Field of the Invention

The present invention relates to electricity meters such as Watt-hour meters, and relates, in particular, to industrial and domestic electricity meters for alternating current (a.c.) electrical power supplies operable to continue to perform despite occurrence of certain fraudulent acts.

Background to the Invention Electrical power is the product of voltage and current. An electricity meter may be used to measure the energy consumed from a supply and does this by integrating the instantaneous power over time. A typical meter therefore measures the instantaneous power, being the product of measured voltage and measured current and accumulates this over time whereby to provide the information for the consumed energy. Typically, an electricity meter is connected to the live and neutral voltage connections of an electricity supply, comprising an alternating current source. Similar principles apply in the case of direct current (d.c.) electricity. A load is connected to the meter in such a way that the current flowing from the source to the load can be measured together with the voltage applied across the load.

Electricity meters are susceptible to fraud in many ways since electricity supply companies determine substantially most of their revenue from metered supplies. Prepayment electricity meters where coins are fed into a box associated with the meter have been known for a considerable time and have provided a great temptation to many as a chance to obtain either money and electricity - or both - and a great number of methods for defeating fraud have been achieved, but this teaching does not address such issues. Induction meters basically work with an induction disc turning (as in a Ferraris meter) by action of two electromagnetic fields generated in respective potential and current coils. The most common deceptive method is disconnection of the potential coil, preventing the power torque in the induction disc from being generated. In another common method of defrauding an electricity meter of the induction disc type is to slow down the rotating disc by external means, such as use of a piece of wire arranged to bear on the disc or use of a powerful magnet. Thus, consumptions are neither totalled in the mechanical integrator of

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the meter nor are computation signals made in the digital connection, However, with the advent of electronic meters, for example of the kind described and claimed in U.S. Pat. No. 4,359,684, this method of fraud will no longer be possible.

Nevertheless, there are other, perhaps less obvious, methods of attempting fraud.

In the electronic measurement of watts-hour and similar meters using conventional induction meters of the kind provided with an electronic circuit feeding digital data for computation, centralisation, tele-metering and the like, it is necessary to establish means to detect a possible fraud due to a manipulation of the meter electrical connections.

Some solutions have direct connection to the electricity mains whereby to monitor voltage, but are inconvenient in that these circuits must be protected from strong over- voltages which might be present from time to time in electricity mains and that meters must also be capable of withstanding without impairment of function. The protective elements lead to a notable increase in the cost of these circuits and also reduce the useful life of the equipment or require maintenance tasks unacceptable in this kind of application. In EP0589817, to Ampera SA, an antifraud device in electronic electricity meters is disclosed, which device operates to detect fraud due to manipulations of electrical input and output connections of the meter with respect to the electricity mains. In particular, this teaching seeks to provide a method of determining fraud where disconnection of a voltage coil of the meter has occurred. This teaching provides a Hall sensor associated with the measurement coil and is connected to a rotation sensor of an induction disc within a meter, the necessary means being further provided for the supply of the data fed by the Hall sensor as to the status of the potential coil.

Another common method of defrauding an electricity meter is to connect an external shunt in parallel with the meter. More specifically, the external shunt is connected in parallel with the live wire of the power distribution circuit in which the meter is connected, i.e. the wire in which the current sensor of the meter is connected, so that at least some of the current used by the consumer bypasses the meter and therefore does not contribute to the energy measurement effected by the meter. This method of fraud can be used with both electromechanical and electronic meters, and EP0085769, to Schlumberger Electronics UK, provides an electricity meter for metering the amount of

electrical energy supplied by a supplier to a consumer which meter is provided with means for detecting the presence of an external shunt which has been connected to by-pass its internal current sensing means. The detecting means comprises a step-up auto transformer having its primary winding connected to receive the supply voltage and its secondary winding connected in series with the current sensing means of the meter.

In a typical wiring application, the neutral voltage connection is at approximately the same voltage potential as the earth connection, which provides a "safety connection". In a typical fraud application, the neutral current returning from the load would be connected directly into earth, thus maintaining the voltage across the load. If the consumer removes the neutral connection from the electricity meter, then they often leave connected the live supply and the current flowing from the supplier to the consumer will still pass through the electricity meter. The reason that this connection may be retained is that there is a certain danger of electric shock regarding the removal of the live connection.

Object of the Invention

Therefore, the present invention seeks to provide an improved meter. In particular the present invention seeks to provide a method of detecting manipulation of the electrical connections within the meter. The present invention also seeks to provide a meter having specific circuitry operable to determine correct connection of the meter terminals in order to increase a likelihood of detection of fraud and/or reduce the occurrence of fraud.

Statement of Invention

In accordance with a first aspect of the invention, there is provided an electricity meter, for measuring the amount of electrical energy supplied by an electrical power supplier to an electrical power consumer via an electrical power distribution circuit consisting of at least two electrical supply leads and a safety lead, the meter comprising: current sensing means for sensing the current flowing in at least one of the electrical supply leads, and;

voltage sensing means for sensing the voltage flowing across a measurement load and means responsive to the current sensing means and voltage sensing means sensed by the current sensing means for deriving the energy measurement; wherein the meter is provided with an internal power supply whereby the measurement circuitry can remain actively powered in the event of a fraud where the voltage sensor is disabled, such that current measurement can take place and whereby relative measurement of power can be determined by use of a representative voltage value.

The meter would thus be able to have its circuitry actively powered despite no mains voltage being supplied to the measurement circuitry whereby current flow through the meter could still be determined.

Conveniently, detection means are provided for detecting attempts to fraudulently by-pass the meter, said fraud detection means being operable to produce a signal indicative of such an attempt when the resistive component of the difference between the respective currents flowing to and from the consumer via the meter exceeds a predetermined value. Upon removal of power from the electricity supply to the measurement circuitry, the back-up secondary power supply, conveniently being a battery of dry-electrical cells, is employed to power the measurement supply. Alternatively the power supply could comprises rechargeable cells and utilises induced voltage obtained from the current meter supply cable to provide, under ordinary operating conditions, a trickle charge current. Alternatively or additionally, the secondary meter determines current readings at given intervals continuously, whereby comparative data and thus consumption can be determined.

The present invention provides a method whereby electrical power consumption may be detected and measured, when a neutral terminal has been disconnected from the meter and the live connections remain connected (when the current measurement apparatus monitors current passing through the live terminal or vice versa, as appropriate). The measurement accuracy will be reduced compared to non-fraud measurement conditions.

If the circuitry is able to measure the current in the live circuit, then it is possible for it to make use of a fixed or default value for the instantaneous voltage. In this way

(although the meter is no longer strictly accurate) it is able to calculate a value for the instantaneous power. The default value for instantaneous voltage may be taken as a punitive value, whereby to discourage fraud.

The circuit can be operated so that it is constantly measuring the current in the current measurement circuit, or it could be operated so that it makes periodic or random measurements of the current.

This invention relates to a method of detecting this fraud attempt using an electricity meter with using electronic circuitry. To do this the meter is fitted with a battery that so that the measurement circuitry remains actively powered even though the mains ac. voltage may no longer be available due to a non-current measured supply of a two wire supply to the meter having been removed.

In this way, the meter would be able to continue power measurements if the non- current measurement path terminals of the meter had been removed.

Brief Description of the Figures

For a better understanding of the present invention, reference will now be made, by way of example only, to the Figures as shown in the accompanying drawing sheets, wherein:

Figure 1 illustrates a typical method of metering a supply of electricity; Figure 2 illustrates a fraudulent use of the metering method depicted in Figure 1 ; and,

Figure 3 illustrates a meter in accordance with the present invention.

Detailed description of the Preferred Embodiments

There will now be described, by way of example only, the best mode contemplated by the inventor for carrying out the present invention. In the following description, numerous specific details are set out in order to provide a complete understanding to the

present invention, It will be apparent to those skilled in the art, that the present invention may be put into practice with variations of the specific.

Each domestic electrical power distribution circuit typically comprises of a live wire and a neutral wire having a typical voltage of 220 to 240 volts a.c. at 50 Hz, therebetween. With reference to Figure I ₁ there is shown a typical meter installation, 10, for a single phase domestic application, where an electrical source, 12, is provided with live and neutral terminals, 14, 16, which lead directly to a meter, 18, at each premises supplied with electricity. Such a meter, 18, is placed between the electricity supply and cabling within the premises for electrical fittings, and has input terminals for livein and neutraljn respectively, 20 & 22, and output terminals for live _ou t and neutraLt respectively, 24 & 26. The current is measured passing through the live conductor and the voltage is measured across the load, 28, which is connected between the livβm and neutral^ terminals. A safety earth cable, 30, is shown, which runs in parallel with the live and neutral cables. Typically the earth cable is connected to the neutral potential.

Fraudulent use of such arrangements can take place when one or other of the neutral terminals, 22, 26 is removed or the neutral cabling is effectively discarded, and the earth cable is employed as an assumed neutral cable, as shown in Figure 2. Since the meter is effectively able to measure only current, it cannot meter the energy flowing through to the consumer. As will be appreciated, if the instantaneous voltage is determined as being zero, then the instantaneous power would also be determined as being zero. Thus a simple method of defrauding an electricity supply company can be effected by the simple expedient of removing the neutral connection from the input supply.

