Title of Invention

AN ELECTRONIC ENERGY METER OPERATING ON A.C. SUPPLY DETECTING PILFERAGE OF ELECTRIC ENERGY AND EARTH LEAKAGE CURRENT

Abstract Abstract An electronic energy meter operating on A.C. supply with provision for detecting pilferage of electric energy and earth leakage current characterised by a first current transformer with high accuracy measurement capacity and a second current transformer with a lower accuracy measurement capacity, both current transformers would with a single-turn primary for carrying the forward and return current paths such that the magnetising flux generated by the load current is additive in the first current transformer, but subtractive in the second current transformer; an electronic circuit, provided for the output of the second current transformer, said electronic circuit incorporating a bias generator connected to a rectifier-cum-low pass filter and a driver circuit; a microprocessor or microcontroller connected to the said electronic circuit.
Full Text This invention relates to an electronic energy meter with provision for detecting pilferage of electric energy and earth leakage current.
This invention also relates to a static electronic meter for accurate measurement of electric energy delivered from the commercial AC mains supply.
The conventional induction type energy meters (also known as kilowatt -hour meters) are mechanically complex and employ several gear wheels for measuring the rpm of a non - magnetic vane rotating at a speed proportional to the instantaneous load power consumed. The assembly requires several precision mechanical components and is highly labour intensive for testing and calibration. The meter has the disadvantage of accuracy drifts, susceptibility to tampering and fragility. It is also incompatible with the energy management systems being widely adopted in recent times.
This invention relates to an electronic energy meter (EEM) for accurate measurement of commercial mains power and monitoring of tampering, if any, by the electricity consumer. An Application Specific Integrated Circuit (ASIC) has been designed for the high-volume, low-cost EEM proposed herein.
The said EEM incorporates an integrated microprocessor and control programme which performs the ftinctions of energy measurement, with

intelligent detection of tampering and resultant energy pilferage. The lower component count of an ASIC based EEM would reduce the power consumption, material and production costs besides being much more reliable than conventional rotating vane energy meters or those based on discrete electronics technology using standard ICs.
The electronic measurement of energy for an AC waveform involves accurate multiplication of the voltage and current on a cycle - to -cycle basis and integrating this value for calibration as energy consumption by the load.
The invention proposed herein effectively utilizes the intelligence and programmability of the microprocessor embedded in the ASIC for the detection of energy pilferage and at the same time enables the EEM to continue accurate metering at the consumer end.
Virions other features of this invention will be apparent from the further description thereof given hereunder.
The electronic energy meter, according to this invention, operating on A.C. supply, characterised by a first current transformer with high accuracy m easurement capacity and a second current transform er with a lower accuracy measurement capacity, both current transformers wound with a single-turn primsu^y for carrying the forward and return current paths such that the magnetising flux generated by the load current is additive in the first current transformer, but sub tractive in

the second cmrrent transformer; an electronic circuit, provided for the output of the second current transformer, said electronic circuit incorporating bias generator connected to a rectifier-cum-low pass filter and a driver circuit; a microprocessor or microcontroller connected to the said electronic circuit.
This invention will now be described in further detail with reference to the accompanying drawings wherein
Fig.l illustrates the normal conventional meter connections
Fig,2 illustrates a line load interchange in the connections
FigJA and 3B illustrate earthed load and input/output interchange and earthed load
Figs. 4A and 4B illustrate line neutral reversal and earthed load and input/output interchange and line neutral reversal and earthed load
Fig. 5 illustrates the first and second current transform er connections of one of possible embodiments of the EEM proposed herein.
Fig.6 illustrates the electronic circuit of the said embodiment provided at the

secondary of the second current transformer
and Fig. 7 illustrates the system configuration of the said embodiment
The problem of energy pilferage by tampering with the energy meter is quite common in our country and abroad. It is estimated that about 20 - 30 % of the electrical energy distributed by the utilities is lost by pilferage.
The most common methods of energy pilferage are:
a) .bypassing the current circuit of the meter fully or partially.
b) .changing the polarity of either voltage or current sensing circuit resulting
in a negative power / energy registered. An easy way is to reverse the line and load connections.
c) .interchanging the phase and neutral connection and using an earthed load.
Fig. I gives the power circuit coimections of the conventional energy meter connected in a typical house wiring configuration. The phase and lieutral connections are applied to the load throu^ an accurate current transformer in the phase line measuring the current drawn.
This method suffers fi-om the following disadvantages:

a) .if the line and load are interchanged with each other, the current measured by the CT is of opposite polarity to the line voltage, resulting in negative power and energy indicated (Fig. 2)
b) .if the load circuit or part of it is earthed under a) above, then a portion of the current is drawn through local earth (Figs. 3A and 3B) and goes unmetered.
c) .if the line and neutral are interchanged and load current drawn through local earth, no return current will flow through CT and hence goes unĀ¬metered (Figs.4A and 4B)
The EEM proposed herein indicates any of the above energy pilferage methods on an LED, thus effectively foiling this activity. Two CTs (Fig.5)are used, one main with high accuracy (measurement class), and another lower performance Tamper Detection CT (TDCT) which can be about two or three times less accurate.
Both CTs are wound with a single - turn primary carrying the forward and return current paths, so that the magnetising flux generated by the load current is additive for the main CT, but subtractive m the TDCT.
The result of this connection is that during normal conditions of loading, the

