reference to <FIG>, the reference numeral <NUM> indicates the whole of a compensation device for a circuit <NUM> of a single-phase electrical system carried out according to the present invention. The circuit <NUM> may be a single-phase electrical circuit.

According to one aspect of the invention, the single-phase electrical system may be identical with a consumer electrical system of an electrical power system (preferably a low voltage system). With reference to <FIG>, the circuit <NUM> comprises a phase conductor <NUM>, a neutral conductor <NUM> and, preferably, a protective conductor connected to earth (indicated by the reference numeral <NUM>).

The phase and neutral conductors <NUM>, <NUM> of the circuit <NUM> are connected, respectively, to a first conductor <NUM> and to a second conductor <NUM> (or corresponding branches) of a single-phase electrical line <NUM>, the second conductor <NUM> of the single-phase electrical line <NUM> being connected to earth, preferably in an electrical substation.

Preferably, a power supply device <NUM> is connected to the single-phase electrical line <NUM> to energize it.

According to one aspect of the invention, the second conductor <NUM> of the single-phase electrical line <NUM> is connected to earth near, or at, the power supply device <NUM> (this connection is shown, by way of example, as the node Tc in <FIG>).

With reference to <FIG>, Zt shows the impedance between the earth of the single-phase electrical system and the node Tc, that is to say between the node Tc and the earth <NUM>. Preferably, the impedance Zt is essentially negligible.

According to one aspect of the invention, the circuit <NUM> and single-phase electrical line <NUM> are of the low voltage type; that is to say, they are supplied with alternating current at a nominal voltage of not more than <NUM> V by the power supply device <NUM>. Preferably, the power supply device <NUM> applies a predetermined voltage to the circuit <NUM>, preferably a nominal voltage of <NUM> V AC at <NUM>, thus establishing a voltage between the phase conductor <NUM> and the neutral conductor <NUM>.

Preferably, the power supply device <NUM> is an electrical substation, particularly an electrical transformer substation designed to transform the voltage supplied from an intermediate voltage network to the supply levels of low voltage lines.

More preferably, the power supply device <NUM> is provided with a corresponding earthing system through which the second conductor <NUM> of the single-phase electrical line <NUM> is earthed.

In a more general embodiment of the invention, the power supply device <NUM> is a multiphase, particularly a three-phase, generator or transformer, in which the single-phase electrical line <NUM> is connected electrically to a phase terminal and to a neutral terminal (star centre) of the power supply device <NUM> through the first and second conductor <NUM>, <NUM> respectively.

In a preferred embodiment of the invention, the circuit <NUM> forms, with the single-phase electrical line <NUM> and with the power supply device <NUM>, an electrical system of the TT ("Terra-Terra", Earth-Earth) or TN ("Terra-Neutro", Earth-Neutral) type. In particular, the TT or TN electrical system is a single-phase system.

One or more loads <NUM> (represented in <FIG> by the equivalent load <NUM>) are connected to the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM> in such a way that they can be energized with alternating current (at <NUM> V, <NUM> for example) from the single-phase electrical line <NUM> through the conductors <NUM>, <NUM>.

In particular, the earths of the loads <NUM> are electrically connected to earth <NUM>, preferably via the protective conductor.

By way of example, the loads <NUM> may be electrical equipment or machines connected to the circuit <NUM> and intended to perform a specific function, particularly domestic appliances such as refrigerators, televisions and cookers.

The phase and neutral conductors <NUM>, <NUM> of the circuit <NUM> and the loads <NUM> connected to them have respective parasitic capacitances through which they generate capacitive leakage currents towards earth, the sum of which forms a capacitive leakage current ICD of the circuit <NUM>. In other words, leakage currents towards earth of the capacitive type are established through the aforesaid parasitic capacitances.

In the context of the present invention, the equivalent parasitic capacitance of the circuit <NUM> is indicated by the symbol CD, and, for the sake of simplicity, is defined as the sum of the parasitic capacitances present between the phase conductor <NUM> and the earth <NUM> with the parasitic capacitances of the loads <NUM>. The capacitance between the neutral conductor <NUM> and the earth <NUM> is, in fact, essentially irrelevant, since the current flowing through it is negligible (the voltage at the ends of this capacitance is essentially zero).

Regarding the capacitive leakage current ICD, this comprises the permanent capacitive leakage currents towards earth (which cannot be related to faults of the electrical system and/or situations of real danger for a person) and the transient capacitive leakage currents towards earth, generally pulsed, which may be related to abrupt variations in the voltage applied to the circuit <NUM>.

In the context of the present invention, the sum of the permanent capacitive leakage currents of the circuit <NUM> is defined as follows: permanent capacitive leakage current ICP. casein particular, the constant capacitive leakage current ICP is an alternating current, particularly a sinusoidal current, having a frequency fCP equal to that the power supply of the circuit <NUM> (<NUM>, for example). In particular, the permanent capacitive leakage current ICP is offset by <NUM>° in advance of the voltage applied to the circuit <NUM>.

The capacitive leakage current ICD may therefore be defined as an alternating current resulting from the sum of the permanent capacitive leakage current ICP with any transient (pulsed) capacitive leakage currents, that is to say: <MAT> where ICT represents the sum of the transient capacitive leakage currents.

According to one aspect of the invention, the capacitive leakage current ICD flows alternately from and towards earth (through the aforesaid parasitic capacitances). According to a further aspect of the invention, the capacitive leakage current ICD has a fundamental period TCD equal to the period (<NUM>/fCP) of the constant capacitive leakage current ICP.

Preferably, the circuit <NUM> comprises a residual current device <NUM> whose input is connected to the first and second conductor <NUM>, <NUM> of the single-phase electrical line <NUM> and whose output is connected to the phase conductor <NUM> and neutral conductor <NUM> of the circuit <NUM>.

According to one aspect of the invention, the residual current device <NUM> may be an ordinary safety device capable of cutting off the flow of electrical power in the circuit <NUM> in case of an earth fault. Consequently, no detailed description of the residual current device <NUM> will be given.

According to one aspect of the invention, the residual current device <NUM> is configured to detect differential current IΔ.

Preferably, the differential current IΔ represents the difference between the phase current IF flowing in the phase conductor <NUM> and the neutral current IN flowing in the neutral conductor <NUM> of the circuit <NUM>. In particular, the phase current IF is the electric current leaving the residual current device <NUM> and flowing in the phase conductor <NUM>, while the neutral current IN is the electric current entering the residual current device <NUM> and flowing in the neutral conductor <NUM> as shown in the circuit diagram of the figures attached to the description.

In an ideal condition, that is to say in the absence of leakage currents towards earth in the circuit <NUM>, the differential current IΔ detected by the circuit breaker <NUM> would be equal to zero. Differently, the presence of leakage currents towards earth in the circuit <NUM> creates an imbalance between the phase current IF and the neutral current IN, creating a differential current IΔ which is other than zero.

If the root mean square value of the differential current IΔ is greater than or equal to a predetermined threshold of the residual current device <NUM>, the latter is tripped, cutting off the flow of current in the circuit <NUM> and disconnecting both the phase conductor <NUM> and the neutral conductor <NUM>. This predetermined threshold is defined as the nominal tripping threshold IΔn (typically <NUM> mA for protection from direct contact).

As mentioned above, the manufacturing tolerances on the residual current device <NUM> may, in reality, cause the circuit breaker <NUM> to be tripped at root mean square values of the differential current IΔ equal to an actual tripping threshold IΔR, which is below the nominal tripping threshold IΔn. In particular, the actual tripping threshold IΔR of a residual current device <NUM> may have a value in the range from ½ IΔn to IΔn, typically equal to ¾ IΔn.

If there are no faults and/or no situation of real danger for a person, the neutral current IN is reduced by a value equal to the capacitive leakage current ICD. This results in an imbalance between the phase current IF and the neutral current IN, creating a differential current IΔ which is equal to ICD. In particular, in a normal operating condition of the circuit <NUM>, in which there are no excess voltages or other transient phenomena, the differential current IΔ detected by the residual current device <NUM> will not be zero, but will be equal to the permanent capacitive leakage current ICP; that is to say: <MAT>.

The difference between the actual tripping threshold IΔR and the permanent capacitive leakage current ICP will be defined as the tripping margin M of the residual current device <NUM>.

In other words, the tripping margin M may be equal to the value of an leakage current towards earth which is different from the permanent capacitive leakage current ICP and which, when added to the latter, will be capable of causing the residual current device <NUM> to trip.

<FIG> shows a vectorial representation of the differential current IΔ in the complex plane in a condition in which there are no faults and/or no situation of real danger for a person, and therefore the differential current IΔ is equal to the constant capacitive leakage current ICP. <FIG> also shows the actual tripping threshold IΔR in the form of a circumference defining an assured tripping region 11a of the residual current device <NUM> and a non-tripping region 11b inside the circumference.

It is evident from <FIG> that an r. value of the permanent capacitive leakage current ICP that is greater than, or equal to, the actual tripping threshold IΔR causes the untimely tripping of the residual current device <NUM>.

It should also be noted that an increase in the r. value of the permanent capacitive leakage current ICP corresponds to a reduction of the tripping margin M of the residual current device <NUM>, a fact which probably leads to an increase in the probability of untimely tripping of the residual current device <NUM>.

In the preferred embodiment of the invention, the compensation device <NUM> comprises a compensation circuit <NUM> provided with a first and a second terminal <NUM>, <NUM>. The compensation circuit <NUM> is designed to be connected to the neutral conductor <NUM> via the first terminal <NUM> and to an earthing system <NUM> via the second terminal <NUM>. Thus the neutral conductor <NUM> may be electrically connected to the aforesaid earthing system <NUM> through the compensation circuit <NUM>.

The circuit <NUM>, or the single-phase electrical system, may comprise the earthing system <NUM>. Preferably, the earthing system <NUM> is separate from an earthing system of the power supply device <NUM>.

Alternatively, the earthing system <NUM> is provided in the power supply device <NUM>.

According to one aspect of the invention, the compensation device <NUM> is connected to the circuit <NUM> downstream of the residual current device <NUM> with respect to the single-phase electrical line <NUM>. Preferably, the compensation device <NUM> is connected to the circuit <NUM> upstream of the loads <NUM> with respect to the single-phase electrical line <NUM>. With reference to <FIG>, the first terminal <NUM> is connected to the neutral conductor <NUM> downstream of the residual current device <NUM> and preferably upstream of the loads <NUM> with respect to the single-phase electrical line <NUM>.

The compensation circuit <NUM> is configured to generate a compensation current IC in such a way that it flows alternately from the neutral conductor <NUM> to earth and vice versa through the earthing system <NUM> when the first and second terminals <NUM>, <NUM> are connected, respectively, to the neutral conductor <NUM> and to the earthing system <NUM>, the compensation current IC having direction which is opposite that of the capacitive leakage current ICD.

In particular, the compensation current IC flows from the neutral conductor <NUM> towards earth and vice versa through the compensation circuit <NUM>.

In other words, the compensation circuit <NUM> is configured in such a way that the compensation current IC flows from the neutral conductor <NUM> towards earth when the capacitive leakage current ICD flows from earth towards the phase conductor <NUM>, and in such a way that the compensation current IC flows from earth towards the neutral conductor <NUM> when the capacitive leakage current ICD flows from the phase conductor <NUM> towards earth.

More preferably, the compensation current IC is in phase opposition to the capacitive leakage current ICD. In particular, the compensation current IC is substantially reactive.

According to one aspect of the invention, the compensation device <NUM> produces a compensation current IC which, in a first step, flows from the compensation circuit <NUM> to the neutral conductor <NUM> of the circuit <NUM>, through the first terminal <NUM>, and returns through the earthing system <NUM> after passing through the second conductor <NUM> of the single-phase electrical line <NUM> and the earth.

Instead, in a second step, the compensation current IC flows from the compensation circuit <NUM> towards earth, through the second terminal <NUM> and the earthing system <NUM>, and returns in the neutral conductor <NUM> of the circuit <NUM> after passing through the earth and the second conductor <NUM> of the single-phase electrical line <NUM>.

It should be noted that, by applying the principle of superposition of effects to the circuit diagram of <FIG>, we obtain a first and a second electrical meshes <NUM>, <NUM>', as represented in <FIG>, which show, respectively, the contribution of the compensation current IC and the contribution of the leakage current ICD. The equivalence of the electrical meshes <NUM> and <NUM>' is discussed below.

With reference to the figures, because of the presence of the compensation current IC we can rewrite the differential current IΔ detected by the residual current device <NUM> as follows: <MAT>.

In other words, according to one aspect of the invention, the differential current IΔ detected by the residual current device <NUM> is equal to the sum (particularly the vector sum) of the capacitive leakage current ICD and the compensation current IC. According to one aspect of the invention, the compensation circuit <NUM> is configured to generate the compensation current IC in such a way that the sum of the compensation current IC and the capacitive leakage current ICD has a smaller value than that of the capacitive leakage current ICD. Preferably, the intensity of the compensation current IC is such that the sum of the compensation current IC and the capacitive leakage current ICD has a smaller value than that of the capacitive leakage current ICD.

According to one aspect of the invention, the intensity of the sum of the compensation current IC and the capacitive leakage current ICD is smaller than the intensity of the capacitive leakage current ICD.

Preferably, the compensation current IC is generated in such a way that the point value (and/or r. value) of the sum of the compensation current IC and the capacitive leakage current ICD is smaller than the point value (and/or r. value) of the capacitive leakage current ICD.

Preferably, the compensation circuit <NUM> is configured to generate the compensation current IC in such a way that its intensity, particularly its point and/or r. value, is less than twice that of the capacitive leakage current ICD.

In other words, according to one aspect of the invention, the intensity of the compensation current IC is such that the value, particularly the r. value, of the differential current IΔ detected by the residual current device <NUM> is smaller than the value, particularly the r. value, of the capacitive leakage current ICD.

Because of these characteristics, the differential current IΔ detected by the residual current device <NUM>, that is to say the sum of the currents ICD and IC, has a (r. ) value smaller than that of the capacitive leakage current ICD, that is to say smaller compared with a condition in which no compensation is provided by the compensation current IC according to the invention, that is smaller compared with a circuit of an electrical system not equipped with the device <NUM>.

Thus the possibility of untimely tripping of the residual current device <NUM> is reduced.

In one embodiment of the invention, the instantaneous value of the compensation current IC generated by the compensation circuit <NUM> is proportional to the value of the capacitive leakage current ICD at that instant. In this case, allowing for the fact that the direction of the compensation current IC is opposite that of the capacitive leakage current ICD, the compensation current IC may be written as -K*ICD, where <NUM><K<<NUM>. Therefore the differential current IΔ detected by the residual current device <NUM> will have a value of (<NUM>-K)*ICD, that is to say: <MAT>.

For a compensation current IC having a suitable (r. ) value, the (r. ) value of the sum of the currents ICD and IC, that is to say the (r. ) value of (<NUM>-K)*ICD, will therefore be smaller than the (r. ) value defined by the capacitive leakage current ICD alone, thus allowing the r. value of the differential current IΔ detected by the residual current device <NUM> to be reduced.

Preferably, the instantaneous value of the compensation current IC is equal to that of the capacitive leakage current ICD at the same instant of time, so that the value of the differential current IΔ detected by the residual current device <NUM> is (essentially) made equal to zero.

In this case, the compensation device <NUM> faithfully reproduces the series defined by the power supply device <NUM> with the equivalent parasitic capacitance CD of the circuit <NUM> (assuming that ZN = ZL).

The first electrical mesh <NUM> of <FIG> may therefore be considered equivalent to the second electrical mesh <NUM>' of <FIG>. In other words, since the first and second meshes <NUM> and <NUM>' are equivalent, the respective currents are essentially equal.

It should also be noted that the compensation current IC increases the tripping margin M of the residual current device <NUM>, thus resolving the problem of untimely tripping of the residual current device <NUM>.

The compensation device <NUM> also makes it possible to resolve the problem of untimely tripping of a residual current device <NUM> without increasing the tripping time of the circuit breaker, thus keeping the safety of the electrical system unchanged. Advantageously, the provision of a connection between the compensation device <NUM> and the circuit <NUM> downstream of the residual current device <NUM> prevents the formation of a bridge between the first conductor <NUM> of the single-phase electrical line <NUM> and the circuit <NUM> which would allow the electrical power from the power supply device <NUM> to avoid and bypass the residual current device <NUM>, thus energizing the circuit <NUM> regardless of whether the circuit breaker was open or closed. Therefore the safety of the electrical system is not reduced.

In one embodiment of the invention, the direction of the compensation current IC is opposite that of the capacitive leakage current ICD for a substantial portion of the fundamental period TCD of the capacitive leakage current ICD. Preferably, the aforesaid substantial portion of the fundamental period TCD is at least <NUM>% of the latter. More preferably, the aforesaid substantial portion is at least <NUM>% of the fundamental period TCD.

