AU2010264383A1 - Electricity Meter Having an Uninsulated Current Sensor and a Cutoff Switch - Google Patents

Abstract

The invention relates to an electricity meter for measuring a phase current and a voltage which are used by a user (3) over at least one phase n of an electric power distribution network (1), comprising a metrology portion (2) with an uninsulated current sensor (Rshunt) in series on the phase n conductor for measuring the current of phase Iphn from a measurement mes Vmes of the difference in potential at the terminals of the sensor, a first voltage divider (R4, R5) receiving the phase voltage as an input and outputting a measurement Vphn upstream of a difference in potentials between a first potential given by the conductor and a second potential, and a cutoff contactor (K1) in series with the current sensor. According to the invention, the metrology portion (2) comprises a monitoring device that includes a second voltage divider (R1, R2) connected in parallel on the serial assembly formed by the sensor (Rshunt) and the cutoff contactor (K1), outputting a measurement Vphn upstream/downstream that represents the difference in potential between the phase conductor downstream from the cutoff contactor (K1) and the phase conductor upstream from the metrology portion. The various measurements can be used to detect various situations (pole integrity of the cutoff contactor, fraud by short-circuit, downstream self-generation, resetting the main circuit breaker) when the contactor is open or closed.

Description

1 AN ELECTRICAL ENERGY METER HAVING A NON-ISOLATED CURRENT SENSOR AND A CUTOFF SWITCH The present invention relates to an electricity meter fitted with a monitoring device for monitoring 5 potential differences between a first potential given by a phase (or "live") conductor and a second potential of the meter. The invention is applicable to an electricity meter of the single-phase type, having a single phase conductor 10 and a neutral conductor that gives the second potential. The invention is also applicable to a polyphase electricity meter having n phase conductors, e.g. three phase conductors, and a neutral conductor giving the second potential. 15 Finally, the invention is also applicable to a polyphase electricity meter that does not have a neutral conductor. Under such circumstances, the second potential is internal to the meter. Electrical energy suppliers have recently begun 20 requiring electricity meters to be associated with a switch for cutting off the phase current feed, the switch preferably being located in the metrological enclosure of a meter, so as to make it possible to control the switch remotely by means of the meter. Thus, without requiring 25 maintenance personnel to visit, a supplier may interrupt or re-establish the supply of energy to a user. This makes it possible in particular to manage situations in which the user has not paid an electricity bill or in which a tenant has canceled a subscription and until a 30 new tenant takes out a new subscription. The cutoff switch is generally connected in series in each of the phases n of the distribution network, with the neutral conductor consequently not being interrupted by the switch. When an open command is performed, the 35 electricity meter must monitor potential differences between the network phase and the second potential, e.g. given by the neutral conductor when one is provided, 2 upstream and downstream from the open pole of the cutoff switch. More precisely, when the cutoff switch has been opened, it is necessary to be able to measure the 5 following quantity: Vphn -Vphn - VPhn down-up up down in which equation, for a given phase n, Vph, corresponds UP to the potential difference between the neutral conductor and the phase n on the side of the distribution network 10 (upstream from the meter), and Vow" corresponds to the potential difference between the neutral conductor and the phase on the load side (downstream from the meter and the cutoff switch). The object of this monitoring is to be able to 15 detect various situations that might occur after the cutoff switch has been opened, and to respond accordingly to those situations. A first possible situation relates to user fraud by short-circuiting the cutoff switch, so as to be able to 20 take electricity from the distribution network without it being measured by the meter. Another situation relates to the presence of a self production source downstream from the cutoff switch, for example a generator that the user has installed as a 25 result of distribution being cut off as a result of the cutoff switch being open. Under such circumstances, any closure of the cutoff switch would run the risk of setting up a short circuit, thereby damaging items such as the meter and the self-production source. Thus, prior 30 to validating any command to re-engage the cutoff switch, it is essential for the meter to ensure beforehand that no self-production source is present. Another situation relates to an additional requirement whereby an order to re-engage the cutoff 35 switch should be validated only following a voluntary action by the user on the main circuit breaker. Under such circumstances, prior to the meter actually causing 3 the cutoff switch to close, it must