Detection of neutral line loss

Abstract

A method for detecting the interruption of the connection of the neutral line (6) of a three-phase electric power network, the method being implemented in a processing unit (7A) of an item of electrical equipment (7) connected to the electric power network (1) and comprising the following steps: - acquisition, at a time T, of a first phase voltage (V1), a second phase voltage (V2) and a third phase voltage (V3) measured by a voltage sensor (7D) of the electrical equipment (7); evaluation of a first quantity representative of the ratio of the maximum voltage to the minimum voltage from the first, second and third phase voltages; - if the first quantity is greater than a predetermined threshold: o evaluation of a second quantity based on the first phase voltage, the second phase voltage and the third phase voltage; o detection of the interruption of the neutral line (6) at the time T when the second quantity satisfies a predetermined reference criterion.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrical power distribution networks and equipment connected to said networks. BACKGROUND

[0002] An electrical power distribution network is used to transmit electrical power from a power generation unit to one or more connected electrical installations. The electrical power is usually transmitted in three phases and the power network is then composed of three phase conductors and a neutral conductor. The power network is usually also equipped with a plurality of electricity meters for measuring the electrical power consumed by the connected electrical installations.

[0003] In a three-phase power network, the interruption of the neutral connection can occur upstream of one or more meters. Such an interruption is the responsibility of the energy supplier in charge of the network and can cause major problems at the connected electrical installations. Indeed, depending on the load impedance of the connected electrical installations (downstream of the breakpoint of the neutral), a significant imbalance of the phase voltages carried by the three phase conductors can occur. Consequently, high voltages can exist at the connected electrical installations, which can damage said installations.

[0004] It is therefore important to be able to reliably, simply and quickly detect a sudden interruption of the neutral connection in a three-phase electrical power distribution network. This allows preventive and / or protective measures to be taken quickly at the connected electrical installations.

[0005] Conventionally, the detection of the interruption of the neutral connection is based on the detection of an abnormal imbalance between the phase voltages of the distribution network and / or the absence of current flow in the neutral conductor. However, this method is generally unreliable because it does not correctly identify whether the observed imbalance is related to an interruption in the neutral or to an interruption in one or more phases. In addition, the detection of the absence of current through the neutral conductor requires the use of a current sensor positioned on said neutral conductor, which increases the cost and causes physical and electrical implementation problems.

[0006] Another known method for detecting the disconnection of the connection of the neutral wire is to measure the downstream load impedance (of the connected electrical installation) in order to determine the expected imbalance of the phase voltages in the event of disconnection of the neutral connection (and thus to detect when said imbalance actually occurs). However, the effectiveness and reliability of this method are directly related to the reliability of the downstream load impedance measurement. This is a limiting factor because the determination of the expected imbalance between the phase voltages generally uses a theoretical analysis for which the downstream load impedance is assumed to be linear and constant over time (which is not necessarily the case in practice). Moreover, in the case where the interruption of the neutral wire affects a plurality of meters (each having a different (unrelated) and unbalanced downstream load impedance), the aforementioned method is no longer able to detect the interruption of the neutral connection. Indeed, for a given meter, the measured downstream load impedance only takes into account the electrical installation downstream of this meter. However, the imbalance between the phase voltages is related to the equivalent downstream load impedance resulting from the combination of all the downstream load impedances of all the meters affected by the interruption of the neutral connection. Since the equivalent load impedance is not measurable, the aforementioned method is no longer applicable in this case. SUMMARY

[0007] The object of the present invention is a method for detecting the interruption of the connection upstream of the neutral wire of one or more meters in an electrical distribution network in a fast, simple and reliable manner.

[0008] To achieve this object, a method for detecting the interruption of the connection of the neutral wire of a three-phase electrical network is proposed, the detection method being implemented at least partially in a processing unit of an item of electrical equipment connected to the electrical network, and comprising the following steps, repeated periodically:

[0009] - at a time T, acquiring a first phase voltage measured between a first phase and the neutral wire of the three-phase electrical network, a second phase voltage measured between a second phase and the neutral wire, and a third phase voltage measured between a third phase and the neutral wire, the first, second and third phase voltages being measured by a voltage sensor of the item of electrical equipment;

[0010] - evaluating a first quantity representative of the ratio of the maximum phase voltage to the minimum phase voltage from the first, second and third phase voltages;

[0011] - if the first quantity is greater than a predetermined threshold:

[0012] o evaluating at least one second quantity representative of the balance of currents between said first, second and third phase voltages, based on the first, second and third phase voltages;

[0013] o detecting the interruption of the neutral connection at time T when said at least one second quantity satisfies a predetermined reference criterion.

[0014] The detection method according to the application is thus particularly advantageous because it makes it possible to detect the interruption of the neutral connection in the electricity distribution network (upstream of the electricity meter) from a simple measurement of the phase voltages carried by the phase conductors of said network. This detection method is thus simple to implement (as it only requires voltage sensors) and inexpensive.

[0015] Moreover, the detection method according to the application is also highly reliable because, when there is a suspected interruption in the neutral line (i.e. when the first quantity is greater than the predetermined threshold), the second quantity is evaluated and it becomes possible to confirm without doubt that an interruption of the neutral connection has indeed occurred.

[0016] Since this second quantity is evaluated directly on the basis of the phase voltages (this second quantity is evaluated only on the basis of the first, second and third phase voltages and thus does not require any additional measurements), the detection method according to the application can quickly detect the interruption of the neutral connection.

[0017] Moreover, a detection method as previously described is proposed, in which the at least one second quantity comprises a second quantity which is a function of the sum of the pairwise products of the root mean square values of the first, second and third phase voltages.

[0018] Moreover, a detection method as previously described is proposed, in which the second quantity G2 is equal to:

[0019] where V leff , V 2eff and V 3eff are respectively the root mean square value of the first phase voltage, the root mean square value of the second phase voltage and the root mean square value of the third phase voltage,

[0020] the predetermined reference criterion is:

[0021] BorneInf < G2 < BorneSup.