In this case, although the compensation circuit <NUM> does not generate a capacitive leakage current ICD opposed to the capacitive leakage current ICD for each instant of time, it still provides sufficient compensation of the capacitive leakage current ICD to prevent the untimely tripping of the residual current device <NUM>.

In particular, it should be noted that the reduction of the r. value of the differential current IΔ detected by the residual current device <NUM> becomes greater as the intensity, particularly the r. value, of the compensation current IC approaches the intensity, particularly the r. value, of the capacitive leakage current ICD.

In this context, the compensation device <NUM> may provide input means <NUM> such as switches, selectors and/or software configurations, which an operator may use to carry out a procedure of calibrating the compensation current IC, modifying its r.

In particular, the input means <NUM> are arranged to regulate the r. value of the compensation current IC in such a way that it is substantially equal to the r. value of the capacitive leakage current ICD.

This calibration procedure includes a first step of measuring the r. value of the differential current IΔ detected by the residual current device <NUM>, for example by means of a clamp-on ammeter suitable for measuring the leakage currents of an electrical system. The calibration procedure then provides for the generation of a compensation current IC having a zero value, by means of the compensation circuit <NUM>.

A third step of the calibration procedure provides for the increase of the r. value of the compensation current IC generated by the compensation circuit <NUM>, using the aforesaid input means <NUM>, until the r. value of the differential current IΔ measured by the clamp-on ammeter reaches a minimum.

Alternatively, the input means <NUM> of the compensation device <NUM> may be used to set an r. value of the compensation current IC at <NUM>/<NUM> of the nominal tripping threshold IΔn.

In particular, <NUM>/<NUM> IΔn is the value of the compensation current Ic which maximizes the tripping margin M for an unknown capacitive leakage current ICD which is smaller than <NUM>/<NUM> IΔn. In many cases, this value is found to be sufficient to overcome the problem of untimely tripping of the residual current device <NUM>.

With reference to <FIG>, it may be seen that, in the absence of transient capacitive leakage currents in the circuit <NUM>, the compensation current IC still makes it possible to reduce the contribution made by the permanent capacitive leakage current ICP to the determination of the differential current IΔ, thus limiting or entirely resolving the persistent problem of the untimely tripping of the residual current device <NUM>.

In order to provide the functions described above, the compensation device <NUM> may have the following detailed structure.

In a preferred embodiment of the invention, shown by way of example in <FIG>, the compensation circuit <NUM> comprises a third terminal <NUM> which can be connected to the phase conductor <NUM>, and is configured to use the voltage present between the third terminal <NUM> and the first terminal <NUM> to generate the compensation current IC. In the context of the present invention, the expression "to use a voltage" may also be interpreted as meaning "to measure, or detect, at least a part of this voltage".

Preferably, the first and third terminals <NUM>, <NUM> are connected, respectively, to the neutral conductor <NUM> and the phase conductor <NUM>, and the voltage present between the third terminal <NUM> and the first terminal <NUM> represents, and in particular is proportional to, the voltage between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>.

Thus the compensation circuit <NUM> proves to be particularly suitable for generating a compensation current IC including a first component having a frequency equal to that of the nominal voltage applied to the circuit <NUM>, and possibly a second component which is transient, being pulsed for example. Therefore the compensation current IC is capable of limiting, notably, not only the permanent capacitive leakage current ICP, but also the transient capacitive leakage currents, greatly reducing or eliminating the problem of untimely tripping of the residual current device <NUM>.

According to one aspect of the invention, the compensation device <NUM> may also comprise a changeover circuit arranged to switch the connections of the first and third terminals <NUM>, <NUM> of the compensation circuit <NUM> if they are connected to the phase conductor <NUM> and neutral conductor <NUM>, respectively, of the circuit <NUM>. This ensures the correct connection of the terminals of the compensation device <NUM>, that is to say the connection of the first terminal <NUM> to the neutral conductor <NUM> and the connection of the third terminal <NUM> to the phase conductor <NUM> of the circuit <NUM>.

According to one aspect of the invention, the compensation circuit <NUM> may comprise a voltage generator <NUM> for generating a compensation voltage Vc between its ends.

Preferably, the compensation voltage Vc is generated between a first end of the voltage generator <NUM> connected (directly or indirectly) to the first terminal <NUM> and a second end of the voltage generator <NUM> connected (directly or indirectly) to the second terminal <NUM> of the compensation circuit <NUM>.

In the context of the present invention, the compensation voltage Vc between the first and the second end of the voltage generator <NUM> is defined as the potential difference obtained by subtracting the electrical potential of the first end of the voltage generator <NUM> from the electrical potential of its second end.

According to one aspect of the invention, the compensation circuit <NUM> may comprise a capacitive two-terminal network <NUM>, preferably connected in series with the voltage generator <NUM>. The capacitive two-terminal network <NUM> is preferably formed by a capacitor.

Preferably, the capacitive two-terminal network <NUM> has a predefined and/or preset capacitance CC. Preferably, the capacitance CC of the capacitive two-terminal network <NUM> is such as to create a compensation current IC having an r. value (essentially) equal to the r. value of the capacitive leakage current ICD.

Preferably, the capacitance CC of the capacitive two-terminal network <NUM> is essentially equal to the equivalent parasitic capacitance of the circuit <NUM>.

Preferably, the capacitive two-terminal network (<NUM>) is of the controllable capacitance type.

In other words, the capacitance CC of the capacitive two-terminal network <NUM> is a parameter that can be modified by an operator using adjustment means such as switches, selectors and/or software configurations of the compensation device <NUM>. The input means <NUM> of the compensation device <NUM> may comprise the aforesaid adjustment means.

This enables an operator to modify the value of the capacitance CC of the capacitive two-terminal network <NUM> so as to vary the r. value of the compensation current IC generated by the compensation circuit <NUM> without modifying the compensation voltage Vc generated by the voltage generator <NUM>.

With reference to <FIG>, the voltage generator <NUM> is connected via its first end to the first terminal <NUM>, and via its second end to a first end of the capacitive two-terminal network <NUM>. The capacitive two-terminal network <NUM> is connected via its second end to the second terminal <NUM>.

In an alternative embodiment of the invention, the capacitive two-terminal network <NUM> may be connected via its first end to the first terminal <NUM>, and via its second end to the first end of the voltage generator <NUM>, the latter being connected via its second end to the second terminal <NUM>.

Preferably, the voltage generator <NUM> is configured to generate the compensation voltage Vc in such a way that it is substantially proportional, but of opposite sign, to the voltage between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>, in order to cause the compensation current IC to flow through the capacitive two-terminal network <NUM>.

Preferably, the voltage generator <NUM> is a dependent voltage generator which generates the compensation voltage Vc on the basis of the voltage present between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>.

Preferably, the absolute value of the ratio between the compensation voltage Vc and the voltage between the phase conductor <NUM> and the neutral conductor <NUM> is equal to <NUM>. Preferably, the compensation voltage Vc is of opposite sign to the voltage between the phase conductor <NUM> and the neutral conductor <NUM>.

In other words, a positive value of the voltage present between the phase conductor <NUM> and the neutral conductor <NUM> at a given instant of time corresponds to a negative value of the compensation voltage Vc, and vice versa.

In one embodiment of the invention, the compensation voltage Vc is opposed to the voltage between the phase conductor <NUM> and the neutral conductor <NUM> for at least <NUM>% of the period of the latter voltage.

In a preferred embodiment of the invention, the amplitude and frequency of the compensation voltage Vc are the same as the (nominal) voltage applied between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>.

Preferably, the values of the compensation voltage Vc have the same variation in time, but of opposite sign, as the voltage present between the phase conductor <NUM> and the neutral conductor <NUM>, thus also replicating any excess voltages or other transient phenomena that may affect the circuit <NUM>.

In other words, the voltage generator <NUM> may be configured to generate a compensation voltage Vc in such a way that it is substantially proportional to the voltage between the third terminal <NUM> and the first terminal <NUM>, in order to cause the compensation current IC to flow through the capacitive two-terminal network <NUM>. The voltage generator <NUM> may be provided with the third terminal <NUM> so as to generate the compensation voltage Vc on the basis of the voltage present between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>, that is on the basis of the voltage between the third terminal <NUM> and the first terminal <NUM>.

In a further embodiment of the invention, the compensation circuit <NUM> comprises, in addition to the third terminal <NUM>, a fourth terminal that can be connected to the protective conductor of the circuit <NUM>. In this case, the compensation circuit <NUM> is configured to use the voltage present between the third terminal <NUM> and the fourth terminal to generate the compensation current IC.

Preferably, the third terminal <NUM> and the fourth terminal are connected, respectively, to the phase conductor <NUM> and to the protective conductor, and the voltage present between these terminals represents, and in particular is proportional to, the voltage between the phase conductor <NUM> and the protective conductor of the circuit <NUM>.

In this embodiment, the voltage generator <NUM> is preferably configured to generate the compensation voltage Vc in such a way that it is substantially proportional, but of opposite sign, to the voltage between the phase conductor <NUM> and the protective conductor, in order to cause the compensation current IC to flow through the capacitive two-terminal network <NUM>.

Preferably, the absolute value of the ratio between the compensation voltage Vc and the voltage between the phase conductor <NUM> and the protective conductor is equal to <NUM>.

<FIG> shows a preferred embodiment of the invention.

In this embodiment, the voltage generator <NUM> is formed by a transformer whose primary winding <NUM> is connected via its first end to the third terminal <NUM> and via its second end to the neutral conductor <NUM> of the circuit <NUM>. In particular, the second end of the primary winding <NUM> is connected to the neutral conductor <NUM> via a terminal <NUM>' of the compensation circuit <NUM> which is separate from the first terminal <NUM>.

The secondary winding <NUM> of the aforesaid transformer is connected via its first end to the first terminal <NUM>, and via its second end to the first end of the capacitive two-terminal network <NUM>.

Preferably, the transformer is a <NUM>:<NUM> transformer, and more preferably it has a wide-band frequency response.

Advantageously, the embodiment of the invention shown in <FIG> is not provided with active components, and therefore no special power supplies are required to energize the device <NUM>.

<FIG> shows a further embodiment of the invention.

In this embodiment, the voltage generator <NUM> is formed by a four-quadrant inverting AC/AC converter. In particular, the voltage generator <NUM> is a switched-capacitor voltage inverter.

The voltage generator <NUM> comprises a first capacitor C1 whose first end is connected to the first terminal <NUM> of the compensation circuit <NUM> and whose second end is connected to the first end of the capacitive two-terminal network <NUM>. The voltage generator <NUM> also comprises a second capacitor C2 whose first end is connected to the third terminal <NUM> through a first switch S1 and whose second end is connected to the capacitive two-terminal network <NUM> through a second switch S2.

The first end of the first capacitor C1 is also connected to the first end of the second capacitor C2 through a third switch S3 and to the second end of the second capacitor C2 through a fourth switch S4. The second end of the first capacitor C1 is also connected to the second end of the second capacitor C2 through the second switch S2.

The device <NUM> further comprises a control unit <NUM>, such as a microcontroller, configured to control the actuation of the switches S1 - S4 which are alternately opened and closed at a predetermined frequency fS. Preferably, the actuation frequency fS of the switches S1 - S4 is within the range from <NUM> to <NUM>.

Preferably, the actuation sequence of the switches S1 - S4 provides for the cyclic alternation of a first and a second period T1, T2, both having a duration of <NUM>/(2fS).

In the first period T1, switches S1 and S4 are closed and switches S2 and S3 are open, so that the first capacitor C1 is charged at the voltage present between the phase conductor <NUM> and the neutral conductor <NUM> of the circuit <NUM>. In the second period T2, switches S1 and S4 are open and switches S2 and S3 are closed, so that the first capacitor C1 is electrically connected to the second capacitor C2, thereby transferring to the latter at least part of the charge accumulated in the first period T1.

Thus, at a sufficiently high value of the frequency fS (typically <NUM>), a compensation voltage Vc is generated between the first and second ends of the second capacitor C2, this voltage being opposed, and in particular being in phase opposition, to that present between the phase conductor <NUM> and the neutral conductor <NUM>, thereby causing the alternating flow of the compensation current IC from and towards earth through the capacitive two-terminal network <NUM>.

This embodiment of the invention advantageously enables a compensation circuit <NUM> to be constructed with smaller dimensions, resulting in a less bulky compensation device <NUM>.

Furthermore, the compensation device <NUM> of <FIG> is found to be particularly suitable for generating a compensation current IC in perfect phase opposition to the permanent capacitive leakage current ICP, and also has a sufficiently wide response band to provide correct compensation of transient capacitive leakage currents, particularly those of a pulsed type.

To prevent the action of resetting a residual current device <NUM> from causing untimely tripping of the circuit breaker, the compensation device <NUM> may comprise a rapid AC/DC power supply <NUM> for generating a DC output voltage capable of energizing the control unit <NUM>, in which the settling time of the aforesaid output voltage is less than ten milliseconds, or more preferably less than five milliseconds.

<FIG> shows an exemplary embodiment of the rapid AC/DC power supply <NUM>. The rapid AC/DC power supply <NUM> comprises a rectifier device <NUM> whose output is connected to a DC/DC converter <NUM>. A capacitor C3 is connected to the output line of the rectifier device <NUM> upstream of the DC/DC converter. The rapid AC/DC power supply is also provided with a switch device <NUM> such as a relay, positioned so as to short-circuit the impedance <NUM> in series with the input of the rapid AC/DC power supply <NUM> when the switch device <NUM> is closed.

The impedance <NUM> in series with the input may be used to limit the current drawn by the rapid AC/DC power supply <NUM> from an electrical network when its input is connected to the latter.

The actuation of the switch device <NUM> is controlled on the basis of the voltage present at the ends of the capacitor C3.

The switch device <NUM> is normally closed when the rapid AC/DC power supply <NUM> is not connected to an electrical network, or is not energized by such an electrical network, thus establishing a low impedance at the input of the rectifier device <NUM>.

The rapid AC/DC power supply may also be provided with a protection system (PTC) capable of opening the electrical circuit of the power supply <NUM> if the switch device <NUM> does not operate correctly or is not actuated within the specified time interval.

When the rapid AC/DC power supply <NUM> is energized by an electrical network and the switch device <NUM> is closed, the capacitor C3 is charged at the output voltage of the rectifier device <NUM> in a relatively short time (less than a millisecond), thus ensuring the rapid activation of the control unit <NUM> and consequently the rapid activation of the compensation device <NUM> connected downstream of the rapid AC/DC power supply <NUM>.

As soon as the voltage at the ends of the capacitor C3 reaches a predetermined value, the switch device <NUM> is opened, connecting the impedance <NUM> in series with the upstream input of the rectifier device <NUM>.

Claim 1:
A compensation device suitable for compensating a capacitive leakage current of a circuit of a single-phase electrical system, the circuit (<NUM>) comprising:
• a phase conductor (<NUM>) and a neutral conductor (<NUM>) connected, respectively, to a first conductor (<NUM>) and to a second conductor (<NUM>) of a single-phase electrical line (<NUM>), the second conductor (<NUM>) of the single-phase electrical line (<NUM>) being connected to earth, and
• one or more loads (<NUM>) which can be energized with alternating current from the single-phase electrical line (<NUM>) via the phase and neutral conductors (<NUM>, <NUM>), the phase and neutral conductors (<NUM>, <NUM>) and the loads (<NUM>) able to generate a capacitive leakage current (ICD) towards earth,
the compensation device (<NUM>) comprising a compensation circuit (<NUM>) provided with a first and a second terminal (<NUM>,<NUM>) and being characterized in that the compensation circuit (<NUM>) is:
• arranged to be connected to the neutral conductor (<NUM>) via the first terminal (<NUM>) and to an earthing system (<NUM>) via the second terminal (<NUM>), and
• configured to generate a compensation current (IC) in such a way that it flows alternately from the neutral conductor (<NUM>) to earth and vice versa through the earthing system (<NUM>) when the first and second terminals (<NUM>, <NUM>) are connected, respectively, to the neutral conductor (<NUM>) and to the earthing system (<NUM>), the compensation current (IC) having direction which is opposite that of the capacitive leakage current (ICD) and intensity such that the sum of the compensation current (IC) and the capacitive leakage current (ICD) has a smaller value than the value of the capacitive leakage current (ICD),
wherein the circuit (<NUM>) comprises a residual current device (<NUM>) whose input is connected to the single-phase electrical line (<NUM>) and whose output is connected to the phase and neutral conductors (<NUM>, <NUM>), the compensation device (<NUM>) being connected to the circuit (<NUM>) downstream of the residual current device (<NUM>) with respect to the single-phase electrical line (<NUM>).