GB2260415A

GB2260415A - Power meters

Info

Publication number: GB2260415A
Application number: GB9219273A
Authority: GB
Inventors: Kenneth Payne; Roger Henry King; David Alexander Watson
Original assignee: Ampy Automotion Digilog Ltd
Current assignee: Landis and Gyr Ltd
Priority date: 1991-10-12
Filing date: 1992-09-11
Publication date: 1993-04-14
Anticipated expiration: 2012-09-11
Also published as: GB2260415B; GB9121718D0; GB9219273D0

Abstract

A power meter includes voyage measuring means (10, 3, 14, 17, 5) for generating a fault condition signal if the voltage between the LIVE and NEUTRAL lines (1, 2) supplying the meter departs from a predetermined value, e.g. due to tampering. Departures are recorded and disconnection of the supply to a load may be effected (9, 4) if the number of departures exceeds a predetermined value. Overvoltage events are also recorded. Non-volatile memory means is provided to store the total energy consumed by a load. <IMAGE>

Description

Title: Improvements in and relating to electricity supplies Field of the Invention This invention concerns electricity supplies and the detection of supply failures, overvoltage conditions and fraudulent usage of electricity involving non payment therefor.

Background to the Invention It has been known for some time that electricity consumption meters can be defrauded by tapering with the incoming and outgoing connections. One particular method relies on the removal of both Neutral wires from the meter. The Neutral is bonded to the protective earth in most installations and when the Neutral is disconnected, the load return current is caused to flow via the protective earth. The result of this is that mains supply potentials are still available to the load, but the voltage measuring element of the meter is presented with zero potential. If the potential is measured as zero the resulting calculated value of consumed power is also zero, and the consumer obtains electricity without the units being recorded.

In a meter comprising only a measuring element, (mechanical or static) and a register, it is not possible to detect such conditions unless the installation is inspected at a time for example when the Neutral leads have been fraudulently disconnected.

With the introduction of so-called intelligent metering these conditions can be detected and acted on, and the particular fraud described above can also be overcome.

Hitherto it has been proposed to measure the currents flowing in both Live and Neutral wires and if a marked difference is detected, merely fla an error or fault condition.

Summary of the Invention According to the present invention in a power measuring meter adapted to measure electrical power supplied from a supply to a load, circuit means is provided for generating an unregulated voltage proportional to the supply voltage, further circuit means is provided for monitoring the unregulated voltage, and threshold detector means is combined therewith for generating a fault condition signal if the monitored voltage falls below a predetermined threshold value.

The monitoring may be intermittent (either at regular intervals or randomly) or continuous.

Should a fault condition signal be generated, control circuit means within the meter can be adapted to respond accordingly and may for example disconnect the supply from the load.

By counting the number of fault condition signals generated and maintaining a running total which can be subseauently checked, any discrepancy between known supply failures and the running total can be spotted.

In one embodiment of the invention the further circuit means is adapted to continuously measure the unrelated voltage generated from the incoming mains supply, and if this voltage falls below a predetermined value control means is adapted to undertake various tasks such as:- to save important data in a non-volatile memory device to enable the meter to become fully functional without the loss of information when power is restored; to increment a register, which totalizes the number of power failures detected and to store this total in non-volatile memory; and to open switch means to thereby disconnect the meter from the electricity supply, so that the consumer can no longer obtain power from the supply.

In order to permit an orderly shutdown as aforesaid and enable one or more of the above tasks to be performed, storage circuit means may be provided within the meter for storing electrical energy derived from the suply during normal operation of the meter to provide a supply of electrical energy to power at least the fault condition signal generating means for a short period of time after the monitored voltage drops below the threshold value.

The invention also lies in a method of detecting a power supply failure in the LIVE and NEUTRAL of a supply to a power measuring meter comprising the steps of continuously monitoring the supply voltage and generating a fault condition signal if the measured value falls below the predetermined threshold value.

Without other information the meter cannot of course determine whether the fault condition signal is due to a genuine power failure or a temporary voltage reduction or whether it is due to tampering with the supply connections to the meter. To this end pulse counter means may be provided to count the number of fault condition signals generated and storage means, preferably in the form of non-volatile memory may be provided in which the accummulating number of fault condition signal occurrances can be stored.