[0022] Moreover, a detection method as previously described is proposed, further comprising the following steps:

[0023] - detecting whether:

[0024] V 1eff = V nom and V 2eff = V nom and V 3eff = V nom ,

[0025] where V nom is the nominal root mean square value of the phase voltages of the electricity network;

[0026] - if this condition is satisfied, BorneInf and BorneSup are defined as follows:

[0027] BorneInf = V nom and

[0028] Further, a detection method is proposed as previously described, wherein if said condition is not satisfied, and if:

[0029] V 1eff = al · V nom and V 2eff = a2 · V nom and V 3eff = a3 · V nom where al, a2 and a3 are real coefficients such that:

[0030] BorneInf = min(B1, B2, B3, B4, B5, B6) and BorneSup = max(B1, B2, B3, B4, B5, B6),

[0031] where

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038] Further, a detection method is proposed as previously described, wherein the at least one second quantity comprises a second quantity as a function of the area of an actual triangle formed by the first, second and third phase voltages in a Frensel diagram.

[0039] Further, a detection method is proposed as previously described, wherein the area of the actual triangle is determined by using the following formula: where A is the second quantity, V leff , V 2eff and V 3eff are the root mean square values of the first, second and third phase voltages, respectively, and is a first phase shift between the first phase voltage and the second phase voltage, is a second phase shift between the second phase voltage and the third phase voltage, and is a third phase shift between the third phase voltage and the first phase voltage, the reference criterion being a second quantity, such that:

[0040] A ref -ε1≤A≤A ref +ε1

[0041] where A ref is the area of the reference triangle, and ε1 is a first predetermined measurement uncertainty.

[0042] Further, it is proposed a detection method as previously described, wherein if the first, second and third phase voltages are perfectly balanced, the area of a predetermined reference triangle is evaluated by using the following formula: A ref -ε1≤A≤A ref +ε1, where A ref is the area of the reference triangle, and V nom is a nominal root mean square value of the phase voltages of the electric power network.

[0043] Further, it is proposed a detection method as previously described, wherein the at least one second quantity comprises a second quantity comprising a first line-to-line voltage U 12 representing the difference between the first phase voltage and the second phase voltage, a second line-to-line voltage U 23 representing the difference between the second phase voltage and the third phase voltage, and a third line-to-line voltage U 31 representing the difference between the third phase voltage and the first phase voltage, then said reference criterion is:

[0044] Φ1-ε2≤U 12 ≤Φ1+ε2 and

[0045] Φ2-ε2≤U 23 ≤Φ2+ε2 and

[0046] Φ3-ε2≤U 31 ≤Φ3+ε2 where Φ1, Φ2 and Φ3 are reference values of the first, second and third line-to-line voltages measured at a reference time T0 before the time T during the operation, and ε2 is a second predetermined measurement uncertainty.

[0047] Moreover, a detection method as previously described is proposed, wherein said at least one second quantity comprises a second quantity comprising a first phase shift between the first phase voltage and the second phase voltage, a second phase shift between the second phase voltage and the third phase voltage, and a third phase shift between the third phase voltage and the first phase voltage, said predetermined reference criterion being that the first, second and third phase shifts are each non-zero and different from 120 degrees. Moreover, a detection method as previously described is proposed, further comprising the step of detecting the interruption of the neutral connection when it has been detected that the second quantity satisfies the predetermined reference criterion for a predetermined number of times, the predetermined number of times corresponding to successive situations in time in which it satisfies the predetermined reference criterion spaced two by two by a predetermined duration.

[0048] Moreover, a detection method as previously described is proposed, wherein when it has been detected that the neutral connection is interrupted, the method further comprises the step of generating an alarm signal, which can be time-stamped in a memory of the electrical equipment item and / or which can be transmitted to an equipment item external to said electrical equipment item.

[0049] An electrical equipment item is also proposed, comprising a voltage sensor and a processing unit arranged to implement a detection method as previously described.

[0050] An electrical equipment item as previously described is also proposed, which is an electricity meter.

[0051] A computer program comprising instructions causing an electrical equipment item as previously described to perform the steps of a detection method as previously described is also proposed.

[0052] A computer-readable storage medium having stored thereon a computer program as previously described is also proposed.

[0053] The application will be better understood in light of the following description of specific, non-limiting embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0054] With reference to the drawings, in which:

[0055] [ Figure 1 ] Figure 1 A three-phase electricity distribution network is shown;

[0056] [ Figure 2 ] Figure 2 A three-phase electricity distribution network in nominal conditions is shown; Figure 1 A Fresnel diagram of the phase voltages of the distribution network shown in Fig. 1 is shown;

[0057] [ Figure 3 ] Figure 3 A three-phase electricity distribution network in nominal conditions is shown; Figure 1 An electronic architecture of a voltage sensor of an electricity meter of the distribution network shown in Fig. 1 is shown;

[0058] [Figure 4 ] Figure 4 the interruption of the neutral connection is shown on the phase voltage of the distribution network; Figure 1 the influence of the interruption of the neutral connection is shown on the phase voltage of the distribution network;

[0059] [ Figure 5 ] Figure 5 the interruption of the neutral connection is shown on the phase voltage of the distribution network; Figure 1 the influence of the interruption of the neutral connection is shown on the phase voltage of the distribution network;

[0060] [ Figure 6 ] Figure 6 the steps of the method for detecting the interruption of the neutral connection according to the present application are shown. DETAILED DESCRIPTION

[0061] Reference Figure 1 , a power distribution network is shown. The distribution network 1 allows for the transmission of electrical power from a power generation unit 2 to one or more electrical installations, in this example a first electrical installation 3 and a second electrical installation 4.

[0062] The distribution network 1 is a three-phase power network, which comprises a first phase conductor 5A, a second phase conductor 5B, a third phase conductor 5C and a neutral conductor 6. For the sake of simplicity, in the following description the term "conductor" will simply be omitted in the description by referring to the first phase 5A, the second phase 5B, the third phase 5C and the neutral 6.

[0063] The distribution network 1 carries a first phase voltage V1 between the first phase 5A and the neutral 6, a second phase voltage V2 between the second phase 5B and the neutral 6 and a third phase voltage V3 between the third phase 5C and the neutral. The first, second and third phase voltages V1, V2, V3 are alternating (sinusoidal) voltages having a frequency of 50 Hz.

[0064] Figure 2 The first phase voltage V1, the second phase voltage V2 and the third phase voltage V3 in a Frensel diagram are shown when the distribution network 1 is operating under nominal conditions.

[0065] The root mean square value V leff of the first phase voltage, the root mean square value V 2eff of the second phase voltage and the root mean square value V 3eff of the third phase voltage are all equal to the nominal root mean square value of the phase voltage, identified as V nom , which is equal to 230 V.

[0066] Furthermore, the first, second and third phase voltages V1, V2, V3 are each out of phase with each other. Thus, a first phase shift exists between the vector representation of the first phase voltage V1 and the vector representation of the second phase voltage V2, a second phase shift Existing between the vector representation of the second phase voltage V2 and the vector representation of the third phase voltage V3, and the third phase shift... It exists between the vector representation of the third-phase voltage V3 and the vector representation of the first-phase voltage V1. First phase shift Second phase shift and the third phase shift Both are equal to 120°. Figure 3 The first line-to-line voltage U corresponding to the difference between the first phase voltage V1 and the second phase voltage V2 is also shown. 12 The second line-to-line voltage U corresponds to the difference between the second phase voltage V2 and the third phase voltage V3. 23 And the third line-to-line voltage U corresponding to the difference between the third phase voltage V3 and the first phase voltage V1. 31 See you again. Figure 1 A first instrument 7 is connected to the distribution network 1 between the power generation unit 2 and the first facility 3. The first instrument 7 is designed to measure the power consumption supplied to the first facility 3 via the distribution network 1. In this case, the first facility 3 is represented by a first impedance Z1 connected between the first phase 5A and the neutral line 6, a second impedance Z2 connected between the second phase 5B and the neutral line 6, and a third impedance connected between the third phase 5C and the neutral line 6. Therefore, during operation under nominal conditions, the first impedance Z1 has a first phase voltage V1 at its terminals, the second impedance Z2 has a second phase voltage V2 at its terminals, and the third impedance Z3 has a third phase voltage V3 at its terminals.

[0067] The second instrument 8 is also connected to the distribution network between the power generation unit 2 and the second facility 4. The second instrument 8 is designed to measure the consumption of electrical power supplied to the second facility 4 via the distribution network 1.

[0068] The first instrument 7 and the second instrument 8 are three-phase instruments.

[0069] The architecture of the first instrument 7 will now be described.

[0070] The first instrument 7 includes a processing unit 7A, which includes at least one processing component. The processing component can be a DSP (Digital Signal Processor), a processor, a microcontroller, an FPGA (Field Programmable Gate Array), or an ASIC (Application-Specific Integrated Circuit).

[0071] The first instrument 7 also includes a memory 7B connected to or integrated into the processing unit 7A. The memory 7B forms a computer-readable storage medium having stored thereon at least one computer program, including instructions for at least partially implementing the detection method described below.

[0072] The first meter 7 also comprises a communication module 7C connected to the processing unit 7A and arranged to transmit data using PLC (Power Line Communication) technology. It should be noted that other communication standards can be used, for example cellular radio technology.

[0073] The first meter 7 also comprises a voltage sensor 7D connected to the processing unit 7A and arranged to measure the first phase voltage VI, the second phase voltage V2 and the third phase voltage V3 of the distribution network 1.

[0074] Reference will now be made to Figure 3 The voltage sensor 7D of the first meter 7 will be described in more detail.

[0075] The voltage sensor 7D comprises a first branch 10, a second branch 11 and a third branch 12.

[0076] The voltage sensor also comprises a first analog-digital converter 13, a second analog-digital converter 14 and a third analog-digital converter 15. For simplicity of description, they will be referred to hereafter as first ADC 13, second ADC 14 and third ADC 15.

[0077] The first branch 10 comprises two first resistors R 1A , R 1B . The first resistor R 1A comprises a first terminal 10A connected to the first phase 5A and a second terminal 10B connected to an input 13A of the first ADC 13. The first resistor R 1B comprises a first terminal 10C connected to the input 13A of the first ADC 13 and a second terminal 10D connected to the neutral wire 6. The two first resistors R 1A , R 1B thereby form a voltage divider bridge between the first phase 5A and the neutral wire 6. A first measurement voltage V 1m thus exists between the input 13A of the first ADC 13 and the neutral wire 6. The first measurement voltage V 1m represents the first phase voltage VI and is coherent with the input voltage range of the first ADC 13.

[0078] The second branch 11 comprises two second resistors R 2A , R 2B . The second resistor R 2A comprises a first terminal 11A connected to the second phase 5B and a second terminal 11B connected to an input 14A of the second ADC 14. The second resistor R 2B comprises a first terminal 11C connected to the input 14A of the second ADC 14 and a second terminal 11D connected to the neutral wire 6. The two second resistors R 2A , R 2Ba voltage divider bridge between the second phase 5B and the neutral line 6 is thus formed. The second measurement voltage V 2m is thus present between the input 14A of the second ADC 14 and the neutral line 6. The second measurement voltage V 2m represents the second phase voltage V2 and is in accordance with the input voltage range of the second ADC 14.

[0079] The third branch 12 comprises two third resistors R 3A , R 3B The third resistors R 3A comprise a first terminal 12A connected to the third phase 5C and a second terminal 12B connected to the input 15A of the third ADC 15. The third resistors R 3B comprise a first terminal 12C connected to the input 15A of the third ADC 15 and a second terminal 12D connected to the neutral line 6. The two third resistors R 3A , R 3B a voltage divider bridge between the third phase 5C and the neutral line 6 is thus formed. The third measurement voltage V 3m is thus present between the input 15A of the third ADC 15 and the neutral line 6. The third measurement voltage V 3m represents the third phase voltage V3 and is in accordance with the input voltage range of the third ADC 15.

[0080] The voltage divider bridge of each of the first, second and third branches 10, 11, 12 makes it possible to reduce the amplitude of the first, second and third phase voltages V1, V2, V3, respectively, in order to make them compatible with the measurement range of the first ADC 13, the second ADC 14 and the third ADC 15.

[0081] The first ADC 13 comprises an output 13B connected to the processing unit 7A. The first ADC 13 thus generates and provides to the processing unit 7A a first measurement sample representing the first phase voltage V1. The second ADC 14 comprises an output 14B connected to the processing unit 7A. The second ADC 14 thus generates and provides to the processing unit 7A a second measurement sample representing the second phase voltage V2.

[0082] The third ADC 15 comprises an output 15B connected to the processing unit 7A. The third ADC 15 thus generates and provides to the processing unit 7A a third measurement sample representing the third phase voltage V3.

[0083] It is assumed that the first ADC 13, the second ADC 14 and the third ADC 15 each have a correct conversion of the first measurement voltage V 1m , the second measurement voltage V 2m and the third measurement voltage V 3mof the appropriate characteristics (number of bits, sampling frequency) of the first, second and third ADCs 13, 14, 15. In this case, the first, second and third ADCs 13, 14, 15 all have a number of bits greater than or equal to 12 and a sampling frequency of at least 2 ksps (kilo samples per second).

[0084] The effect of the interruption of the connection of the neutral line 6 in the distribution network 1 will now be described.

[0085] Referring to Figure 4 , it is assumed that the interruption of the connection of the neutral line 6 occurs at a break point 16 in the distribution network 1 upstream of the first meter 7. The term “upstream” is to be understood as meaning on the side of the electricity generation unit 2 and the term “downstream” is to be understood as meaning on the side of the first installation 3.

[0086] When the interruption of the connection of the neutral line 6 occurs, the node 17 becomes a floating node.

[0087] The first phase voltage VI downstream of the break point 16 then spontaneously balances according to the first impedance Zl of the first installation 3. The first impedance Zl thus has at its terminals the first phase voltage VI which is the voltage carried by the first phase 5A downstream of the break point 16. The first phase voltage VI is represented as a function of the first nominal phase voltage V 10 (which is the voltage carried by the first phase 5A upstream of the break point 16) and the potential difference V ne caused by the interruption of the connection of the neutral line 6.

[0088] VI = VI - V 10 - V ne .

[0089] Similarly, the second phase voltage V2 downstream of the break point 16 spontaneously balances according to the second impedance Z2 of the first installation 3. The second impedance Z2 thus has at its terminals the second phase voltage V2 which is the voltage carried by the second phase 5B downstream of the break point 16. The first phase voltage V2 is represented as a function of the second nominal phase voltage V 20 (which is the voltage carried by the second phase 5B upstream of the break point 16) and the potential difference V ne :

[0090] V2 = V2 - V 20 - V ne .

[0091] Similarly, the third phase voltage V3 downstream of the break point 16 spontaneously balances according to the third impedance Z3 of the first installation 3. The third impedance Z3 thus has at its terminals the third phase voltage V3 which is the voltage carried by the third phase 5C downstream of the break point 16. The third phase voltage V3 is represented as a function of the third nominal phase voltage V 30 (which is the voltage carried by the third phase 5C upstream of the break point 16) and the potential difference Vne Functions:

[0092] V3 = V 30 -V ne .

[0093] It should be noted that when the neutral line 6 is connected correctly, V1 = V 10 V2 = V 20 And V3 = V 30 .

[0094] See Figure 5 The Fresnel diagram illustrates the effect of the interruption of the connection of neutral line 6.

[0095] Interestingly, it is noted that the interruption of the connection of neutral line 6 causes the first phase voltage V1, the second phase voltage V2, and the third phase voltage V3 to rebalance with each other. Except in specific scenarios where the first, second, and third resistors Z1, Z2, and Z3 are completely balanced in the first, second, and third phases 5A, 5B, and 5C, the new balance will be different from the initial balance (when neutral line 6 is correctly connected).

[0096] The new equilibrium involves the root mean square value V of the first phase voltage. leff The root mean square value V of the second phase voltage 2eff and the root mean square value V of the third phase voltage 3eff The changes in voltage, and then these changes are no longer necessarily equal to the nominal root mean square value V of the phase voltage. nom .

[0097] The new equilibrium also involves the first phase shift. Second phase shift and the third phase shift The changes, then, these changes are no longer necessarily all equal to 120°.

[0098] However, the new balance maintains the first line-to-line voltage U. 12 Second line-to-line voltage U 23 and the third line-to-line voltage U 31 .

[0099] See Figure 6 The steps of the method for detecting a break in a neutral line connection according to the present invention will now be described.

[0100] The detection method according to the invention is implemented in the processing unit 7A of the first instrument 7. More specifically, the detection method according to the invention is continuously implemented by the processing unit 7A of the first instrument. The steps of the detection method are therefore repeated periodically over time.

[0101] The method begins at time T by acquiring the first phase voltage V1 between the first phase 5A and the neutral line 6, the second phase voltage V2 between the second phase 5B and the neutral line 6, and the third phase voltage V3 between the third phase 5C and the neutral line 6 (step E1).

[0102] More specifically, the processing unit 7A acquires a first measurement sample representing the first phase voltage V1, a second measurement sample representing the second phase voltage V2, and a third measurement sample representing the third phase voltage V3. The first, second, and third measurement samples are transmitted to the processing unit 7A by the voltage sensor 7D.

[0103] Using the first measurement sample, the second measurement sample, and the third measurement sample respectively, the processing unit 7A determines (possibly by applying calibration parameters) the root mean square value V of the first phase voltage. leff The root mean square value V of the second phase voltage 2eff and the root mean square value V of the third phase voltage 3eff In this case, the root mean square value V 1eff V 2eff and V 3eff The root mean square value V is determined per second by processing unit 7A based on the first, second, and third measurement samples acquired in the previous second. 1eff V 2eff and V 3eff It can also be determined within a sliding second or within any other suitable time window.

[0104] Next, processing unit 7A defines and / or updates predetermined reference criteria (step E2). The predetermined reference criteria will be described below.

[0105] It should be noted that step E2 is optional. In fact, the predetermined reference criteria can be determined at a single time during the installation of the first instrument 7 in the distribution network 1 (the predetermined reference criteria are stored in the memory 7B). The predetermined reference criteria can also be defined and / or updated during the maintenance of the first instrument 7.

[0106] Then, processing unit 7A evaluates a first quantity representing the ratio of the maximum phase voltage to the minimum phase voltage based on the first, second, and third phase voltages V1, V2, and V3 (step E3). More specifically, in this case, the first quantity is a number M determined using the following formula:

[0107]

[0108] The evaluation of the first quantity M makes it possible to check whether there is an imbalance between the first, second and third phase voltages V1, V2, V3. To this end, the first quantity M is compared with a predetermined threshold (step E4). This predetermined threshold is equal to 1.2 in this case, in order to specifically take into account the normal dispersion of the first, second and third phase voltages V1, V2, V3, inherent in the distribution network 1. If the first quantity M is greater than the predetermined threshold, there is a significant imbalance between the first, second and third phase voltages V1, V2, V3, and this constitutes a first indicator of a suspected disconnection of the connection of the neutral wire 6 in the distribution network 1 upstream of the first meter 7.

[0109] However, the simple fact that the first quantity M is greater than the predetermined threshold is not sufficient to determine that the interruption of the connection of the neutral wire 6 has actually occurred. In particular, a simple interruption of the connection of one phase (from the first, second and third phases 5A, 5B, 5C) can also lead to the same observation (the first quantity M is greater than the predetermined threshold). It is therefore necessary to confirm the suspected interruption of the connection of the neutral wire by determining an indicator of the characteristics of the interruption of the neutral wire connection in a three-phase power network.

[0110] It should be noted that if the first quantity M is less than the predetermined threshold, the detection method according to the application determines that there is no interruption of the connection of the neutral wire 6, and therefore returns to step E1.

[0111] If the first quantity is greater than the predetermined threshold, the processing unit 7A evaluates at least one second quantity representative of the balance of currents between said first, second and third phase voltages, on the basis of the first phase voltage V1, the second phase voltage V2 and the third phase voltage V3 (step E5). Indeed, as shown in Figure 5 The interruption of the connection of the neutral wire causes a new balance between the first, second and third phase voltages V1, V2, V3.

[0112] The processing unit 7A then detects whether the at least one second quantity satisfies a predetermined reference criterion.

[0113] Now several methods are possible, and in particular several different second quantities and several predetermined reference criteria can be defined in order to effectively confirm that an interruption of the connection of the neutral wire 6 has occurred.

[0114] According to a first embodiment, the at least one second quantity comprises a second quantity G2, which is a function of the sum of the pairwise products of the first, second and third phase voltages V1, V2, V3. More specifically, the second quantity G2 is the sum of the pairwise products of the first, second and third phase voltages V1, V2, V3, of the root mean square values V leff , V 2eff , V 3effthe sum of the pairwise products of the first, second and third phase voltages V1, V2, V3. The approach presented here is based on the fact that when there is a suspected interruption of the neutral line connection, the first, second and third phase voltages V1, V2, V3 become balanced according to a new balance, which is not completely random.

[0115] If one of the root mean square values V 1eff , V 2eff , V 3eff of the phase voltages from the first, second and third phase voltages V1, V2, V3 decreases sharply, while the other two root mean square values remain constant, this does not indicate an interruption of the neutral line 6 connection. For example, if the root mean square value V 1eff decreases sharply while the root mean square values V 2eff and V 3eff remain constant, then it is a matter of a voltage drop in the first phase 5A or an interruption of the connection of said first phase 5A. However, if one of the root mean square values V 1eff , V 2eff , V 3eff of the phase voltages from the first, second and third phase voltages V1, V2, V3 decreases sharply and at the same time, one of the other two root mean square values increases (or indeed both root mean square values increase), then this is very likely to be associated with an interruption of the connection of the neutral line 6. For example, if the root mean square value V 1eff decreases sharply and the root mean square values V 2eff and V 3eff increase at the same time, then this is very likely to be associated with an interruption of the connection of the neutral line 6.

[0116] Similarly, if one of the root mean square values V 1eff , V 2eff , V 3eff of the phase voltages from the first, second and third phase voltages V1, V2, V3 increases sharply, while the other two root mean square values remain constant, this does not indicate an interruption of the neutral line 6 connection.

[0117] In order to confirm a suspected interruption of the neutral line 6 connection, the processing unit 7A calculates a second quantity G2 by using the following formula:

[0118]

[0119] where V 1eff , V 2eff and V 3eff are the root mean square value of the first phase voltage, the root mean square value of the second phase voltage and the root mean square value of the third phase voltage, respectively.

[0120] The second quantity G2 is proposed because it is limited when the connection of the neutral line 6 occurs to be broken. In the first embodiment, the predetermined reference criterion defined by the processing unit 7A therefore checks that the second quantity G2 is limited between a lower limit BorneInf and an upper limit BorneSup:

[0121] BorneInf < G2 < BorneSup.

[0122] In order to correctly define BorneInf and BorneSup, the detection method further comprises the following steps:

[0123] - detecting whether the first, second and third phase voltages VI, V2, V3 are perfectly balanced, i.e. whether the root mean square value V leff of the first phase voltage, the root mean square value V 2eff of the second phase voltage and the root mean square value V 3eff of the third phase voltage are all equal to the nominal root mean square value V nom of the phase voltages of the distribution network 1:

[0124] V 1eff = V nom and V 2eff = V nom and V 3eff = V nom ,

[0125] - if this condition is satisfied, BorneInf and BorneSup are defined as follows:

[0126] BorneInf = V nom and

[0127]

[0128] Otherwise, if said condition is not satisfied, and therefore if:

[0129] V 1eff = a1-V nom and V 2eff = a2-V nom and V 3eff = a3-V nom where a1, a2 and a3 are real coefficients, whereby a1≠ a2≠ a3 and V nom is said nominal root mean square value:

[0130] BorneInf = min(B1, B2, B3, B4, B5, B6) and

[0131] BorneSup = max(B1, B2, B3, B4, B5, B6),

[0132] wherein

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139] Appendix 1 presents a mathematical demonstration for determining the representation of BornInf and BornSup.

[0140] If the second quantity G2 is limited between the lower limit BornInf and the upper limit BornSup (i.e. if the second quantity G2 satisfies a predetermined reference criterion), the detection method according to the present application detects the interruption of the neutral connection upstream of the first meter 7 at the time T.

[0141] In the first embodiment, it is also possible to detect the disconnection of the neutral connection 6 when one of the first phase 5A, the second phase 5B and the third phase 5C is disconnected. In this case, consider that the third phase 5C is disconnected. If a disconnection of the neutral connection 6 occurs, there is a characteristic relationship between the root mean square value V 1eff of the first phase voltage and the root mean square value V 2eff of the second phase voltage. If the first, second and third phase voltages V1, V2, V3 are perfectly balanced, i.e. if: V 1eff = V nom and V 2eff = V nom and V 3eff = V nom , the characteristic relationship is as follows:

[0142] where V nom is the nominal root mean square value of the phase voltage.

[0143] If the first, second and third phase voltages V1, V2, V3 are not perfectly balanced, i.e. if: V 1eff = a1 · V nom and V 2eff = a2 · V nom and V nom = a3 · V nom , (a1 ≠ a2 ≠ a3), the characteristic relationship is as follows:

[0144] where V nomis the nominal root mean square value of the phase voltage.

[0145] A more complete and detailed algorithm for implementing the detection method according to the first embodiment of the application is presented in Appendix 2.

[0146] According to a second embodiment, the detection method comprises a step of evaluating at least one second quantity, the second quantity comprising a second quantity A, the second quantity being a function of the area of the actual triangle 19 formed by the first, second and third phase voltages V1, V2, V3 in the Frensel diagram.

[0147] The actual triangle 19 has a first side constituted by the first line-line voltage U 12 , a second side constituted by the second line-line voltage U 23 , and a third side constituted by the third line-line voltage U 31 .

[0148] The processing unit 7A determines the second quantity A by using the following formula:

[0149] where A is the second quantity (which is the area of the actual triangle 19), V 1eff , V 2eff and V 3eff are the root mean square values of the first, second and third phase voltages, respectively, and is the first phase shift, is the second phase shift, and is the third phase shift. The processing unit 7A determines the first phase shift the second phase shift and the third phase shift based on the first, second and third phase voltages V1, V2, V3 by the zero-crossing method and appropriate filtering.

[0150] Then, the reference criterion is that the second quantity A is such that:

[0151] A ref - ε1≤ A ≤ A ref + ε1, where A ref is the predetermined area of the reference triangle 18 and ε1 is the first predetermined measurement uncertainty (typically + / - 1% or + / - 2%).

[0152] Referring to Figure 5 , the area of the reference triangle 18A ref is in fact the area of the triangle formed by the first, second and third phase voltages V1, V2, V3 in the Frensel diagram under nominal conditions (i.e. when there is no interruption of the connection of the neutral line 6).

[0153] In practice, it is interesting to note that, in the case of disconnection of the connection of the neutral wire 6, the area of the reference triangle 18 is similar to the area of the actual triangle 19. Therefore, by comparing the second quantity A (area of the actual triangle 19) with the predetermined area of the reference triangle 18A ref , it is possible to effectively determine whether a disconnection of the connection of the neutral wire 6 has occurred.

[0154] In order to correctly define the area of the reference triangle 18A ref , the detection method further comprises the following steps:

[0155] - detecting whether the first, second and third phase voltages V1, V2, V3 are perfectly balanced, i.e. whether the root mean square value V leff of the first phase voltage, the root mean square value V 2eff of the second phase voltage and the root mean square value V 3eff of the third phase voltage are all equal to the nominal root mean square value V nom of the phase voltages of the distribution network 1:

[0156] V 1eff = V nom and V 2eff = V nom and V 3eff = V nom ,

[0157] - if this condition is satisfied, the area of the reference triangle 18 is evaluated by using the following formula: where V nom is the nominal root mean square value of the phase voltages.

[0158] Otherwise, if said condition is not satisfied, and therefore if:

[0159] V 1eff = a1 · V nom and V 2eff = a2 · V nom and V 3eff = a3 · V nom , where a1, a2 and a3 are real coefficients such that a1≠a2≠a3 and V nom is the nominal root mean square value of the phase voltages, the area of the reference triangle 18 is evaluated by using the following formula: where V nom is said nominal root mean square value of the phase voltages.

[0160] If the second quantity A satisfies the predetermined reference criterion, the detection method according to the present application detects a disconnection of the neutral connection upstream of the first meter 7 at the time T.

[0161] According to a third embodiment of the application, the at least one second quantity comprises second quantities including a first line-line voltage U 12 , a second line-line voltage U 23 and a third line-line voltage U 31 .

[0162] With reference to Figure 5 , in case of disconnection of the neutral line 6, the first line-line voltage U 12 , the second line-line voltage U 23 and the third line-line voltage U 31 remain constant.

[0163] The reference criterion checked by the processing unit 7A is therefore to check whether:

[0164] Φ1-ε2≤ U 12 ≤ Φ1+ε2 and

[0165] Φ2-ε2≤ U 23 ≤ Φ2+ε2 and

[0166] Φ3-ε2≤ U 31 ≤ Φ3+ε2,

[0167] where Φ1, Φ2 and Φ3 are reference values of the first, second and third line-line voltages U 12 , U 23 , U 31 measured during the operation at a reference time T0 preceding the time T, while ε2 is a second predetermined measurement uncertainty (typically + / - 1% or + / - 2%).

[0168] If the second quantities U 12 , U 23 and U 31 satisfy the predetermined reference criterion, the detection method according to the application detects the interruption of the neutral line connection upstream of the first meter 7 at the time T.

[0169] According to a fourth embodiment of the application, the detection method comprises the step of evaluating at least one second quantity comprising second quantities including a first phase shift a second phase shift and a third phase shift

[0170] With reference to Appendix 1 : Formal presentation of the relationships proposed for the first embodiment , it is interesting to note that, when the interruption of the neutral line 6 connection occurs, the first phase shift the second phase shift and the third phase shift are no longer equal to 120°.

[0171] If the first phase shift the second phase shift and the third phase shift each non-zero and different from 120 degrees, the reference criterion defined by the processing unit 7A is satisfied.

[0172] if the first phase shift the second phase shift and the third phase shift The detection method according to the application detects the interruption of the neutral connection upstream of the first meter 7 at time T if the predetermined reference criterion is satisfied.

[0173] In the four embodiments of the application disclosed above, if the one or more second quantities do not satisfy the predetermined reference criterion, the detection method moves to a step E1’ similar to step E1 and possibly comprises a step E2’ similar to step E2.

[0174] In the four embodiments of the application disclosed above, an appropriate uncertainty margin is taken into account, in particular related to the accuracy of the voltage sensor 7D of the first meter 7. Typically, the uncertainty margin is in the region of + / - 1% or + / - 2%. In the four embodiments of the application disclosed above, the expressions of the definitions of the predetermined reference criterion (BornInf, Bornsup, A ref , Φ1, Φ2 and Φ3) can be determined by the processing unit 7A through several successive calculations in order to mitigate parasitic phenomena (such as transient overvoltages of the shock wave or micro-cut-off type) which can reduce the reliability of the detection method according to the application. The use of averaging techniques is quite feasible assuming that the distribution network 1 is stable over a given period of time.

[0175] Irrespective of the embodiment, the detection method according to the application is continuously implemented by the processing unit 7A of the first meter. The steps of said detection method are therefore repeated at regular times.

[0176] Advantageously, and irrespective of the embodiment, the detection method according to the application can further comprise the step of detecting the interruption of the neutral connection 6 when the second quantity has been detected to satisfy the predetermined reference criterion a predetermined number of times (for example, 10 times), corresponding to successive situations in which it is satisfied (i.e. the continuous implementation of the detection method), these successive situations being spaced apart from each other in time by a predetermined duration (for example, 1 second). This improves the reliability of the detection method according to the application.

[0177] Optionally, when the disconnection of the neutral connection has been effectively detected, the detection method can further comprise the step of generating an alert signal which can be time-stamped in the memory 7B of the first meter 7 and / or can be transmitted (via the communication module 7C) to equipment items external to said first meter 7, for example the information system of the distribution network 1.

[0178] Optionally, the alarm signal can be the display of a specific message on the local display of the first meter 7 and / or the alarm signal can be the lighting of an indicator light located on said first meter 7 and / or the emission of a sound signal through a loudspeaker of the first meter 7.

[0179] Ideally, all the electricity meters of the distribution network 1 are similar and arranged for implementing the detection method according to the application. Thus, the whole distribution network 1 is properly monitored.

[0180] Optionally, when the interruption of the neutral connection has been effectively detected and the imbalance between the first phase voltage, the second phase voltage and the third phase voltage is considered to be too large, if said detection method is implemented in a specific meter comprising a circuit breaker, the detection method can further comprise the step of opening said circuit breaker in order to protect one or more electrical installations downstream said specific meter.

[0181] Naturally, the application is not limited to the implementation examples described, but encompasses any variants falling within the scope of the application as defined by the claims.

[0182] It is quite possible to freely combine the different embodiments disclosed above. Thus, the processing unit 7A of the first meter 7 can determine several second quantities, for example the second quantity G2 (disclosed in the first embodiment) and the second quantity A (disclosed in the second embodiment). This can improve the reliability of the detection method according to the application.

[0183] The voltage sensors 7D of the first meter 7 have been disclosed as comprising a first ADC 13, a second ADC 14 and a third ADC 15, but they can quite possibly comprise a single ADC comprising three different inputs each respectively acquiring the first phase voltage, the second phase voltage and the third phase voltage.

[0184] Figure 4

[0185] The assumption of the demonstration is that the first, second and third phase voltages V1, V2, V3 are perfectly balanced, i.e. the root mean square values V 1eff , V 2eff , V 3eff all equal the nominal root mean square value V nom of the phase voltage. This is not necessarily accurate in practice, but can be used as a first approach.

[0186] It should be noted that the voltages in the demonstration are in vector form and throughout the demonstration they are complex root mean square values.

[0187] Referring to Calculation of V1Once the interruption of the neutral connection has occurred, it is possible to write:

[0188]

[0189]

[0190]

[0191]

[0192] I1, I2, I3 are the currents flowing through the first phase 5A, the second phase 5B and the third phase 5C, respectively.

[0193]

[0194] Using the first admittance Y1, the second admittance Y2 and the third admittance Y3 (Y1 = 1 / Z1, Y2 = 1 / Z2, Y3 = 1 / Z3), the following holds:

[0195]

[0196] Substituting (1) is fulfilled

[0197]

[0198] Calculation of V2

[0199] Because:

[0200]

[0201]

[0202] Based on relation (1), the following holds:

[0203]

[0204]

[0205]

[0206] Applying the modulus gives: (2)

[0207]

[0208] Calculation of V3

[0209] Based on relation (1), the following is applied:

[0210]

[0211] Because:

[0212]

[0213] Hence:

[0214]

[0215]

[0216] Applying the modulus gives: (3)

[0217]

[0218] Appendix 2 Algorithm proposed for the first embodiment

[0219] Based on relation (1), apply the following:

[0220]

[0221] Because:

[0222]

[0223] Hence:

[0224]

[0225]

[0226] Applying the modulus gives: (4)

[0227]

[0228] Using relations (2), (3) and (4) and locating V 10 = V nom gives:

[0229]

[0230] where:

[0231]

[0232]

[0233]

[0234] Study the limit case:

[0235] Case 1: Y1 = Y2 = Y3 = Y:

[0236]

[0237] Because:

[0238]

[0239] Thus (the limit case studied here constitutes the lower bound) - V i and V j are the phase voltages of the i-th and j-th phase, respectively:

[0240]

[0241] Therefore:

[0242]

[0243] Case 2: Y1 = Y2 = Y > Y3 = y:

[0244]

[0245] Because:

[0246]

[0247] Thus (the limit case studied here constitutes the upper bound):

[0248]

[0249] Therefore:

[0250]

[0251] By studying the limit cases, we have shown that, in the event of the interruption of the neutral connection, the sum of the V i V j is very precisely limited between V nom and 1.056 V nom :

[0252]

[0253] BorneInf = V nom

[0254]

[0255] The proposed formula can then be generalized by the same calculation process in order to take into account the initial conditions in which the distribution network does not have a perfectly balanced phase voltage by positioning:

[0256] V 1eff = a1 · V nom and V 2eff = a2 · V nom and V 3eff = a3 · Vnom where a1, a2 and a3 are real coefficients such that a1≠a2≠a3.

[0257] In fact, considering the effect of the initial unbalance between the phase voltages from the distribution network, due to the loss of symmetry, the asymptotic study cases to be considered (which make it possible to obtain a bounded limit of the expected results in the case of interruption of the neutral connection) increase from 2 to 6.

[0258] The 6 limits are given by:

[0259]

[0260]

[0261]

[0262]

[0263]

[0264]

[0265] And finally:

[0266]

[0267] where:

[0268] BorneInf = min(B1, B2, B3, B4, B5, B6) and

[0269] BornSup = max(B1, B2, B3, B4, B5, B6).

[0270] ​

[0271]

[0272]

[0273]

[0274]

[0275]

Claims

1. A method for detecting an interruption in the connection of the neutral line (6) of a three-phase power network, said method being implemented at least in part in a processing unit (7A) of an electrical equipment (7) item connected to said power network (1), and comprising the following steps repeated periodically: - At time T, the first phase voltage (V1) between the first phase (5A) and the neutral line (6) of the three-phase power network, the second phase voltage (V2) between the second phase (5B) and the neutral line (6) of the three-phase power network, and the third phase voltage (V3) between the third phase (5C) and the neutral line (6) of the three-phase power network are collected. The first, second and third phase voltages are measured by the voltage sensor (7D) of the electrical equipment (7). - The evaluation is a first quantity representing the ratio of the maximum phase voltage to the minimum phase voltage from the first, second, and third phase voltages; The method is characterized in that: - if the first quantity is greater than a predetermined threshold: To evaluate at least one second quantity representing the current balance among the first, second, and third phase voltages based solely on the first, second, and third phase voltages; and When the at least one second quantity satisfies a predetermined reference criterion, an interruption in the connection of the neutral line (6) is detected at time T.

2. The method as described in claim 1, characterized in that, The at least one second quantity includes a second quantity that is a function of the sum of the pairwise products of the root mean square values ​​of the first phase voltage, the second phase voltage, and the third phase voltage.

3. The method as described in claim 2, characterized in that, The second quantity G2 is equal to: , Where V 1eff V 2eff and V 3eff These are the root mean square values ​​of the first phase voltage (V1), the second phase voltage (V2), and the third phase voltage (V3), respectively.

4. The method as described in claim 3, characterized in that, The predetermined reference criteria are: Where BorneInf and BorneSup are the lower and upper limits of G2, respectively, the method further includes the following steps: - Check if the following conditions are met: ， Where V nom It is the nominal root mean square value of the phase voltage of the power network; - If the above conditions are met, then define BorneInf and BorneSup as follows: as well as .

5. The method as described in claim 4, characterized in that, If the stated conditions are not met, and if: Where a1, a2, and a3 are real coefficients such that ,but: as well as , in 。 6. The method as described in claim 1, characterized in that, The at least one second quantity includes a second quantity that is a function of the area of ​​the actual triangle (19) formed by the first, second and third phase voltages in the Fresnel diagram.

7. The method as described in claim 6, characterized in that, The area of ​​the actual triangle is determined using the following formula: Where A is the second quantity, V 1eff V 2eff and V 3eff These are the root mean square values ​​of the first, second, and third phase voltages, respectively. It is the first phase shift between the first phase voltage and the second phase voltage. It is the second phase shift between the second phase voltage and the third phase voltage, and It is the third phase shift between the third phase voltage and the first phase voltage, and the predetermined reference criterion is the second quantity, such that: , Where A ref It is the area of ​​the reference triangle, and ε1 is the first predetermined measurement uncertainty.

8. The method as described in claim 7, characterized in that, If the first, second, and third phase voltages are perfectly balanced, the area of ​​the reference triangle (18) is evaluated using the following formula: A ref It is the area of ​​the reference triangle, and V nom It is the nominal root mean square value of the phase voltage of the power network.

9. The method as described in claim 1, characterized in that, The at least one second quantity includes a second quantity, the second quantity including a first line-to-line voltage representing the difference between the first phase voltage and the second phase voltage. The second line-to-line voltage represents the difference between the second phase voltage and the third phase voltage. And the third line-to-line voltage representing the difference between the third phase voltage and the first phase voltage. Then the predetermined reference criterion is: and and Wherein Φ1, Φ2 and Φ3 are reference values ​​of the first, second and third line-to-line voltages measured during operation at a reference time T0 prior to time T, and ε2 is the second predetermined measurement uncertainty.

10. The method as described in claim 1, characterized in that, The at least one second quantity includes a second quantity comprising a first phase shift between the first phase voltage (V1) and the second phase voltage (V2), a second phase shift between the second phase voltage (V2) and the third phase voltage (V3), and a third phase shift between the third phase voltage (V3) and the first phase voltage (V1), wherein the predetermined reference criterion is that the first, second, and third phase shifts are each non-zero and different from 120 degrees.

11. The method as described in any one of the preceding claims, characterized in that, It also includes the step of detecting an interruption of the neutral line connection when the second quantity has been detected to satisfy the predetermined reference criterion a predetermined number of times, the predetermined number of times corresponding to a series of successive checks at predetermined time intervals.

12. The method according to any one of claims 1-10, characterized in that, When an interruption in the neutral line connection has been detected, the method further includes the step of generating an alarm signal that can be timestamped in the memory (7B) of the electrical equipment and / or can be transmitted to equipment outside the electrical equipment.

13. An electrical device comprising a voltage sensor and a processing unit (7A), said processing unit being arranged to implement the method according to any one of the preceding claims.

14. The electrical equipment as claimed in claim 13, characterized in that, The electrical equipment item is the instrument (7).

15. A computer program product comprising instructions that cause the electrical equipment according to claim 13 or 14 to perform the method according to any one of claims 1 to 12.

16. A computer-readable storage medium having a computer program stored thereon, the computer program including instructions that cause the electrical equipment according to claim 13 or 14 to perform the method according to any one of claims 1 to 12.

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