Virtual estimation of the temperature of a current transformer

Abstract

Electricity meter (1) comprising: a current transformer (17) arranged to produce initial measurements of a current (Iph) flowing in a winding (20) of the current transformer; a temperature sensor; a processing unit (8) arranged to evaluate an estimated current (Ie) and an internal temperature (Ti), to evaluate an estimated temperature (Te) of the winding (20) from the estimated current and the internal temperature, and to evaluate, from the estimated temperature, a measurement phase shift ( ) produced by the current transformer on the initial measurements, the measurement phase shift being intended to be used to measure the electrical energy consumed. FIGURE IN ABRIDGED DIAGRAM: Fig. 1

Description

Title of the invention: Virtual estimation of the temperature of a current transformer

[0001] The invention relates to electric meters incorporating at least one current transformer.

[0002] BACKGROUND

[0003] An electricity meter measures the electrical energy supplied by a distribution network (polyphase or single-phase) to an installation. Measuring electrical energy requires measuring the current(s) supplied to the installation. To measure this current(s), it is known to integrate one or more internal current transformers into the meter.

[0004] The accuracy requirement for measuring the electrical energy consumed by the installation is very stringent: 0.5%, or even as low as 0.2% or 0.1%. This requirement must be met, in particular, during the self-heating tests of the current transformers.

[0005] It is known that a current transformer generates a phase shift A in current measurements, which, if not compensated, causes significant inaccuracy in the measurement of energy consumed. This inaccuracy makes it impossible to maintain the accuracy classes just mentioned.

[0006] The phase shift A depends on the temperature of the current transformer windings, and in particular on the temperature of the secondary winding through which the image of the current supplied to the installation flows. It is therefore necessary to accurately estimate the winding temperature. This allows for a precise estimation of the phase shift A tp(t\) and thus for effective compensation of this phase shift to obtain a sufficiently accurate measurement of the energy consumed.

[0007] A temperature sensor is typically integrated into the meter's casing. This is, for example, an NTC thermistor (for Negative Temperature Coefficient). The most obvious solution is therefore to use this temperature measurement to estimate the phase shift A q^t)-

[0008] However, experience shows that the temperature drops very rapidly as one moves away from the transformer windings and that, even if the thermistor is close to the windings, it does not accurately reflect the winding temperature. The resulting estimate of the winding temperature is therefore too imprecise to meet the accuracy classes mentioned.

[0009] We therefore considered mounting a temperature sensor directly on each transformer. This solution generates a certain additional cost and complexity. Design considerations, particularly in polyphase meters (integrating a number of temperature sensors equal to the number of transformers), are problematic. Furthermore, the transformer windings are encased in a plastic sheath. Therefore, positioning the temperature sensor on the plastic sheath provides a very inaccurate assessment of the actual winding temperature.

[0010] OBJECT

[0011] The invention aims to evaluate the phase shift on current measurements, caused by a current transformer integrated into an electric meter, in a precise, simple and inexpensive manner.

[0012] SUMMARY

[0013] To achieve this goal, an electricity meter is proposed, arranged to measure electrical energy supplied to an installation by a distribution network, the electricity meter comprising: - a current measurement device, comprising a current transformer, and arranged to produce initial measurements representative of a current flowing in a winding of the current transformer; - a temperature sensor, arranged to produce second measurements representative of an internal temperature prevailing inside the meter; - a processing unit designed for: • evaluate an estimated current from the first measurements, and the internal temperature from the second measurements; • Evaluate an estimated winding temperature from the estimated current and internal temperature; • evaluate, from the estimated temperature, a measurement phase shift produced by the current transformer on the first measurements, the measurement phase shift being intended to be used to measure said electrical energy.

[0014] By using not only the internal temperature inside the meter, but also the estimated current calculated from the initial measurements produced by the current measuring device, the processing unit is able to evaluate the temperature of the current transformer winding very accurately and in real time. The processing unit can therefore evaluate the measurement phase shift very precisely, and thus produce a very accurate estimate of the energy consumed by the installation. The stringent accuracy requirements for measuring electrical energy consumption are met. This method of estimating the winding temperature does not require any additional hardware components, and is therefore very simple and inexpensive to implement.

[0015] An electric meter as previously described is also proposed, in which the processing unit is arranged to apply a low-pass filter to the first measurements to obtain the estimated current.

[0016] We further propose an electricity meter as previously described, in which the low-pass filter is a first-order Butterworth filter.

[0017] We further propose an electric meter such as previously described, in which the estimated temperature is evaluated from the estimated current raised to the square.

[0018] An electricity meter as previously described is further proposed, comprising a plurality of current measuring devices, each including a current transformer, the processing unit being arranged, for each current transformer, to evaluate the estimated temperature of a winding of said current transformer from:

[0019] - of the internal temperature,

[0020] - the estimated current for said current transformer, and

[0021] - also using an approximate temperature of a winding of at least one other current transformer, the approximate temperature of the winding of at least one other current transformer being evaluated from the internal temperature and the estimated current for at least one other current transformer.

[0022] An electric meter as previously described is further proposed, in which at least one other current transformer includes the current transformer positioned closest to said current transformer.

[0023] An electric meter as previously described is further proposed, in which the electric meter comprises a first current measuring device including a first current transformer arranged to measure a current flowing on a first phase, a second current measuring device including a second current transformer arranged to measure a current flowing on a second phase, and a third current measuring device including a third current transformer arranged to measure a current flowing on a third phase,

[0024] the second current transformer being positioned between the first current transformer and the third current transformer,

[0025] the processing unit being arranged for:

[0026] - evaluate the estimated temperature of the winding of the first transformer of current also using the approximate temperature of the winding of the second current transformer;

[0027] - evaluate the estimated temperature of the winding of the second transformer current, also using the approximate temperature of the first winding current transformer and the approximate temperature of the winding of the third current transformer;

[0028] - evaluate the estimated temperature of the winding of the third transformer of current also using the approximate temperature of the winding of the second current transformer.

[0029] An electric meter as previously described is also proposed, the electric meter being a single-phase meter comprising a single current measuring device, including a current transformer and arranged to measure a current flowing on a neutral.

[0030] An electricity meter as previously described is also proposed, in which:

[0031] - the current transformer(s) are positioned on a first side among a left side and a right side of the electric meter, and in a first part between an upper part and a lower part of the electric meter;

[0032] - the temperature sensor is positioned on a second side and in a second part of the electricity meter.

[0033] A measurement method is further proposed, implemented in the processing unit of the electricity meter as previously described, and comprising the steps of: • evaluate an estimated current from the first measurements, and the internal temperature from the second measurements; • Evaluate an estimated winding temperature from the estimated current and internal temperature; • evaluate, from the estimated temperature, a measurement phase shift produced by the current transformer on the first measurements, the measurement phase shift being intended to be used to measure said electrical energy.

[0034] A computer program is also proposed comprising instructions which lead the processing unit of the electric meter as previously described to execute the steps of the measurement process as previously described.

[0035] A computer-readable recording medium is also proposed, on which the computer program as previously described is recorded.

[0036] The invention will be better understood in the light of the following description of particular, non-limiting embodiments of the invention. Brief description of the drawings

[0037] Reference will be made to the attached drawings, among which:

[0038] [Fig-1] [Fig.1] schematically represents an electricity meter and illustrates the calibration of the meter's measurement module;

[0039] [Fig.2] [Fig.2] is a simplified front view of the meter, without the cover that closes the meter box;

[0040] [Fig.3] [Fig.3] is a graph comprising a temperature curve (in °C) of a current transformer winding as a function of time, and a curve of the current (in A) flowing through the winding as a function of time. DETAILED DESCRIPTION

[0041] With reference to figures 1 and 2, the electric meter 1 is here a three-phase meter which is intended to measure the electrical energy supplied to the electrical installation 2 of a subscriber by a distribution network 3.

[0042] The distribution network 3 comprises three phases Ph (Phi, Ph2 and Ph3), and a neutral N.

[0043] Meter 1 includes three input ports Pe each connected to one of the phases Ph of the distribution network 3, and one input port Pe connected to the neutral N. Meter 1 also includes four output ports Ps connected to the installation 2 (three for the phases and one for the neutral).

[0044] The meter 1 comprises three phase conductors 4 each connected to one of the phases Ph, and a neutral conductor 5 connected to the neutral N.

[0045] The meter 1 incorporates a disconnecting device 6 (visible in [Fig. 2]) comprising, for each phase Ph, a switch mounted on the associated phase conductor 4. The disconnecting device 6 is used in particular to remotely disconnect or restore the power supply to the installation 2 in the event, for example, of termination of the subscription or non-compliance with the subscription contract.

[0046] The counter 1 comprises a so-called “application” part and a so-called “metrology” part.

[0047] The application part includes an application microcontroller 7 which, in particular, controls the switching element 6.

[0048] The metrology portion comprises a processing unit 8 (electronic and software). The processing unit 8 includes at least one processing component 9, which is, for example, a general-purpose processor, a processor specializing in signal processing (or DSP, for Digital Signal Processor), a microcontroller, or a programmable logic circuit such as an FPGA (for Field Programmable Gate Array) or an ASIC (for Application-Specific Integrated Circuit). The processing unit 8 also includes one or more memories 10, connected to the processing component 9, or integrated into the processing component 9. At least one of these memories 10 forms a computer-readable storage medium on which is stored at least one computer program comprising instructions that lead the processing unit 8 to execute the steps of the measurement process that will be described below.

[0049] Here, the processing unit 8 includes a metrology microcontroller 9. It is in the metrology microcontroller 9 that the measurement process is implemented.

[0050] In addition to the processing unit 8, the metrology part includes, for each phase Ph of the distribution network 3, a voltage measuring device 11, a current measuring device 12, and a measuring module 14. In [Fig.1], the elements 11, 12, 14 (and their components) are shown for one phase Ph only, but the meter 1 includes such elements for each of the phases Ph.

[0051] The voltage measuring device 11 comprises resistors 15 forming a voltage divider bridge, and a voltage measuring chain 16. The voltage divider bridge produces, from the phase voltage Uph of the phase Ph of the network 3, a voltage less than or equal to 3.3V. The voltage measuring chain 16 includes an analog-to-digital converter. The voltage measuring chain 16 produces measurements of the phase voltage Uph present on the associated phase Ph.

[0052] The current measuring device 12 includes a current transformer 17 and a current measuring chain 18 connected to the current transformer 17.

[0053] The current transformer 17 comprises a primary winding 19, in which the phase current Iph flows, and a secondary winding 20.

[0054] Each winding 19, 20 can comprise any number of turns.

[0055] The primary winding 19 is preferably the phase conductor 4 itself, and therefore in this case comprises a single turn. The transformer 17 is then, for example, an open-circuit current transformer forming a toroid around which the secondary winding is wound in turns all along the toroid through which the phase conductor 4 passes. It can also be a Rogowski coil.

[0056] The current measurement chain 18 preferably comprises a resistor followed by an analog-to-digital converter, connected to the secondary winding 20 of the current transformer 17, and optional additional electronic components which may include one or more amplifiers. The current measurement chain 18 produces initial measurements representative of the current flowing in the primary winding and supplied to the installation 2. This is therefore the phase current Iph flowing on the phase Ph.

[0057] We therefore have in the meter a first current transformer 17a used to measure the first phase current Iphl, a second current transformer 17b used to measure the second phase current Iph2, and a third current transformer 17c used to measure the third phase current Iph3.

[0058] The measuring module 14 is a digital module, which is implemented in the metrology microcontroller 9 of the meter 1. The measuring module 14 is connected to the voltage measurement chain 16 and to the current measurement chain 18.

[0059] The measuring module 14 includes, in the case of fundamental measurements, low-pass filters 22a, 22b arranged to suppress harmonics of the phase voltage and phase current so as to produce a fundamental phase voltage and a fundamental phase current. In the case of measurements with harmonics, the low-pass filters 22a and 22b are removed.

[0060] The measurement module 14 further includes a plurality of calculation modules, which allow the evaluation of the active power, reactive power, RMS voltage (for Root Mean Square; this is the effective value) and RMS current distributed by the distribution network 3 via the phase Ph.

[0061] For each phase Ph, the measurement of these quantities makes it possible to evaluate the electrical energy supplied to the installation 2 by the distribution network 3.

[0062] The measurement module 14 uses a number of calibration parameters to perform these calculations. The calibration parameters are as follows: Ky, Kj, Decal_P, Kv NOISE, Kj NOISE, Kcos NOISE£os((p)' Ksm_NOISEM^

[0063] The phase voltage U is multiplied by a multiplicative factor incorporating the voltage parameter Ky, to obtain a compensated voltage çj'. The multiplicative factor is equal to (1 + K•

[0064] The phase current is multiplied by a multiplicative factor incorporating the current parameter Kj, to obtain a compensated current. The multiplicative factor is equal to (l+ÆJ. JE

[0065] Module 23 acquires the compensated voltage jf and the compensated current J and produces a gross active power P.

[0066] The parameter Decal_Pes\. added to the gross active power / *to obtain an active power p.

[0067] Module 24 acquires the compensated voltage and compensated current l' and produces a gross reactive power Q.

[0068] Module 25, which is in the form of a matrix, acquires the active power P' and the reactive power Q' (here equal to Q) and evaluates the compensated active power p" and the compensated reactive power q", by calculating p" = +Ksin^ = -

[0069] The parameter K^os NOISE^0^)^ added to the compensated active power p' to obtain the active power p"'.

[0070] The parameter KSEy NOlSE-^f^P^^ added to the compensated reactive power g' to obtain the reactive power q”'.

[0071] Module 26 acquires the compensated voltage jj' and calculates the squared RMS voltage: parameter Ky NOISE^ added to the squared RMS voltage, then the square root of The result of this addition is calculated to obtain the compensated RMS voltage.

[0072] Module 27 acquires the compensated current and calculates the squared RMS current parameter Kj no!SEc^ added to the squared RMS current, then the The square root of the result of this addition is calculated to obtain the compensated RMS current ^RMS'

[0073] The calibration parameters used by the measurement module 14 make it possible in particular to compensate for the variations in gain on the phase voltage, due to the components of the voltage measurement chain 16, the variations in gain on the phase current, due to the components of the current measurement chain 18, the effects of the white noise intrinsic to the counter 1, the quantization noises of the analog-to-digital converter of the voltage measurement chain 16 and of the analog-to-digital converter of the current measurement chain 18, the variations in gain of the voltage measurement chain 16 and of the current measurement chain 18, etc.

[0074] The calibration parameters starting with "K" as well as Decal_P are fixed and factory calibrated.

[0075] The calibration parameter A, for its part, makes it possible to compensate for the phase variations of the current measurement chain 18, due to the current transformer 17.

[0076] This is therefore a measurement phase shift produced by the current transformer 17 on the first measurements, which are produced by the current measuring device 12 and which are representative of the phase current Iph supplied to the installation 2 and circulating in the primary winding 19 of the current transformer 17.

[0077] This measured phase shift A is variable and is not factory calibrated. It depends on the temperature of the winding 20 of the current transformer 17.

[0078] The measurement phase shift A is estimated in real time by the processing unit 8 of the counter 1.

[0079] The counter 1 incorporates a temperature sensor 30, which is here an NTC thermistor. The thermistor 30 is connected to the metrology microcontroller 9 of the processing unit 8. The thermistor 30 produces secondary measurements representative of the internal temperature prevailing inside the counter 1.

[0080] For each current transformer 17, the processing unit 8 will therefore evaluate the measurement phase shift A in the following way.

[0081] The processing unit 8 first evaluates an estimated current from the initial measurements (produced by the current measuring device 12), and the Internal temperature Ti prevailing in counter 1 from the second measurements (produced by the thermistor 30).

[0082] Then, a calculation module 40 of the measurement module 14 of the processing unit 8 evaluates an estimated temperature Te of the secondary winding 20 from the estimated current le and the internal temperature Ti. The processing unit 8 then evaluates the measurement phase shift A produced by the current transformer 17 on the first measurements, from the estimated temperature of the secondary winding 20 of the current transformer 17. The measurement phase shift is intended, as we have seen, to be used to measure the electrical energy supplied to the installation 2 by the distribution network 3.

[0083] The measured phase shift A can be deduced from the estimated temperature of the secondary winding 20 from the manufacturer's data for the transformer 17. A lookup table 31 is, for example, stored in one of the memories 10 of the processing unit 8. This lookup table 31 associates phase shift values ​​with temperature values ​​of the secondary winding 20.

[0084] In a first embodiment, the estimated current is the current I corresponding to the first measurements produced by the measuring device 12. The estimated winding temperature is, for example, evaluated from the estimated current squared; an analogy is used with the heat dissipation of a resistor in RI2

[0085] We then have, for example:

[0086] TCl(t)=CTN(f) +KUl(t)2

[0087] TC2 (t} = CTN (t) + K2I?$

[0088] = CTN(t) + K3I^

[0089] where TCT(f) is the estimated (real-time) temperature of the secondary winding 20 of the first transformer 17a of the first phase Phi, / [( / ) is the estimated current for the first transformer 17a, K1 is a fixed factor determined by design, and CTN(t) is the internal temperature,

[0090] where C2(M is the estimated (real-time) temperature of the secondary winding 20 of the second transformer 17b of the second phase Ph2, Ï2(t) is the estimated current for the second transformer 17b, K2 is a fixed factor determined by design, and CTN(t) is the internal temperature,

[0091] and where TC3(t) is the estimated (real-time) temperature of the secondary winding 20 of the third transformer 17c of the third phase Ph3, Z3( / ) is the estimated current for the third transformer 17c, K3 is a fixed factor determined by design, and CTN(t) is the internal temperature.

[0092] Figure 3 shows how the actual temperature T of the secondary winding 20 of a current transformer 17 varies when a phase current Iph, initially zero, then equal to 40A, then equal to 100A, flows in the primary winding 19. This Figure 3 was obtained during self-heating tests of the current transformers 17. A certain delay is required for the winding temperature to reach a constant level corresponding to the applied current step (approximately 40°C for the 40A step, and approximately 112°C for the 100A step).

[0093] In a second embodiment, the estimated current le, from which the measurement phase shift & is evaluated, is no longer directly the current corresponding to the first measurements. This time, to take into account the transient phases, the processing unit 8 applies a low-pass filter 32 to the first measurements to obtain the estimated current le.

[0094] Applying the low-pass filter 32 to the current I(t), whose output is I'(t), smooths the curve to more closely approximate reality, where the winding temperature takes some time to stabilize. The estimated temperature Te, as a function of time, of the secondary winding 20, obtained by this method, is closer to the actual temperature of the winding.

[0095] We therefore obtain:

[0096] ^1( / )= CTN (t)+K

[0097] TC2 ( f} = CTN ( +

[0098] rC3CTN( f )+ K31

[0099] where TCI(t) is the estimated (real-time) temperature of the secondary winding 20 of the first transformer 17a of the first phase Phi, / ']( / ) is the estimated current for the first transformer 17a (first measurements on which the low-pass filter 32 was applied), ^1 is a fixed factor determined by design, and CTN(t) is the internal temperature,

[0100] where TC2(f) is the estimated (real-time) temperature of the secondary winding 20 of the second transformer 17b of the second phase Ph2, / 3( / ) is the estimated current for the second transformer 17b (first measurements on which the low-pass filter 32 was applied), K2 is a fixed factor determined by design, and CTN(t) is the internal temperature,

[0101] where TC3( / ) is the estimated (real-time) temperature of the secondary winding 20 of the third transformer 17c of the third phase Ph3, / 3( / ) is the estimated current for the third transformer 17c (first measurements on which the low-pass filter 32 was applied), K3 is a fixed factor determined by design, and NTC(t) is the internal temperature.

[0102] The low-pass filter 32 used is, for example, a first-order Butterworth filter. We seek to filter l(Z) so as to obtain at the output of the linear filter H(Z)-

[0103] I{Z) = l(Z)H(Z)

[0104] The Z-transform of a first-order Butterworth filter is expressed by the relation:

[0105] H (Z ) = with Z = vl~aZ

[0106] It is assumed that the current I(t) is sampled digitally at a frequency of 1Hz.

[0107] The parameter a is chosen so that the rise time is compatible with the design and the filter gain is equal to 1.

[0108] Here we choose « = 0.9993606 and G = 0.0003197 to have a rise time to 90% of Ih and a gain of 1.

[0109] In a third embodiment, the processing unit 8 evaluates, for each current transformer 17, the estimated temperature Te of the winding 20 of said current transformer 17 from:

[0110] - of the internal temperature Ti (thermistor 30),

[0111] - of the estimated current for said current transformer, and

[0112] - also using an approximate temperature Ta of the secondary winding 20 of at least one other current transformer 17, the approximate temperature Ta of the secondary winding 20 of at least one other current transformer 17 being evaluated from the internal temperature Ti and the estimated current for at least one other current transformer 17.

[0113] In this embodiment, the "approximate temperature" therefore corresponds to the "estimated temperature" of the previous embodiments.

[0114] The at least one other current transformer includes the current transformer positioned closest to said current transformer.

[0115] Here, the electric meter 1 includes a first current transformer 17a, a second current transformer 17b and a third current transformer 17c.

[0116] The transformers 17a, 17b, 17c of phases Phi, Ph2, and Ph3 are aligned in that order. Figure 2 shows the first transformer 17a on the left, the second transformer 17b in the middle of the other two, and the third transformer 17c on the right. The second current transformer 17b is therefore positioned between the first current transformer 17a and the third current transformer 17c.

[0117] It can be considered that the second transformer 17b, when it is traversed by a strong current (at least a few tens of amperes), can raise the temperature in the vicinity of the first transformer 17a and the third transformer 17c.

[0118] The first transformer 17a, when a high current flows through it, can raise the temperature in the vicinity of the second transformer 17b. The third transformer 17c, when a high current flows through it, can also raise the temperature around the second transformer 17b.

[0119] Thus, processing unit 8:

[0120] - evaluates the estimated temperature of the secondary winding 20 of the first current transformer 17a also using the approximate temperature of the secondary winding 20 of the second current transformer 17b;

[0121] - evaluates the estimated temperature of the secondary winding 20 of the second current transformer 17b also using the approximate temperature of the secondary winding 20 of the first current transformer 17a and the approximate temperature of the secondary winding 20 of the third current transformer 17c;

[0122] - evaluates the estimated temperature of the secondary winding 20 of the third current transformer 17c also using the approximate temperature of the secondary winding 20 of the second current transformer 17b.

[0123] Thus, compared with the formulas previously used, the ambient temperature is no longer assessed solely by the value of the temperature measured by the thermistor 30, but rather by a temperature derived from that of the thermistor 30 and those of the transformers 17.

[0124] We therefore continue to estimate the approximate temperatures TC1(t), TC2(t) and TC3(O as before, but we deduce the estimated temperatures (in real time) TC'Ut), TC2(t) and TC'3(t) in the following way.

[0125] In the case of the first transformer 17a, the term CT N ( / ) is replaced in the formula by (CTN {t) + TC2 ( f ) ) / 2 and the estimated temperature TC^t is determined, which is such that:

[0126] Tdçt) = {CTN(t)+TC2(t}]l 2 + K\Tl(tf

[0127] In the case of the second transformer 17b, the term NTC(t) is replaced in the formula by (NTC(¢) + (TC1(t) + TC3( / )) / 2) / 2 and the estimated temperature TC'2(¢) is determined, which is such that:

[0128] TC2(t) = {CTN(t) + (TCl(t) + TC3(t}) / 2) / 2 + K2T2(tf

[0129] In the case of the third transformer 17c, the term NTC(t) is replaced in the formula by (NTC(t) + TC2(t)) / 2 and the compensated temperature TC3(t) is determined such that:

[0130] TC'3(t) = (CTN(t) + TC2(¢)) / 2 + K3T3(tf

[0131] It is then the estimated temperatures TC'(t), TC'2(t) and TC'3(t) that are taken into account to determine the respective measurement phase shifts Ac, 1(t), Ap2(t) and Ap3

[0132] This embodiment is the preferred three-phase embodiment, because it provides the best accuracy.

[0133] The first and second embodiments described apply of course in the case of a single-phase meter. Typically, a single-phase meter includes a single current transformer, used to measure the current flowing on the neutral (the phase current being preferably measured by a shunt).

[0134] The estimated temperature is such that:

[0135] TCN(t)-CTNÇt)+KNJN(t)2

[0136] In this case, the estimated current IN(t) is constant, obtained directly from the first measurements produced by the current measurement device which measures the neutral current.

[0137] Alternatively, and preferably, the estimated temperature is obtained as follows:

[0138] TCN(t^ = CTN(t) +KNrN(tf

[0139] In this case, the estimated current / ^( / )2681 'c current corresponding to the first measurements, on which the low-pass filter 32 was applied.

[0140] We are now interested in the positions of the different elements in counter 1. It is preferable that the thermistor 30 be positioned in the meter box 1 as far away as possible from hot spots, i.e. in this case the current transformer(s) 17 and the switching device 6.

[0141] Thus, advantageously:

[0142] - the current transformer(s) 17 and the switching device 6 are positioned in a first side between a left side and a right side of the electric meter box 1, and in a first part between an upper part 1a and a lower part 1b of the electric meter 1;

[0143] - the thermistor 30 is positioned on a second side and in a second part of the electric meter 1.

[0144] The terms "high", "low", "left", "right" correspond to a situation in which the meter is positioned in its nominal operating position (here, with its rear face positioned against a vertical support).

[0145] The transformer(s) 17 and the switching element 6 are preferably positioned in the lower part 1b of the electric meter 1, for example on the left, and the thermistor 30 is preferably positioned in the upper part la of the electric meter 1, and therefore on the right in this example.

[0146] The current transformer(s) 17 and the switching element 6, on the one hand, and the thermistor 30, on the other hand, are preferably located in diagonally opposite parts of the internal volume of the meter 1.

[0147] In the case where the current transformer(s) 17, the switching element 6 and the thermistor 30 are mounted on the same electrical board, they are located in diagonally opposite parts of said board.

[0148] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0149] The formulas used could be different from those given here.

[0150] For example, the estimated temperature of a transformer winding could be evaluated from the estimated current cubed and not squared.

[0151] It is possible to add coefficients in all formulas.

[0152] For example, we could have:

[0153] TCl(t) ^a.CTNÇtUKUlit)2

[0154] The meter can be a single-phase, three-phase or, more generally, polyphase meter.

[0155] The estimated temperature, from which the measurement phase shift is evaluated, may be the temperature of a primary winding of the current transformer. In this case, the estimated current, used to evaluate the estimated temperature, is evaluated from representative measurements of the current flowing in this primary winding.

Claims

Demands

1. Electricity meter (1), arranged to measure electrical energy supplied to an installation (2) by a distribution network (3), the electricity meter (1) comprising: - a current measuring device (12), comprising a current transformer (17), and arranged to produce first measurements representative of a current (Iph) flowing in a winding (20) of the current transformer; - a temperature sensor (30), arranged to produce second measurements representative of an internal temperature (Ti) prevailing inside the meter; - a processing unit (8) arranged to: • evaluate an estimated current (le) from the first measurements, and the internal temperature (Ti) from the second measurements; • evaluate an estimated temperature (Te) of the winding (20) from the estimated current and the internal temperature;• evaluate, from the estimated temperature, a measurement phase shift (Aç>) produced by the current transformer on the first measurements, the measurement phase shift being intended to be used to measure said electrical energy.;

2. Electric meter according to claim 1, wherein the processing unit (8) is arranged to apply a low-pass filter (32) to the first measurements to obtain the estimated current (the).

3. Electric meter according to claim 2, wherein the low-pass filter (32) is a first-order Butterworth filter.

4. Electric meter according to any one of the preceding claims, wherein the estimated temperature (Te) is evaluated from the estimated current (le) squared.

5. Electricity meter according to any one of the preceding claims, comprising a plurality of current measuring devices (12), each comprising a current transformer (17), the processing unit (8) being arranged, for each current transformer (17), to evaluate the estimated temperature of a winding (20) of said current transformer from: - the internal temperature, - the estimated current for said current transformer, and - also using an approximate temperature of a winding of at least one other current transformer, the approximate temperature of the winding of at least one other current transformer being evaluated from the internal temperature and the estimated current for at least one other current transformer.

6. Electric meter according to claim 5, wherein at least one other current transformer comprises the current transformer positioned closest to said current transformer.

7. Electric meter according to claim 6, wherein the electric meter (1) comprises a first current measuring device including a first current transformer (17a) and arranged to measure a current (Iph1) flowing on a first phase (Phi), a second current measuring device including a second current transformer (17b) and arranged to measure a current (Iph2) flowing on a second phase (Ph2), and a third current measuring device including a third current transformer (17c) and arranged to measure a current (Iph3) flowing on a third phase (Ph3), the second current transformer (17b) being positioned between the first current transformer (17a) and the third current transformer (17c),the processing unit (8) being arranged to: - evaluate the estimated temperature of the winding of the first current transformer (17a) using also the approximate temperature of the winding of the second current transformer (17b); - evaluate the estimated temperature of the winding of the second current transformer (17b) using also the approximate temperature of the winding of the first current transformer (17a) and the approximate temperature of the winding of the third current transformer (17c); - evaluate the estimated temperature of the winding of the third current transformer (17c) using also the temperature, approached the winding of the second current transformer (17b).

8. Electric meter according to any one of claims 1 to 4, the electric meter being a single-phase meter comprising a single current measuring device, including a current transformer and arranged to measure a current flowing on a neutral.

9. Electric meter (1) according to any one of the preceding claims, wherein: - the current transformer(s) are positioned in a first side among a left side and a right side of the electric meter, and in a first part (1b) among an upper part (la) and a lower part (1b) of the electric meter; - the temperature sensor (30) is positioned in a second side and in a second part (la) of the electric meter.

10. A measurement method, implemented in the processing unit (8) of the electric meter (1) according to any one of the preceding claims, and comprising the steps of: • evaluating an estimated current (le) from the first measurements, and the internal temperature (Ti) from the second measurements; • evaluating an estimated temperature (Te) of the winding (20) from the estimated current and the internal temperature; • evaluating, from the estimated temperature, a measurement phase shift (A#>) produced by the current transformer on the first measurements, the measurement phase shift being intended to be used to measure said electrical energy.

11. Computer program comprising instructions that cause the processing unit (8) of the electric meter (1) according to any one of claims 1 to 9 to perform the steps of the measurement method according to claim 10.

12. Computer-readable recording medium on which the computer program according to claim 11 is recorded.

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