Preferably the counter means is updated before its value is stored in the non volatile storage means. The stored number can be inspected at intervals by an electricity company employee and the value can be compared with a value known by the electricity company of genuine power failures, to indicate whether tampering with the meter has occurred. Thus for example, if a consumer disconnects the Neutral supply line from a meter constructed in accordance with the present invention, the event is recorded and the installation may be automatically disconnected from the supply. The disconnection will deter future attempts at fraud.

If the power failure is innocent, then the fact that the contactor is open will prevent any incorrect supply potentials reaching the customer's load until the fault is rectified and the supply is restored.

It is a feature of the invention that if an excess voltage occurs, this condition can also be detected using a threshold circuit and a different fault condition signal may be generated. Some or all of the tasks as set out above may be initiated, and a further counter may be incremented by one, to indicate that an over voltage condition has been detected. For safety purposes an over voltage condition may be arranged to disconnet the meter from the supply to prevent damage to the load from excessive voltage being applied thereto.

In order to preserve the running total of units of electricity consumed by the load, the running total may be stored in a non-volatile memory or may be transferred to a non-volatile memory in the event of the operation of a fault condition signal as aforesaid.

Description of the illustrated embodiment The invention will now be described with reference to the accompanying drawing in which the single Figure is a circuit diagram of apparatus embodying a detection circuit primarily aimed at detecting and recording fraudulent use of electricity, in accordance with the invention.

Referring to the drawing, the incoming mains supply is connected to the meter at points 1 and 2. The Neutral wire 2 is connected straight through the meter and the Neutral load connection is made at 8. The Live connection passes via the measuring element 11 to a main contactor 4 and auxilliary contactor 7. The load is connected at Point 12.

The low voltage supply for the controller 5 is derived from the mains supply by transformer 10 rectifier 3 and reservoir capacitor 14. The potential across capacitor 14 is an unregulated voltage which is proportional to the supply voltage. This unregulated voltage is maintained below a particular value by a voltage regulator 13 to provide power for the controller 5.

The capacitor 14 forms a local power storage device for the contactor 4 and auxiliary contactor 7, via circuit elements 15, 16. This maintians the supply to contactors 4 and 7 during short duration power failures.

A sample of the unregulated supply is provided by a potential divider 17 which produces a siganl representative of the unregulated voltage 17. The potential at point 17 is converted to digital data by an analog to digital converter within the controller 5. The digital value thereby obtained is continuously compared in the controller 5. If the value falls below a qiven value, the controller 5 initiates an orderly power down sequence, the final action of which is to open the main contactor 4 by means of a signal along line 9 and to open the auxiliary contactor by means of a signal along line 6.

The values of the circuit elements 10, 3 and 14 producing the unregulated voltage are chosen such that there will be sufficient energy in the reservoir capacitor 14 to allow the controller to perform its shut down functions correctly, before a collapsing supply voltage causes the regulated voltage supplied to the controller to collapse completely.

The main contactor is bistable in operation, ie there is an ON control input and an OFF control input, and the contactor remains latched in either the ON or OFF state even when all power is removed. This reduces the power requirements of the meter.

The values of the circuit elements 15 and 16 providing the local power for the contactors are chosen such that there is enough energy stored in capacitor 15 after power failure for the contactors to be operated correctly by pulse signals along lines 6 and 9.

The controller 5 is not only programmed to initiate an orderly shutdown but also to generate a fault condition signal on each said occurrance which fault signals can be accummulated to give an indication of the number of times the supply to the meter has 1,failed".

The controller 5 may also be programmed to initiate an orderly shutdown and generate a different fault condition signal if the potential at 17 and therefor the digital value derived therefrom exceeds a threshold value. The "different" fault condition signals may be accumulated to indicate the number of overvoltage conditions seen by the meter.

Although not shown a register containing the running total of units of electricity measured by the meter may be provided and either it is a so-called non-volatile device or the numerical value in the register is transferred to a non-volatile memory in the event that a fault condition signal is generated.

Claims

1. A power measuring meter adapted to measure electrical power supplied from a supply to a load circuit wherein means is provided for generating an unregulated voltage proportional to the supply voltage, further circuit means is provided for monitoring the unregulated voltage, and threshold detector means is combined therewith for generating a fault condition signal if the monitored voltage supply voltage falls below a predetermined threshold value.

2. A power measuring meter as claimed in claim 1, wherein the monitoring is intermittent.

3. A power measuring meter as claimed in claim 2, wherein the monitoring is performed at regular intervals.

4. A power measuring meter as claimed in claim 2, wherein the monitoring is performed at randomly occurring points in time.

5. A power measuring meter as claimed in claim 1, wherein the monitoring is continuous.

6. A power measuring meter as claimed in any of claims 1 to 5, further comprising control circuit means adapted to respond to the generation of a fault condition signal to at least disconnect the supply from the load.

7. A power measuring meter as claimed in any of claims 1 to 6, further comprising non-volatile memory means for storing data generated by the meter.

8. A power measuring meter as claimed in claim 7, further comprising control means for entering selected items of the said data within the said memory means if the monitored voltage falls below a predetermined value, thereby to enable the meter to become fully functional without loss of information when power is restored.

9. A power measuring meter as claimed in claim 7 or 8, further comprising register means and register control means for incrementing the register means for each power failure defined by a drop in the monitored voltage below the threshold value, thereby to record as a running total within the register a numerical value which is proportional to the number of power failures detected.

10. A power measuring meter as claimed in claims 8 and 9, wherein the control means enters the value of the register running total into the said memory means as a selected item of data if the monitored voltage falls below the predetermined value, the control means operating so as to permit the register total to be incremented by the newly detected power failure before entering the register value in the said memory means.

11. A power measuring meter as claimed in claim 10, further comprising switch means for disconnecting the meter from the electricity supply so that the load will not thereafter receive energy from the supply via the meter if the numerical value in the register means exceeds a predetermined value.

12. A power measuring meter as claimed in any of the preceding claims further comprising storage circuit means for storing electrical energy derived from the supply during normal operation of the meter to provide a supply of electrical energy to power at least the fault condition signal generating means for a short period of time after the value of the monitored voltage drops below the threshold value.

13. A power measuring meter as claimed in any of claims 1 to 12, in which the threshold detector means also generates a second fault condition signal if the monitored voltage exceeds a second threshold value.

14. A power measuring meter as claimed in claim 13, wherein the second fault condition signal is a different fault condition signal from that generated by a drop in the monitored voltage.

15. A power measuring meter as claimed in claim 14, further comprising second register means which is incremented in response to the generation of each fault condition signal.

16. A method of detecting a power supply failure to a power measuring meter comprising the steps of monitoring the voltage between the LIVE and NEUTRAL supply lines feeding the meter and generating a fault condition signal if the monitored voltage value falls below a predetermined threshold value.

17. A method as claimed in claim 16, further comprising the step of incrementing a running total in an accumulator for each fault condition signal generated by the meter.

18. A method as claimed in claim 17, further comprising the step of entering the updated running total in a nonvolatile memory as each fault condition occurs.

19. A method as claimed in claim 18, wherein the running total value stored in the volatile memory is re-entered in the register when the power is restored.

20. A method as claimed in any of claims 16 to 19, further comprising the step of accumulating electrical energy in storage circuit means whilst the meter is operating normally so as to provide a source of electrical energy for generating at least the fault condition signal following a drop in the monitored voltage below the threshold value.

21. A method of detecting overvoltage in a power supply connected to a load through a power measuring meter comprising the steps of monitoring the voltage between the LIVE and NEUTRAL supply lines feeding the meter and generating an overvoltage fault condition signal if the monitored voltage value exceeds a predetermined threshold value.

22. A method as claimed in claim 21, further comprising the step of disconnecting the meter from the supply voltage if an overvoltage fault condition signal is detected.

23. A method as claimed in any of claims 16 to 22, wherein data relating to the quantity of electrical energy consumed by the load connected to the meter is stored in non-volatile memory means whenever a fault condition signal is generated.

24. A power measuring meter constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.