Modern meters are typically provided with circuitry within a sealed housing made from a suitable electrically insulating plastics material (not shown), which circuitry can conveniently comprise an electronic circuit implemented as a large scale integrated circuit having an electronic multiplier, a voltage-to-frequency converter and a counter (also not shown). The multiplier would have a first pair of inputs connected to receive a signal representative of the current I flowing in the live wire, this current-representative signal being produced by a shunt series connected in the live wire, and would have a second pair of inputs connected to receive a signal representative of the voltage V between the live

and neutral wires, this voltage-representative signal conveniently being produced by a potential divider. An output signal produced by the multiplier would therefore be representative of the instantaneous value of the product IV ₁ which when applied to the converter would provide output pulses having an instantaneous pulse rate dependent on the product IV. This signal would then be summed and integrated with respect to time to provide an indication of the energy consumed.

Figure 3 shows a first embodiment of the invention, wherein there is provided an electricity meter having meter installation, 10, for a single phase domestic application, where an electrical source, 12, is provided with live and neutral terminals, 14, 16, which lead directly to a meter 18 at each premises supplied with electricity. Such a meter, 18, is placed between the electricity supply and cabling within the premises for electrical fittings, and has input terminals for livei _n and neutral^ respectively, 20 & 22, and output terminals for live _out and neutraLt respectively, 24 & 26. The current is measured passing through the live conductor and the voltage is measured across the load, 28, which is connected between the livei _n and neutral^ terminals. A safety earth cable, 30, runs in parallel with the live and neutral cables. Typically the earth cable is connected to the neutral potential. In contrast with the arrangement shown in Figures 1 & 2, current detector, 32, and voltage detector, 34, are each connected to circuitry, 36. Circuitry 36, in addition to taking a supply, ordinarily, from the metered electricity supply, is provided with a back-up power supply, 38. Back-up power supply, 38, can comprise electrical cells such as lithium-ion cells to provide a long-life capability to supply electrical energy or may comprise rechargeable cells which are continuously trickle-charged in ordinary usage of the meter. By the use of a comparator (not shown) between the current sensor, 32, and the voltage sensor, 34, an event can be determined when current flow occurs through the current senor, 32, but voltage sensor, 34, determines no potential difference between the output terminals and this circuitry can be employed to indicate when fraudulent attempts have been attempted. Other methods of determining the occurrence of a fraud are also possible.

Thus, when an attempt to obtain an un-metered supply of electricity is made, which employs the by-passing of electrical terminals by disconnection and the current measuring circuit remains in operation, the current, when multiplied by a default value for

voltage across a load, can enable a good estimate of the amount of un-metered electricity to be determined, which may be reclaimed by virtue of an appropriate factor, to reflect the extra costs involved in effecting a repair. Fraudulent use of such arrangements can take place when one or other of the neutral terminals, 22, 26 are disconnected and, as discussed above, in the case of a typical alternating current meter, un-metered electricity can, in principle, be obtained by removal of the neutral connection from the meter so that it is no longer capable of measuring voltage as applied across a load.

Thus, in operation, if the consumer attempts to steal electricity, by disconnection of terminals not employed in current measurement, the lack of potential difference between output terminals of the meter will indicate fraud and a default value of voltage multiplier will be employed to determine a suitable levy instead of exact measured supply of energy. The circuit can be operated so that it is constantly measuring the current in the current measurement circuit, or it could be operated so that it makes periodic or random measurements of the current.

The meter may also be provided with a circuit breaker whereupon the occurrence of fraud, then the circuit breaker may operate after a predetermined time interval, amount of electricity has been consumed or otherwise. Alternatively a current limiter (not shown) could be provided which limits the amount of current that can flow through the meter once fraud has been established. However, when the net current flowing through the current limiter exceeds a given threshold level, the current limiter could operate a circuit breaker. The circuit breaker/limiter (not shown) could operate to disconnect/limit the consumer's supply of power, since although the contacts in the neutral wire will have been by-passed, the live wire would not have been so by-passed.

By appropriate selection of the operating characteristics of the multiplier, the converter and the counter, the compensation can be made relatively accurate, or indeed substantially increased to overcompensate and thus penalise the consumer for attempting to steal electricity.

The circuitry associated with the meter could be fitted with a flashing LED light which shows that a meter has been tampered with. The LED or other visible warning

means could also be arranged to flash a continuous warning light, to discourage the consumer from continuing attempting to steal electricity.

Additionally if the meter is operable to measure the current flowing through the neutral connection, it would be similarly able to measure the consumed power should the live connection to the meter be removed. Finally, although the various aspects of the invention have been described in relation to electronic electricity meters, they are also applicable, with appropriate modifications, to electromechanical electricity meters.