main CT will carry twice the ampere turns, which will be the data used for accurate energy measurement and monitoring. However, the TDCT will generate zero ampere turns, resulting in a zero output at its secondary.
When tampering takes place by method (a) above, the status quo is maintained and accurate energy measurement continues. When a part of the load is connected to earth instead of the neutral line, (i.e. pilferage method b & c above), the cmrent return path of this load circuit is through the local earth, which will result in a lower reading from the main CT than would have been otherwise expected. However, the TDCT output suddenly shoots up, its output being dependent upon the amount of current imbalance, (that is,, the current pilfered). This voltage output depends upon the value of the burden resistance . Though the accuracy of measurement will be lower than the main CT, the TDCT can be set to measure energy employing a punitive factor to discourage fiirther pilferage by tampering with the meter cormections.
The electronic circuit of Fig. 6 is a cost - effective means of indicating such a tampering on an LED in the meter front panel. It consists of a bias generator Rl- Dl, rectiJBer - cum -low pass filter R2, R3, D2, CI and driver circuit R4, R5, D3. The output of this circuit is read by the input port of a microprocessor or microcontroller, and a new energy measurement algorithm is initiated by software using the outputs from the main CT and TDCT together.

In short, the EEM proposed herein employs one low - cost CT in addition to the main measurement CT. These CTs have their primary windings carrying both the forward and return current path with additive - subtractive flux coupling. Zero output on the TDCT indicates tamperfree operation. Any output on the TDCT shows that the meter connections have been tampered with. The additional cost of the said EEM (as compared to the conventional energy meter) is marginal since only a low - cost CT and a few electronic components are required extra. At the same time, measurement accuracy is maintained.
The sensitivity of the circuit can be varied by changing the value of R2. Thus, even very small differences in the forward and return currents can be interpreted. This makes the circuit usable as an effective earth leakage detector since differences of the order of a few milliamps are usually attributable to earth leakage in the building wiring. In this mode, the said EEM can be used for earth leakage detection and protection also.
The terms and expressions in this specification are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the EEM proposed herein are possible without departittg from the scope and ambit of this invention.


We Claim:
1. An electronic energy meter operating on A.C. supply with
provision for detecting pilferage of electric energy and earth leakage current characterised by a first current transformer with high accuracy measurement capacity and a second current transformer with a lower accuracy measurement capacity, both current transformers wound with a single-turn primary for carrying the forward and return current paths such that the magnetising flux generated by the load current is additive in the first current transformer, but subtractive in the second current transformer; an electronic circnit, provided for the output of the second current transformer, said electronic circuit incorporating a bias generator connected to a rectifier-cuni-low pass filter and a driver circuit; a microprocessor or microcontroller connected to the said electronic circuit.
2. An electronic energy meter operating on A.C.
supply with provision for detecting pilferage of

electric energy and earth leakage current substantially as herein described with reference to and as illustrated in Figs. 5 to 7 of the accompanying drawings.

Documents:

2339-mas-1996 abstract duplicate.pdf

2339-mas-1996 abstract.pdf

2339-mas-1996 claims duplicate.pdf

2339-mas-1996 claims.pdf

2339-mas-1996 correspondence others.pdf

2339-mas-1996 correspondence po.pdf

2339-mas-1996 description (complete) duplicate.pdf

2339-mas-1996 description (complete).pdf

2339-mas-1996 drawings duplicate.pdf

2339-mas-1996 form-1.pdf

2339-mas-1996 form-26.pdf


Patent Number 198044
Indian Patent Application Number 2339/MAS/1996
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 23-Dec-1996
Name of Patentee ELECTRONIC RESEARCH & DEVELOPMENT CENTRE,
Applicant Address VELLAYAMBALAM, THIRUVANANTHAPURAM 695033, UNIT OF ER & DCI
Inventors:
# Inventor's Name Inventor's Address
1 SANJEEVA RAO KRISHNAKUMAR RAO HARDWARE DESIGN CENTRE, ELECTRONIC RESEARCH & DEVELOPMENT CENTRE, VELLAYAMBALAM, THIRUVANANTHAPURAM 695033, UNIT OF ER & DCI
2 RAVI VARMA THAMPI RAVINDRA KUMAR HARDWARE DESIGN CENTRE, ELECTRONIC RESEARCH & DEVELOPMENT CENTRE, VELLAYAMBALAM, THIRUVANANTHAPURAM 695033, UNIT OF ER & DCI
3 BIJU CHERIAN OOMEN HARDWARE DESIGN CENTRE, ELECTRONIC RESEARCH & DEVELOPMENT CENTRE, VELLAYAMBALAM, THIRUVANANTHAPURAM 695033, UNIT OF ER & DCI
PCT International Classification Number G01R21/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA