Main current measurement device for an electrical installation, measurement method, and protection method using such a device

Abstract

Main current measurement device of an electrical installation, measurement method and protection method using such a device. The invention relates to a main current measurement device (1) of an electrical installation comprising N conductors (3). The device comprises a closed magnetic circuit (5), at least N-1 main current measurement windings (11), a support structure (6), means for measuring a voltage (V11) across the main current measurement windings (11) and a calculation unit (15).Each main current measuring coil comprises two windings in series (111, 112), each wound around a portion of the magnetic circuit (5), not equidistant from at least one of the conductors (3), and with opposite winding directions from one winding (111, 112) to the other, such that a uniform magnetic field in the magnetic circuit (5) generates a voltage that cancels out across the terminals of the main current measuring coil (11). Figure for the abbreviation: Figure 1.

Description

Title of the invention: Device for measuring main currents in an electrical installation, method of measurement and method of protection using such a device

[0001] The present invention relates to a device for measuring the main currents of an electrical installation. It also relates to a method for measuring the main currents of an electrical installation using such a device. It also relates to a method for protecting an electrical installation using such a device.

[0002] It is useful to know the currents flowing in each of the phase or neutral wires of an electrical installation, called main currents, for indication or protection purposes. For this purpose, it is known to use sensors of various technologies, such as CT sensors, resistive shunts, Rogowski coils, or Hall effect sensors.

[0003] However, measuring main currents using these methods requires installing several sensors, generally one per conductor. Furthermore, these sensors are usually added to a differential current measurement sensor. This multiplicity of sensors in the installation results in significant bulk and cost.

[0004] The aim of the invention is therefore to propose a device for measuring the main currents of an electrical installation which allows the total number of sensors in the installation to be reduced, in order to obtain a saving of space, a saving on the cost of the sensors and on the cost of the assemblies.

[0005] To this end, the invention relates to a device for measuring the main currents of an electrical installation comprising a number N of conductors carrying a main current I, comprising:

[0006] - a closed magnetic circuit, composed of a ferromagnetic material and configured to surround the drivers;

[0007] - at least Nl main current measuring windings, each winding of measurement of the main current comprising two windings in series which:

[0008] i. are each wound around a part of the closed magnetic circuit,

[0009] ii. are not equidistant from at least one of the conductors, so that the main current 7 flowing in said at least one conductor generates a different magnetic flux at each of the two windings, and

[0010] iii. have an opposite winding direction from one winding to the other, so that a uniform magnetic field in the magnetic circuit generates a voltage which cancels out across the terminals of the main current measuring winding;

[0011] - a retaining structure configured to retain the conductors in a given arrangement where the conductors are not coaxial;

[0012] - means for measuring a voltage across the terminals of the Nl measuring windings of the main current; and

[0013] - a calculation unit, connected to the means for measuring the voltage.

[0014] Thanks to the invention, a single sensor is required to measure the currents flowing in several conductors simultaneously. Indeed, since the conductors are not coaxial, the currents flowing in different conductors will have different influences on the resulting magnetic field at a given point in the magnetic circuit. Thus, since the main current measurement coils are located around a portion of the magnetic circuit, the voltage generated across a main current measurement coil depends on the main currents. Therefore, by measuring the voltages across the primary current coils, and using knowledge of the geometry or a calibration procedure, it is possible to obtain as many equations for the main currents as there are primary current measurement coils.Having at least Nl equations thus obtained, possibly supplemented by an additional equation resulting from the vector equality of the main currents of an installation, it is possible to deduce the value of each main current from the single main current measurement device. This device eliminates the need for the usual multiplicity of main current measurement sensors, and therefore saves space and costs by reducing the total number of sensors in the installation.

[0015] According to other advantageous aspects of the invention, the main current measurement device comprises one or more of the following features, taken individually or in any technically possible combination:

[0016] - the magnetic circuit is symmetrical in shape, that is to say, it comprises at least one axis of symmetry and / or a center of symmetry;

[0017] - at least one axis of symmetry is also an axis of symmetry of the structure of maintenance;

[0018] - the two windings of each main current measuring winding are arranged symmetrically with respect to the center of symmetry of the magnetic circuit or with respect to at least one axis of symmetry;

[0019] - there are 2 main conductors, one of the conductors being a wire of phase and the other being a neutral wire of a single-phase electrical installation or another phase wire of a two-phase electrical installation;

[0020] - there are 3 conductors, two of the three conductors being wires of phase and the third conductor being a third phase wire or a neutral wire of an electrical installation;

[0021] - there are 4 conductors, three of the conductors being phase wires and the fourth being a neutral wire of an electrical installation;

[0022] - the device includes a differential current measuring coil, wound regularly around the closed magnetic circuit, and a means for measuring a current flowing in the differential current measuring coil, connected to the calculation unit or another calculation unit.