begin by detecting manual re-engagement of the main circuit breaker. Furthermore, it may also be necessary to monitor the quantity Vownu in the event of the cutoff switch being in 5 the closed position, in order to detect an abnormal rise in the contact resistance of the cutoff switch due to a degradation in the surface state of the poles of the switch, which rise could endanger the integrity of the meter and of the electrical installation as a result of 10 the poles heating up excessively. Certain known meters make use of an isolated current sensor that is associated with processing electronics using the neutral of the network as a reference potential. This applies in particular to meters in which 15 the current sensors used are current transformers, or inductive sensors, or active sensors of the Hall effect type, or magnetic field sensors. For meters of those types, the voltages VP" and VP" down UP are measured via two resistor bridges placed respectively 20 between the phase conductor and the neutral conductor upstream from the cutoff switch, and between the phase conductor and the neutral conductor downstream from the cutoff switch. Each of these resistor bridges delivers signals that are referenced to neutral potential, and 25 each of them attenuates the voltages between phase and neutral to amplitudes that are compatible with the input levels of analog-to-digital converters. It is easy both to detect fraud by short-circuiting the shunt and the cutoff switch, and to detect the 30 presence of self-production downstream from the cutoff switch, by comparing the amplitudes and phases of the upstream and downstream voltage measurements. In order to detect a user operating the main circuit breaker, a high-value resistance is connected in parallel 35 with the power contact of the cutoff switch so as to generate a potential difference across the terminals of the resistor bridge measuring the downstream voltage, 4 which voltage is greatly influenced by the equivalent impedance of downstream load, in particular a load of very high resistance when the poles of the (single pole or two pole) circuit breaker are open, or of smaller 5 resistance when said circuit breaker is closed to connect with a residual downstream load. Nevertheless, there is no present-day solution that makes equivalent monitoring possible for electricity meters that use a non-isolated current sensor, e.g. a 10 resistive or shunt type sensor. However, such a sensor presents advantages in terms of being immune to the fraud involving the use of a permanent magnet, and it is also relatively insensitive to alternating magnetic fields. An object of the present invention is to mitigate 15 the above limitations by proposing a device for monitoring potential differences between a first potential given by a phase conductor and a second potential in an electricity meter for residential use that has both a non-isolated current sensor and also a 20 cutoff switch on each of the phases of the meter. More precisely, the invention provides an electrical energy meter for measuring a phase current Iphn and a phase voltage Uphn as consumed by a user installation from at least one phase n of an electricity distribution 25 network, the meter being of the type including a metrological portion in which the reference potential is constituted by said phase n, said metrological portion including: a non-isolated current sensor in series with the conductor of phase n in order to measure the phase 30 current Iphn by measuring the potential difference Vmes across the terminals of said sensor; a cutoff switch in series with said current sensor; and a monitoring device suitable for delivering a measurement dow"-_ representative of the potential difference between the phase conductor 35 downstream from the cutoff switch and the phase conductor upstream from the metrological portion, the meter being characterized in that the metrological portion further 5 includes a first voltage divider receiving as input said phase voltage Uphf and delivering a measurement of a potential difference VP" between a first potential given UP by the phase conductor and a second potential, in that 5 the monitoring device includes both a second voltage divider connected in parallel with the series connection formed by the current sensor and the cutoff switch, and a resistor connected between the phase conductor and the second potential downstream from the cutoff switch, and 10 in that the user installation includes a main circuit breaker and the meter includes means for acting when the cutoff switch and the main circuit breaker are both in the open position to detect a transition in the measurement VPh" between a first value equal to aixVphn down-up UP 15 and a second value equal to a 2 xVuh", which values are representative respectively of the position of the main circuit breaker performing a transition between a closed state to an open state and the position of the main circuit breaker forming a transition between an open 20 state and a closed state. The meter may then advantageously include means for authorizing a request to close the cutoff switch when said transition has been detected, and means for refusing a request to close the cutoff switch, otherwise. 25 In a particular embodiment, the second potential is given by a neutral conductor. In a variant, the second potential is internal to the meter. In a preferred embodiment, when the cutoff switch is 30 in a closed position, the meter includes means for calculating a coefficient representative of active losses in the cutoff switch and the current sensor from measurements of the potential difference Vnes across the terminals of said sensor and measurements Vph" down- up 35 representative of the potential difference between the phase conductor downstream from the cutoff switch and the phase conductor upstream from the metrological portion, 6 and monitoring means for monitoring the drift of said coefficient relative to a predetermined threshold in order to detect an abnormal rise in the contact resistance of the cutoff switch. 5 Means then advantageously cause the cutoff switch to open if the drift of said coefficient exceeds said predetermined threshold. When the cutoff switch is in an open position, the meter preferably includes monitoring means for monitoring 10 whether the measurement VP", goes below a low threshold corresponding to a percentage of the measurement VfPg", and where appropriate means for generating a fraud alert. When the cutoff switch is in the open position, the meter also preferably includes means for calculating a 15 voltage signal representative of a self-production source downstream from the cutoff switch from the measurements Vph" and Vp",, monitoring means for monitoring both UP down-up'I whether the phase of said voltage signal is different from the phase of V1 and whether the amplitude of said 20 voltage signal crosses a given amplitude percentage of the input signal from the distribution network, typically 70% of V1, and means for refusing a request to close the cutoff switch, where appropriate. The invention can be better understood in the light 25 of the following description made with reference to the accompanying figures, in which: - Figure 1 is an electrical schematic showing the connection of the metrological portion of an electricity meter fitted with the monitoring device of the invention 30 for one phase n of an electricity meter; - Figure 2 is an equivalent electrical schematic in the event of a fraud by short-circuiting the cutoff switch; - Figure 3 is an equivalent electrical schematic in 35 the event of there being a self-generation source present downstream from the cutoff switch; and 7 Figure 4 is a simplified flow chart summarizing the signal processing performed by the electrical energy meter in accordance with the invention for the various detections. 5 Figure 1 is in the form of three functional blocks, showing the connection of one phase n of an electricity meter to a non-isolated electricity sensor in an electricity distribution network. More precisely, the block 1 represents the electricity distribution network 10 for the phase n, the block 2 represents the metrological portion of the electricity meter suitable for measuring current and voltage on the phase n of the network, and the block 3 represents the load downstream from the metrological portion, i.e. the electrical installation of 15 the user. The electricity distribution network of block 1 is equivalent to a power source delivering a voltage Uphm between the phase conductor n and the neutral conductor, together with a phase current Ipm. In Figure 1, the 20 voltage Uphm is represented by -V1. The load 3 downstream from the metrological portion 2 of the meter is made up of a circuit baker K2 that is the circuit breaker on the user's premises and a load in series therewith and represented by its resistance 25 Rload. For each phase n under consideration, where n may be equal to 1, the metrological portion 2 of the meter has a non-isolated sensor for measuring the phase current Imm, typically a shunt resistor Rshuft made of an alloy that 30 presents a very small coefficient of resistivity variation as a function of temperature (e.g. made of Manganin). The input phase to the metrological portion 2 of the electricity meter is the reference potential (0 volts) of 35 the metrological portion. Such a non-isolated measurement sensor, associated with a series connection of resistors R4 and R5 forming a 8 voltage divider that receives the phase voltage Uphf as input suffices to enable the meter to perform its metrological measurements, i.e.: firstly to measure the phase current Iphn by 5 applying Ohm's law as follows: mes=-Rshunt X Iphn (1) where Vmes is the potential difference measured across the terminals of the shunt resistor, the phase input constituting the voltage reference; and 10 - secondly, measuring the phase voltage Uphn using the following equation: VPhn = U x R4 -V x R4(2) U p* (R4 + R5) (R4 + R5) where VPn is equal to the measured potential difference between the neutral conductor and phase n on the 15 distribution network side, i.e. upstream from the metrological portion 2. For each phase under consideration, the metrological portion 2 also includes a cutoff switch Kl in series with the shunt resistor, and downstream therefrom, the pole of 20 the switch being equivalent to a very high resistance (more than 5 megohms (M9) ) when the pole is open and to a resistance that is very low (less than 500 microhms (pQ)) when the pole is closed. The monitoring device of the invention includes two 25 resistors R1 and R2 in series forming a second voltage divider across the terminals of the series connection constituted by the shunt resistor and the cutoff switch K1. The presence of this second voltage divider makes it possible to measure the potential difference between the 30 phase conductor downstream from the pole of the cutoff switch Kl and the metrological reference potential that is constituted in this example by the potential of the phase conductor upstream from the metrological portion, which may be expressed by the following equation: 35 V X R1 (3) 35Vdown -u pole (R1 + R2) 9 where VPl, is the voltage across the terminals of the series connection formed by the shunt resistor and the cutoff switch. Advantageously, the monitoring device also includes 5 a resistor R3 that is connected between the phase conductor and the neutral conductor downstream from the cutoff switch. This resistor R3 serves, by default, to establish at least some minimum admittance downstream from the switch pole. 10 In a possible but non-limiting embodiment of the invention, the following resistances may be selected: R1 = R4 = Ra = 866 ohms (Q) and R3 = R5 = R2 = Rb = 960 kilohms (kQ). There follows a description of how this monitoring 15 device is used to detect the various situations explained in the introduction. Attention is given initially to the normal operation of the electricity meter, in which the cutoff switch K1 and the main circuit breaker K2 are both closed. As 20 mentioned above, the monitoring device fitted to the meter in accordance with the invention is also capable of being used to detect an abnormal rise in the contact resistance RKl (see Figure 1) . When in the closed position, the pole of the cutoff 25 switch K1 is equivalent to a very low resistance (Ra 1 is less than 500 pQ), with this resistance giving rise to continuous active losses that contribute to raising the temperature of the meter. Above equation 3 may also be written in the 30 following form: Vphn =Rhft+R)xi Ri down-up = -(RIun, + Rpn) x +n x R2) (3a) which, on being combined with equation 1, gives: Vphn - (Rhunt + RK1) x V x R (3b) down-up Rshunt mes (R1 + R2) 10 The two measurements Vmes and VP" are of small down-up amplitudes. The sensitivity for the current measurement channel is 150 microvolts per amp (pV/A) for a resistor Rshunt having a resistance of 150 pQ, and the sensitivity 5 at the terminals of the sensor and cutoff switch series connection is 0.585 pV/A if R1 has a resistance of 866 Q and R2 has a resistance of 960 kQ. To process these two measurements, provision is thus made to amplify them by amplifiers of programmable gain. 10 From these two measurements as amplified in this way, it is possible to extract information that is representative solely of the active losses in the two resistances, by calculating the mean value over a given period, e.g. one second, of the product of these two amplified 15 measurements, i.e.: G1 x G2 x Rshunt x (Rshunt + R KI ) x Iphn where G 1 and G 2 are the amplification gains applied respectively to the two measurements. The square root of the resulting mean value divided 20 by the root mean square (rms) value of the voltage drop across the terminals of the shunt resistor gives a coefficient C that includes the ratio of the two resistances, i.e.: C= 1+ RKI Rshunt 25 When using the following resistance values: RKl = 300 pQ and Rshunt = 150 pQ this coefficient has a value of 3 and an active power of 2 watts (W) is dissipated in the pole of the cutoff switch for an rms current of 82 amps (A). 30 Assume for the moment that the resistance of the cutoff switch drifts from 300 pfl to 3000 pQ. The coefficient C then rises to 21, and an active power of 20 W is dissipated, for the same rms current of 82 A, which is not acceptable inside the meter housing, where 11 dissipating an active power of 20 W would give rise to a very great temperature rise within the meter. Monitoring thus consists in using the two measurements Vnes and VP"_ to verify that the drift AC in 5 the above coefficient C does not exceed a certain threshold (e.g. 200%). When this threshold is exceeded, the meter must imperatively cause the cutoff switch K1 to open. An alarm may also be triggered, and relayed by the electricity meter to a centralized system of the 10 distribution network by communication via a concentrator, e.g. communication via carrier currents. Consideration is given below to the situation in which the cutoff switch K1 is in the open position. Figure 2 is an equivalent electrical schematic 15 illustrating a fraud that consists in establishing a short circuit around the cutoff switch Kl. Under such circumstances, it suffices to measure the two voltages VP an down-up and to compare the values as obtained in this way. A fraud situation on a phase n 20 is considered as being detected in the event of the voltage dow"-_p is less than a low threshold corresponding to a percentage X% of Vufpl and having a value of the order of 2%. Thus, by way of example: 25 if Vphn = 230 volts (V), then the corresponding low UP threshold is set at 4.6 Vrms. Monitoring thus consists in using the two measurements Vph" and Vph, to verify that the voltage UP down-up riytathvoag dow"-_p does not drop below a low threshold corresponding 30 to a predefined percentage X% of Vph". Otherwise, the UP meter must produce an alarm that is relayed by the electricity meter to the centralized system of the distribution network by communication via a concentrator, e.g. communication via carrier current in order to inform 35 it about the fraud. Figure 3 is an equivalent electrical schematic illustrating the presence of a self-production source 12 downstream from the cutoff switch, which source is represented by the reference V2. The self-production source thus generates a potential difference V2 between the phase conductor and the neutral conductor downstream 5 from the metrological portion 2, which potential difference differs in amplitude and phase from that of the power source V1. Once more it suffices to measure the two voltages VP and Vou in order to determine this potential 10 difference V2 very accurately. The voltage Vdo"_ is then no longer zero, but is given by the following equation: Vphn = -R1 Vn- (R1+ R x (V2 - V1) (4) such that the voltage V2 can be determined very 15 accurately by applying the following equation (combining above equations 2 and 4): V2 =-(R4 + R5) Vphf + (R1 + R2) Vphn (5) R4 upR1 down-up() This equation may be simplified using the following equation: 20 V\don- Vphn (6) 20 V2 = g x (V d"w_- p V where (Ra+ Rb) Ra in the advantageous special case of: R1 = R4 = Ra and R5 = R2 = Rb 25 It is considered that a situation in which a self production source is present on a phase n has been detected when: - the voltage V2 calculated from above equations 5 or 6 presents a phase that differs from the voltage V1. 30 Under such circumstances, it suffices to provide means for detecting zero crossings of the signal and to deduce the phase of the signal therefrom; and 13 the amplitude of the voltage V2 calculated from above equations 5 or 6 is greater than a given percentage Y% of the amplitude of Vl, typically 70% of V1. Monitoring thus consists here in making use of the 5 two measurements VPh" and VPh_ and verifying whether the UP dow..n-up voltage V2 calculated from equations 5 and 6 satisfies the above two conditions in terms of phase and amplitude. If it does, the internal program of the meter must ensure that no command to close the cutoff switch K1 is 10 authorized. As mentioned above, there may also exist an additional requirement whereby an order to re-engage the cutoff switch K1 is not to be validated without the user taking voluntary action on the main circuit breaker K2. 15 Under such circumstances, prior to the meter actually causing the cutoff switch to close, it is necessary beforehand to detect a manual re-engagement sequence on the main circuit breaker K2. The measurements of the two voltages VPn and Vdo"n-_p as delivered by the monitoring 20 device also enable this detection to be performed. Under such circumstances, firstly the two measured voltages have the same phase and the same frequency, since both voltages come from the same power source V1, and secondly the measured voltage Vhn is a fraction of down-up 25 the measured voltage Vphn, this fraction being influenced directly by the internal resistance of the meter placed between phase and neutral downstream from the switch, by the downstream impedance Rdown of the block 3, and by the open or closed state of the main circuit breaker K2. 30 More precisely, the measured voltage Vdon-p may be expressed in the following form: V p_ = R 3 X Vl (7) Rl + R2 + R 0"" R3 + Rdown i.e., on replacing V1 by its value as determined by equation 2 above: 14 phn R1 X(R4 + R5) Xvphn down-up R + R2 + R3 x Rdow R4 " R3 + RdOWf with Rdowf = RK2 + Rload when the circuit breaker K2 is in the open state and Rdowl .= Rload when the circuit breaker K2 in the closed state. 5 The order of magnitude of Rload should be compared with a resistance of 10 kQ consuming 5.3 W at 230 V. The resistance RK 2 opposed by the circuit breaker K2 when it is open means that the downstream impedance becomes greater than 3 M9. 10 Thus, prior detection of re-engagement of the circuit breaker K2 is based on detecting a transition between two values of Vph, relative to Vphn. down-up UP As a numerically worked example, the following may apply: 15 when the circuit breaker K2 is open: VPhn =a xVp down-up = up where al is close to 0.5 on the assumption that R3 = R2 = R5; - when the circuit breaker K2 is closed and some 20 minimum load remains connected downstream from the circuit breaker K2: Vphn pVph down-up = a 2 Up where a 2 is close to 0.9 assuming that R3 = R2 = R5 and Rdown = 0.1xR3. 25 In a preferred embodiment, detecting a transition between the following two states: state 1: Vp"_ = 50% x Vph" with a tolerance of ±10% down-up UP and state 2: Vp'"_ = 90% x VPh" with a tolerance of down-up UP 30 (-30%, +5%) is interpreted as re-engagement of the main circuit breaker K2 (sequence comprising open state following by closed state). This detection could be used to validate an order to 35 re-engage the cutoff switch Kl. Making the re-engagement 15 function secure could advantageously be achieved by detecting n transitions between states 1 and 2 during a limited interval of time beginning after the first detection of a transition from state 1 to state 2, or a 5 transition from state 2 to state 1. This detection can thus be used to validate an order to re-engage the cutoff switch K1 in identical manner by detecting one, or preferably n, transition(s) from state 1 to state 2 or from state 2 to state 1 during a 10 predetermined time interval. By way of non-limiting example, the number of transitions may be set at 3 over a time interval of 6 seconds. The various above-described detections are preferably implemented by digital signal processor means 15 specific to the meter and that are described with reference to Figure 4. The various measurements Vmes, Vph" and Vdhn-_p as taken for a phase n for the metrological portion 2 of the meter and its monitoring device are digitized by sampling 20 means (not shown) so as to be delivered to a digital signal processor block 4. Prior to being digitized, the signals are preferably amplified as explained above. The digital processor block 4 comprises a signal processor, typically a microcontroller 40, that makes use 25 of particular software routines for performing the various processing steps. It is the same microcontroller 40 that manages the open and closed commands for the cutoff switch Kl on request from the distribution network. The basic processing performed by the meter, 30 i.e. extracting the power consumed (with Kl and K2 closed) from the measurement Vmes and VUPh is not shown in Figure 4. In Figure 4, reference 41 is the software routine that implements detection of an abnormally high contact 35 resistance in the cutoff switch Kl. This routine is performed periodically during stages in which the meter 16 is in operation, i.e. when the cutoff switch Kl and the main circuit breaker K2 are both in the closed state. As explained above, this routine 41 acts in a step or subroutine 410 to calculate the coefficient C that can be 5 expressed as a function Fl of the measurements Vnes and Vhfl",, and also as a function of the ratio RK1/Rehunt. The routine 41 then monitors (step or subroutine 411) the drift AC in this coefficient C relative to a predetermined threshold (e.g. 200%). If this threshold 10 is reached, the routine 41 acts in a step or subroutine 412 to cause the cutoff switch K1 to open, with the meter then being capable via suitable communications means (line carrier currents or radiofrequency) of signaling this failure of the meter member to a central supervision 15 unit. The other detections are all performed when the cutoff switch K1 has been previously placed in the open position. The software routine referenced 42 is the routine 20 that is launched first in order to detect a potential fraud of short-circuiting the meter. This routine acts in step or subroutine 420 to monitor whether the measurement of Vdw"-_ goes below a low threshold corresponding to a percentage X% of the measurement Vphn. UP 25 Where appropriate, a fraud alert is generated (step or subroutine 421) and forwarded by the meter using appropriate communications means (line carrier currents or radiofrequency) to a central supervision unit. Otherwise, a software routine 43 is executed for 30 detecting the presence of a self-production source, if any. This routine acts in a step or subroutine 430 to calculate the voltage signal V2 generated by such a source, which may be expressed as a function F2 of the measurements Vph" and Vh", (see above-mentioned equation UP down-up aoemnindeuto 17 5 or 6). The routine 43 then acts in step or subroutine 431 to monitor whether the phase of this voltage signal V2 differs from the phase of V1, and whether the amplitude of this voltage signal V2 crosses a given 5 percentage Y% of the amplitude of V1, typically 70% of V1. Where appropriate, any request to close the cutoff switch K1 should be refused in a step or subroutine 432. Signaling may be forwarded by the meter using appropriate communications means (line carrier currents or 10 radiofrequency) to a central supervision unit. Otherwise, and if the monitoring device includes the above-described resistor R3, a software routine 44 may be executed to detect re-engagement of the circuit breaker K2. This routine acts in a step or subroutine 440 to 15 detect the measurement VPj"_ presenting a transition from a first value equal to alxVPh" to a second value equal to a 2 xVPh", or vice versa, and prevents any closure of the cutoff switch K1 so long as such a transition has not been detected (step or subroutine 442), or has not been 20 analyzed in application of a deterministic sequence stored in the meter. Otherwise, any request to close the cutoff switch K1 forwarded to the meter by other appropriate communications means (line carrier currents or radiofrequency) may be authorized (step or subroutine 25 441). By means of the invention, it is possible with an electricity meter that uses a non-isolated current sensor in series with a cutoff switch, firstly to monitor the integrity of the power pole of the cutoff switch, and 30 secondly to detect three special situations (short circuit fraud, downstream self-production, re-engagement of the main circuit breaker) while the pole of the switch integrated in the meter is open. For a polyphase meter having non-isolated current 35 sensors of the shunt type, the various measurements should be performed on each of the phases of the meter.

18 The four detections described above give rise to a very small additional cost associated to adding three measurement resistors (R1, R2, R3), with the essential part of the processing being performed by the 5 metrological software. Naturally, the invention also covers circumstances in which fewer than the four above described detections are implemented. In addition, the order of the routines as described above need not be sequential, it being possible for the routines to be 10 executed independently of one another and/or in a different order, even though the above-described sequence has the non-negligible advantage of optimizing processing time and of avoiding useless calculations.

Claims (8)

1. An electrical energy meter for measuring a phase current Iphn and a phase voltage Uphm as consumed by a user installation (3) from at least one phase n of an 5 electricity distribution network (1), the meter being of the type including a metrological portion (2) in which the reference potential is constituted by said phase n, said metrological portion including: a non-isolated current sensor (Rshuft) in series with the conductor of 10 phase n in order to measure the phase current Iphn by measuring the potential difference Vnes across the terminals of said sensor; a cutoff switch (Ki) in series with said current sensor; and a monitoring device suitable for delivering a measurement Vhnu 15 representative of the potential difference between the phase conductor downstream from the cutoff switch (Kl) and the phase conductor upstream from the metrological portion, the meter being characterized in that the metrological portion further includes a first voltage 20 divider (R4, R5) receiving as input said phase voltage Uphm and delivering a measurement of a potential difference Vph" between a first potential given by the phase conductor and a second potential, in that the monitoring device includes both a second voltage divider 25 (Ri, R2) connected in parallel with the series connection formed by the current sensor (Rshuft) and the cutoff switch (Ki), and a resistor (R3) connected between the phase conductor and the second potential downstream from the cutoff switch (Kl), and in that the user installation 30 includes a main circuit breaker (K2) and the meter includes means (40, 440) for acting when the cutoff switch (K1) and the main circuit breaker (K2) are both in the open position to detect a transition in the measurement VPl" between a first value equal to alxV h 35 and a second value equal to a 2 xV h", which values are representative respectively of the position of the main circuit breaker (K2) performing a transition between a 20 closed state to an open state and the position of the main circuit breaker (K2) forming a transition between an open state and a closed state. 5

2. An electrical energy meter according to claim 1, characterized in that it includes means (40, 441) for authorizing a request to close the cutoff switch (K1) when said transition has been detected, and means (40, 442) for refusing a request to close the cutoff switch 10 (K1), otherwise.

3. An electrical energy meter according to any preceding claim, characterized in that the second potential is given by a neutral conductor. 15

4. An electrical energy meter according to claim 1 or claim 2, characterized in that the second potential is internal to the meter. 20

5. An electrical energy meter according to any preceding claim, characterized in that, when the cutoff switch (K1) is in a closed position, it includes means (40, 410) for calculating a coefficient (C) representative of active losses in the cutoff switch (K1) and the current sensor 25 (Rshunt) from measurements of the potential difference Vnes across the terminals of said sensor and measurements down-up representative of the potential difference between the phase conductor downstream from the cutoff switch (K1) and the phase conductor upstream from the 30 metrological portion, and monitoring means (411) for monitoring the drift of said coefficient relative to a predetermined threshold in order to detect an abnormal rise in the contact resistance of the cutoff switch (K1). 35

6. An electrical energy meter according to claim 5, characterized in that it includes means (40, 412) for causing the cutoff switch (K1) to open if the drift of 21 said coefficient (C) exceeds said predetermined threshold.

7. An electrical energy meter according to any preceding 5 claim, characterized in that, when the cutoff switch (K1) is in an open position, it includes monitoring means (40, 420) for monitoring whether the measurement ,_P goes below a low threshold corresponding to a percentage of the measurement VPh , and where appropriate, means (40, 10 421) for generating a fraud alert.

8. An electrical energy meter according to any preceding claim, characterized in that, when the cutoff switch (K1) is in the open position, it includes means (40, 430) for 15 calculating a voltage signal (V2) representative of a self-production source downstream from the cutoff switch (Kl) from the measurements VP and Vhn_,, mon means (40, 431) for monitoring both whether the phase of said voltage signal (V2) is different from the phase of 20 V1 and whether the amplitude of said voltage signal (V2) crosses a given amplitude percentage of the input signal from the distribution network, typically 70% of Vl, and means (40, 432) for refusing a request to close the cutoff switch (Kl), where appropriate.