[0023] The invention also relates to a method for measuring the main currents of an electrical installation, implemented by the calculation unit of a main current measuring device according to the foregoing and comprising steps consisting of:

[0024] - receive voltage values ​​across each measuring winding of the main current, measured by voltage measuring means;

[0025] - convert the voltage values ​​across each measuring winding of the main current in main current values, corresponding to the currents flowing in the main conductors; then

[0026] - to restore the main current values ​​in analog or digital form.

[0027] The invention also relates to a method for protecting an electrical installation, the electrical installation having a leakage current defined as the difference between the sum of the main currents entering the electrical installation and the sum of the main currents leaving the electrical installation, the method being implemented by the calculation unit of a main current measuring device according to the invention, comprising steps consisting of:

[0028] - receiving a value of the current flowing in the current measuring coil differential, measured by the current measuring device;

[0029] - deduce from this, using a proportionality coefficient obtained by calibration First, the leakage current value; then

[0030] - control a switch to interrupt a power supply to the electrical installation if and only if the leakage current value is greater than a predetermined threshold value.

[0031] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0032] [Fig-1] [Fig.1] is an assembly diagram of a current measurement device principal components according to the invention, in the case of a two-conductor installation according to a first embodiment of the invention,

[0033] [Fig.2] [Fig.2] is a diagram of part of a current measurement device principal components according to the invention, in the case of a two-conductor installation according to a second embodiment of the invention,

[0034] [Fig.3] [Fig.3] is a diagram of part of a current measurement device principal components according to the invention, in the case of a three-conductor installation,

[0035] [Fig.4] [Fig.4] is a diagram of part of a current measurement device principal according to the invention, in the case of a four-pole installation.

[0036] The main current measuring device 1 shown in Figure 1 is integrated into an input of an electrical installation, where circuit breakers and current measuring sensors are usually located. For ease of understanding, we will initially limit ourselves to the description of a single-phase electrical installation. The installation is then supplied by two conducting wires, called conductors 3, in which main currents 7 flow. The first conductor 3A is a phase wire, through which a first main current Ja enters the electrical installation. The second conductor 3B is a neutral wire, through which a second main current Jb leaves the electrical installation. The conductors 3 supply a set of electrical devices belonging to the electrical installation.

[0037] In the absence of an anomaly, the main currents M and TB are equal in absolute value. In the event of an anomaly in the electrical installation, there is a leakage current Jy in the electrical installation, also called a differential current, such that ΔA = ΔB + Jf. The leakage current Jy is a potential source of danger for users of the electrical installation or for the aforementioned electrical appliances. The value of the leakage current Jy is generally small compared to the values ​​of the main currents Ja and IB.

[0038] The main current measuring device 1 is designed to measure the values ​​of the main currents Ta and / B, for indication or protection purposes. In particular, measuring the main currents JA and / B is useful for monitoring the electrical consumption of the installation.

[0039] Advantageously, and in the example of Figure 1, the main current measuring device 1 also has the function of measuring the leakage current JJ. This measurement is useful for protecting the electrical installation by interrupting the power supply in the event of the presence of a leakage current JJ, according to the known principle of a residual current circuit breaker.

[0040] For this purpose, the main current measuring device 1 comprises a magnetic circuit 5, a holding structure 6, a current measuring coil differential 7, a current measuring means 9, a main current measuring coil 11, a voltage measuring means 13 and a calculation unit 15.

[0041] The magnetic circuit 5 surrounds the conductors 3. In other words, the conductors 3 pass through the magnetic circuit 5. The magnetic circuit 5 extends in a plane (x,y) shown in Figures 1 to 4. This magnetic circuit is closed and made of a ferromagnetic material, so that a magnetic flux F can flow through it. The magnetic circuit 5 is advantageously symmetrical, that is, it includes at least one axis of symmetry A and / or a center of symmetry C5. The axis of symmetry A is defined as the intersection of the plane (x,y) with a plane of symmetry of the magnetic circuit 5, preferably perpendicular to the plane (x,y). Thus, the axis of symmetry A is perpendicular to the z-axis, therefore to the conductors 3, and is contained in the (x,y) plane, i.e. in the plane of the magnetic circuit 5. The magnetic circuit 5 shown in [Fig.1] is circular with center C5, which optimizes the compactness and quantity of material of the device 1.

[0042] In a non-represented variant of the invention, the magnetic circuit 5 may be oblong, rectangular or any other shape.

[0043] Preferably, the conductors 3 are held by the holding structure 6 in a position where they are perpendicular to the magnetic circuit 5. In other words, the conductors 3 extend parallel to an axis z normal to the plane (x,y).

[0044] The retaining structure 6 is attached to the magnetic circuit 5 and holds the conductors 3 in a given arrangement in which they are not coaxial. For example, the retaining structure may be a bracket made of insulating material through which the conductors 3 pass and which is positioned in the vicinity of the magnetic circuit 5, without necessarily being coplanar with this circuit.

[0045] Advantageously, the aforementioned axis of symmetry A is also an axis of symmetry of the retaining structure 6. In other words, the assembly consisting of the retaining structure 6 and the magnetic circuit 5 defines at least one axis of symmetry A.

[0046] The differential current measuring coil 7 is, in a known manner, wound regularly around the magnetic circuit 5. In operation, the main currents / [ and / ^ flowing in the conductors 3A and 3B generate magnetic fluxes FA and FB in the magnetic circuit 5. Since the main currents JA^JB are in opposite directions, the magnetic fluxes FA and FB are in opposite directions.

[0047] In the absence of anomaly, the main currents j^et Jb being of the same value and opposite direction, the same is true for the magnetic fluxes FA and FB, which then cancel each other out in the magnetic circuit 5 and are not perceptible by the differential current winding 7 by balance and symmetry.

[0048] In the event of an anomaly, the principal currents Ja and Jb no longer being of the same value, there exists in the magnetic circuit 5 a resulting differential magnetic flux Ff The difference between the magnetic fluxes FA and FB, and therefore the difference between the main currents Ta and IB, is the leakage current ff. This differential magnetic flux Ff generates a resultant current 77 in the differential current winding 7. In other words, the resultant current 77 in the differential current winding 7 is proportional to the leakage current jf and independent of the main currents Ja and TB. The differential current measuring winding 7 forms a circuit in series with the current measuring means 9. The current measuring means 9 is typically an ammeter and has a very low internal ammeter resistance R9, for example, less than 100Ω. Thus, the differential current measuring winding 7 is practically short-circuited, so that the current transformer operation of the differential current measuring winding 7 is only very slightly or not at all affected by the current measuring means 9.

[0049] The current measuring means 9 thus measures the current 77 flowing in the differential current measuring coil 7. According to the above, the current measuring means 9 therefore measures a current proportional to the leakage current Jy and independent of the main currents IA and TB-

[0050] The main current measuring windings 11 are at least Nl in number, where N is the number of conductors 3. In the embodiment considered in [Fig. 1], where N is equal to 2, the main current measuring device 1 comprises a single main current measuring winding IL

[0051] The main current measuring winding 11 comprises two windings 111 and 112. As shown in Figure 1, the two windings 111 and 112 are connected in series and each is wound around a portion of the magnetic circuit 5. The two windings 111 and 112 are not equidistant from either of the conductors 3A and 3B; that is, there is at least one conductor 3A or 3B such that the distance from the first winding 111 to this conductor 3A or 3B is different from the distance from the second winding 112 to this conductor 3A or 3B. Thus, the main current TA or T§ flowing in this conductor 3A or 3B generates a different magnetic flux at each of the two windings 111 and 112. This is possible thanks to the aforementioned arrangement, ensured by the support structure 6, an arrangement in which the conductors 3 are not coaxial. In the example of [Fig.1], the two windings 111 and 112 are not equidistant from conductor 3A, nor are they equidistant from conductor 3B.

[0052] Thus, the magnetic fluxes FA and FB generated by the main currents Ja and ÏB flowing in the conductors 3A and 3B have a different influence on a resulting magnetic flux at a winding 111 or 112. In particular, in the arrangement shown in Figure 1, the first winding 111 is closer to the primary conductor 3 A than the second winding 112. Consequently, the main current JX has a greater contribution to the resulting magnetic flux at the first winding 111 than to the resulting magnetic flux at the second winding 112. Similarly, the main current Jb has a greater contribution to the resulting magnetic flux at the second winding 112 than to the resulting magnetic flux at the first winding 111.

[0053] The oriented angle T1 is defined between a line passing through the centers of conductors 3A and 3B and a line passing through the center of symmetry C5 of the magnetic circuit 5 and through the position of the first winding 111 on the magnetic circuit 5. Similarly, the oriented angle T2 is defined between the line passing through the centers of conductors 3A and 3B and a line passing through the center of symmetry C5 of the magnetic circuit 5 and through the position of the second winding 112.

[0054] In the first embodiment shown in [Fig.1], the two windings 111 and 112 of each main current measuring winding 11 are arranged symmetrically with respect to the axis of symmetry A. In other words, the angles T1 and T2 are of equal absolute value and opposite direction.

[0055] In the second embodiment of the invention shown in [Fig.2], the two windings 111 and 112 of each main current measuring winding 11 are arranged symmetrically with respect to the center C5 of the magnetic circuit 5. In other words, the angles T1 and T2 are equal.

[0056] This symmetry is advantageous for simplification purposes but is not a strictly essential feature of the invention. Indeed, for any number of conductors 3 and any geometry of the magnetic circuit 5, a numerical simulation can define an optimal position for the two windings 111 and 112 of the main current measuring coil 11. However, the optimal positioning of the two windings 111 and 112 is facilitated by the presence of the axis of symmetry A and / or the center of symmetry C5. The two windings 111 and 112 are then optimally positioned by being themselves symmetrical with respect to the axis of symmetry A or with respect to the center of symmetry C5.

[0057] In both embodiments of Figures 1 and 2, the two windings 111 and 112 also have opposite winding directions. Thus, the differential magnetic flux Ff, uniform in the magnetic circuit 5, generates a resultant voltage in the opposite direction across each of the two windings 111 and 112. Since these two windings are in series, these contributions cancel each other out, so that the resultant voltage Vil across the main current measuring winding 11 is independent of the differential flux Ff, and therefore of the leakage current Jy.

[0058] For the same reason, the resulting magnetic flux at the first winding 111, which is mainly due to the magnetic flux FA generated by the main current 7X, and the resulting magnetic flux at the second winding 112, which is mainly due to the magnetic flux FB generated by the main current TB and in the opposite direction to the magnetic flux FA, generate voltages in windings 111 and 112 that add together without canceling each other out. Thus, the resulting voltage Vil across the main current measuring winding 11 depends on the main currents M and / gen and is independent of the leakage current Tf.

[0059] As explained above, the presence of the two series windings 111 and 112 with opposite winding directions makes the measurement of the main currents Ta and IB independent of the leakage current Jy. This characteristic is essential because the leakage current Jy, although small compared to the main currents TA and IB, generates a differential magnetic flux Ff in the magnetic circuit 5, which is predominant compared to the magnetic fluxes FA and FB.

[0060] The main current measuring coil 11 forms a circuit in series with the voltage measuring means 13. The voltage measuring means 13 is typically a voltmeter and has a high internal voltmeter resistance R13, for example greater than 1 MΩ. Thus, the measurement of the main currents does not influence, or only negligibly influences, the measurement of the differential current Jy.

[0061] The voltage measuring means 13 thus measures the resulting voltage Vil across the terminals of the main current measuring coil 11. According to the above, the voltage measuring means 13 therefore measures a voltage dependent on the main currents TA and TB and independent of the leakage current Jy.

[0062] The calculation unit 15 receives the current measurement Tl provided by the current measuring means 9 and the voltage measurement Vil provided by the voltage measuring means 13, in order to deduce a differential current value / y and the main current values ​​Ta and TB-

[0063] As explained previously, the value of the TT current is proportional to the value of the leakage current Jy. Thanks to a preliminary calibration step, the calculation unit 15 therefore simply converts the measurement of the TT current into a differential current value Jy. The calculation unit 15 outputs the differential current value Jy in analog or digital form or uses it to control whether or not the power supply to the electrical installation is interrupted.

[0064] As explained previously, the voltage Vil depends on the values ​​of the main currents TA and IB. Knowing the geometry of the main current measuring device 1, and in particular the arrangement of the conductors 3 fixed by the device Using a maintenance step 6, or alternatively a calibration step, the calculation unit 15 converts the voltage measurement V11 into an equation for the main currents J1 and Jb. Since the leakage current Jy is small compared to the values ​​of the main currents Ja and Jb, we can, for this measurement, approximate that the currents M and Jb are equal. This equality provides a second equation for the main currents M and Jb. Alternatively, not shown, the second equation for the main currents Ja and Jb can be derived from similar reasoning using an additional main current measurement coil. From the two equations for the main currents Ja and JB, the calculation unit 15 determines the values ​​of each main current Ia and Jb and outputs these values ​​in analog or digital form.

[0065] In an alternative not shown, the main current measurement device 1 comprises two separate calculation units, one of the two calculation units receiving the current measurement / 7 and performing the conversion of the current measurement Ï7 and the other of the two calculation units receiving the voltage measurement VI1 and performing the conversion of the voltage measurement Vil.

[0066] Alternatively, the electrical installation is a two-phase electrical installation and the two conductors 3A and 3B are two phase wires.

[0067] Figures 3 and 4 represent a generalization of the above example to the cases of an electrical installation with three conductors and four conductors, respectively. In the embodiments of Figures 3 and 4, the elements analogous to those of the first embodiment bear the same reference numerals. If a reference numeral is mentioned later in the description but not shown in either of Figures 3 and 4, or if it is shown in either of these figures but not mentioned later in the description, it corresponds to the element bearing the same reference numeral in the first embodiment. The following primarily describes the differences between the example of the single-phase installation and the generalization to three conductors and four-pole installations.

[0068] In the case of a three-conductor installation shown in Figure 3, the main conductors are labeled 3A, 3B, and 3C, and the main currents flowing in these conductors 3A, 3B, and 3C are labeled Ja, Jb, and Jq, respectively. For example, the electrical installation is three-phase, and conductors 3A, 3B, and 3C are then three phase wires. Alternatively, two of the three conductors, 3A and 3B, are phase wires, and the third conductor, 3C, is a neutral wire.

[0069] The main current measuring windings 11 are then at least two in number. In [Fig. 3], three main current measuring windings 1IA, 1IB and 1IC are shown. As can be seen in [Fig. 3], the two windings 111 and 112 of each main current measuring winding 11 are advantageously symmetrical. between them with respect to the center of symmetry C5 of the magnetic circuit 5, as in the embodiment of [Fig.2].

[0070] The two windings of the first main current measuring winding 11A are marked 111A and 112A, The two windings of the second main current measuring winding 1 IB are marked 11 IB and 112B and the two windings of the third main current measuring winding 1 IC are marked 11 IC and 112C.

[0071] In this case, three equations with three unknowns / X 1B and I are obtained and solved by the computing unit 15, providing the three main current values ​​zX IB and [C

[0072] In the case of a four-pole installation, there are four conductors: three phase wires 3A, 3B, and 3C and one neutral wire 3D, in which the respective main currents Ci- IB, IC, and ID- flow. In the example illustrated in Figure 4, device 1 is then similar to the three-conductor case, and the fourth equation for the main currents comes from the approximation JÂ + ÏB + ÏC = ÏD-

[0073] The windings 11 IA, 112A, 11 IB, 112B, 11 IC and 112C of the main current measuring windings 11 A, 1 IB and 1 IC are identified as in the embodiment of [Fig.3].

[0074] A voltage measuring means (not shown), of the type of voltage measuring means 13, is connected in series with each main current measuring winding 1 IA, 1 IB and 1 IC and allows a voltage of the type VIL to be measured

[0075] The implementation of a method for measuring main currents of an electrical installation using a main current measuring device 1 conforming to the above, after a possible calibration operation, is described in the remainder of the description.

[0076] In operation, the main currents Z flowing in the N conductors 3 generate magnetic fluxes F in the magnetic circuit 5, which magnetic fluxes in turn generate a resulting current Z7 in the differential current measuring winding 7 and voltages VI1 and equivalent across the terminals of the main current measuring windings 11, 1 IA, 1 IB and 1 IC.

[0077] As explained previously, due to the geometry of the main current measuring device 1, the resulting current Z7 in the differential current measuring coil 7 is proportional to the leakage current ÿy while being independent of the main currents Z.

[0078] Similarly, the resulting voltages VI1 and equivalent across the terminals of the main current measuring windings 11,11 A, 1 IB and 1 IC, are dependent on the main currents Z while being independent of the leakage current jy.

[0079] The method for measuring the main currents, implemented by the calculation unit 15, then consists of: - receive voltage values ​​Vil across the terminals of each main current measuring winding 11, measured by the voltage measuring means 13; - deduce, using knowledge of the geometry of the main current measurement device 1 or of the prior calibration, the at least Nl equations on the main currents I; - possibly, complete with an equation derived from the vector equality approximation of the main currents of an electrical installation; - solve the system of N equations where the N unknowns are the N main currents 7; - to display the main current values ​​7 in analog or digital form.

[0080] Advantageously, the calculation unit 15 implements in parallel the installation protection method which consists of: - receive a value 17 of the current 77 flowing in the differential current measuring coil 7, measured by the current measuring means 9; - deduce, using a proportionality coefficient obtained by prior calibration, the value of the leakage current Jy; - control a switch to interrupt the power supply to the electrical installation if and only if the value of the leakage current jy is greater than a predetermined threshold value.

[0081] Thus, the main currents 7 of the conductors 3 of the electrical installation are measured by means of the single main current measuring device 1, while ensuring the protection function of a differential circuit breaker.

[0082] Any feature described above for one embodiment or variant can also be implemented in the other embodiments or variants described above, as far as technically possible.

Claims

1.

2.

3. Demands Main current measurement device (1) of an electrical installation comprising a number N of conductors (3) carrying a main current / , characterized in that the device comprises: • a closed magnetic circuit (5), composed of a ferromagnetic material and configured to surround the conductors (3); • at least Nl main current measuring windings (11), each main current measuring winding comprising two windings in series (111, 112) which: i. are each wound around a portion of the closed magnetic circuit (5), ii. are not equidistant from at least one of the conductors (3), such that the principal current I flowing in said at least one conductor generates a different magnetic flux at each of the two windings (111,112), and iii. have an opposite winding direction from one winding (111, 112) to the other, so that a uniform magnetic field in the magnetic circuit (5) generates a voltage which cancels out across the terminals of the main current measuring winding (11); • a holding structure (6) configured to hold the conductors (3) in a given arrangement where the conductors (3) are not coaxial; • means for measuring (13) a voltage (V11) across the terminals of the main current measuring windings (11); and • a calculation unit (15), connected to the means of measuring (13) the voltage (Vil). Device (1) according to claim 1, wherein the magnetic circuit (5) is symmetrical in shape, i.e., comprises at least one axis of symmetry (A) and / or a center of symmetry (C5). Device (1) according to claim 2, wherein at least one axis of symmetry (A) is also an axis of symmetry of the retaining structure (6).

4. Device (1) according to claim 2 or 3, wherein the two windings (111, 112) of each main current measuring winding (11) are arranged symmetrically with respect to the center of symmetry (C5) of the magnetic circuit (5) or with respect to at least one axis of symmetry (A).

5. Device (1) according to claim 4, wherein the main conductors (3) are of 2, one of the conductors being a phase wire (3A) and the other being a neutral wire (3B) of a single-phase electrical installation or another phase wire (3B) of a two-phase electrical installation.

6. Device (1) according to claim 4, wherein the conductors (3) are 3 in number, two of the three conductors (3A, 3B) being phase wires and the third conductor (3C) being a third phase wire or a neutral wire of an electrical installation.

7. Device (1) according to claim 4, wherein the conductors (3) are of the number 4, three of the conductors being phase wires (3A, 3B, 3C) and the fourth being a neutral wire (3D) of an electrical installation.

8. Device (1) according to any one of the preceding claims, comprising: • a differential current measuring coil (7), wound regularly around the closed magnetic circuit (5), and • a means for measuring a current ( / 7) flowing in the differential current measuring coil (7), connected to the calculation unit (15) or to another calculation unit.

9. A method for measuring the main currents of an electrical installation, implemented by the calculation unit (15) of a main current measuring device (1) according to any one of the preceding claims, comprising steps of: • receiving voltage values ​​(Vil) across each main current measuring coil (11), measured by the voltage measuring means (13); • converting the voltage values ​​(Vil) across each main current measuring coil (11) into main current values, corresponding to the currents flowing in the main conductors (3); then • to display the main current values ​​in analog or digital form.

10. A method for protecting an electrical installation, the electrical installation having a leakage current (Jy) defined as the difference between the sum of the main currents entering the electrical installation and the sum of the main currents leaving the electrical installation, the method being implemented by the calculation unit (15) of a main current measuring device (1) according to claim 8, comprising steps of: • receiving a value (17) of the current (Jy) flowing in the differential current measuring coil (7), measured by the current measuring means (9); • deducing therefrom, by means of a proportionality coefficient obtained by prior calibration, the value of the leakage current (Jy); and then • controlling a switch to interrupt the supply to the electrical installation if and only if the value of the leakage current (Jy) is greater than a predetermined threshold value.

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