AN ELECTRICITY METER CAPABLE DETECTING THE MEASUREMENT
UNCERTAINTY

FIELD OF THE INVENTION

[001] The present invention generally relates to an electricity meter capable of detecting the measurement uncertainty, and more particularly, but not exclusively, to the electricity meter detects a voltage drift, a current drift and a phase angle drift occurred in the each phase lines with respect to the neutral line.

BACKGROUND OF THE INVENTION

[002] Today electricity has become a necessity rather than a mere need, and it is equally important to accurately measure the consumption of the same. Measurement accuracy is the top most requirements for any power & energy monitoring devices, irrespective of it is being used for revenue/billing application or for energy management. Employing the latest technology it is possible to produce high accuracy devices. But the challenge lies in the fact that this accuracy should be maintained throughout the lifetime of the product.

[003] As we all are aware that accuracy of measurement drifts over the time, this could be due to normal ageing of the components, parts etc or due to the influences of external environment in which they are operating. There is no proven method so far to characterize this behavior, since there are many complex environmental factors involved. Neither there is any non invasive method to quantify it except comparing periodically with external references on site or sending back to nearby service centers, which is not very convenient since it has to be done off line, means interruption of service and also involves lot of efforts. Hence cannot be recommended more frequently.

[004] Therefore, a non invasive method of identifying the drift, trends etc and characterizing them by capturing and applying the real life scenario, environments etc not only help the users in planning the recalibration accurately for the normal ageing related drift and also help them in identifying any abrupt changes in the accuracy of the measurement due to any random events or any sudden component degradations.

[005] Accordingly there is a need in the art to provide a solution to one or more of above said problems. The present invention solves one or more of these problems in a unique and economical manner.

SUMMARY OF THE INVENTION

[006] It is a feature of the present invention is to provide a system which substantially overcomes the one or more of the above mentioned disadvantages.

[007] It is the principal object of the present embodiment is to provide an electricity meter which is capable of identifying the measurement uncertainty.

[008] Another object of the present embodiment is to provide the electricity meter which detects a measurement uncertainty such as a voltage drift, a current drift and a phase angle drift occurred in the each phase lines with respect to the neutral line.

[009] In one aspect of the present embodiment an electricity meter which is capable of detecting a measurement uncertainty without disturbing a normal operation is provided. The electricity meter includes (a) one or more phase lines and a neutral line, (b) one or more current measuring means which are positioned in a current measuring path, (c) a voltage measuring means which is positioned in a voltage measuring path, (d) one or more controlling switches which are positioned prior to each of the current measuring means and the voltage measuring means, and (e) a microcontroller which is configured (i) to selectively control at least one of the one or more controlling switches at a predefined interval and (ii) to detect the measurement uncertainty in the electricity meter. The one or more phase lines include a first phase line, a second phase line, and a third phase line. In the current measuring path, the first phase line, the second phase line and the third phase line are positioned in parallel to each other and the first phase line, the second phase line and the third phase line are connected in series with the neutral line. In the voltage measuring path, the first phase line, the second phase line, the third phase line and the neutral line are positioned in parallel to each other. The microcontroller selectively controls at least one of the one or more controlling switches (i) to measure a current passed through each of the first phase line, the second phase line, the third phase line and the neutral line by the current measuring means (ii) to measure a voltage passed through each of the first phase line, the second phase line, the third phase line and the neutral line by the voltage measuring means individually. The microcontroller receive and compare (a) the current and the voltage measured in the first phase line, the second phase line and the third phase line with (b) the current and the voltage measured in the neutral line individually. The microcontroller provides an alert when a difference between the current and the voltage measured in at least one of the one or more phase lines and the neutral line is exceeds a threshold. The electricity meter also includes one or more phase detecting means which are positioned between each of the plurality phase, lines of the current measuring path and the voltage measuring path. The one or more phase detecting means detects a phase angle drift and communicates to the microcontroller. The alert includes a visual indication, an internal log or an audio indication. The uncertainty includes a current drift, a voltage drift and a phase angle drift.

BRIEF DISCRIPTION OF THE ACCOMPANYING DRAWINGS

[0010] The advantages and features of the invention will become more clearly apparent from the following description which refers to the accompanying drawings given as non-restrictive examples only and in which:

[0011] Figure 1 illustrates an electricity meter capable of identifying a measurement uncertainty in accordance to a preferred embodiment herein;

[0012] Figure 2 illustrates a current measuring unit of the electricity meter shown in figure 1 in accordance to a preferred embodiment herein; and

[0013] Figure 3 illustrates a voltage measuring unit of the electricity meter shown in figure 1 in accordance to a preferred embodiment herein.

DETAILED DISCRIPTION OF THE INVENTION

[0014] The present invention will be described herein below with reference to the accompanying drawings. An electricity meter capable of online detection and self tracking of measurement uncertainty is described.

[0015] The following description is of exemplary embodiment of the invention only, and is not limit the scope, applicability or configuration of the invention. Rather, the following description is intended to provide a convenient illustration for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the structural/operational features described in these embodiments without departing from the scope of the invention as set forth herein. It should be appreciated that the description herein may be adapted to be employed with alternatively configured devices having different shaped, components, and the like and still fall within the scope of the present invention. Thus the detailed description herein is presented for purposes of illustration only and not of limitation.

[0016] The present embodiments provides an electricity meter capable of online detection and self tracking of measurement uncertainty, and more particularly, but not exclusively, to the electricity meter detects a voltage drift and a current drift occurred in the each phase line with respect to the neutral line. For illustrative purpose the three phase electricity meter is taken as example and the proposed system and method is implemented therein. However, the electricity meter with n-phases may be implemented using the proposed system and method.

[0017] Figure 1 illustrates an electricity meter 100 capable of identifying a measurement uncertainty in accordance to a preferred embodiment herein. The electricity meter 100 is a three phase electricity meter and hence it includes three phase lines R, Y, B and a neutral line N. The three phase lines R, Y, B and the neutral line N are connected to a microcontroller 106 through a current measuring unit (e.g. current measuring path) 102 and a voltage measuring unit (e.g. voltage measuring path) 104. The microcontroller 106 is configured to (i) receive the voltage and current measurement from the voltage measuring unit 104 and the current measuring unit 102, (ii) perform normal operation i.e. measuring the power consumption and (iii) identify the measurement uncertainty. The measurement uncertainty includes a voltage drift, a current drift and a phase angle drift. The microcontroller 106 and the voltage measuring unit 104 are configured to detect the voltage drift in each phase line of three phase lines R, Y, B. Similarly, the microcontroller 106 and the current measuring unit 102 are configured to detect the current drift in each phase line of three phase lines R, Y, B. The electricity meter 100 also include phase detecting means P1-P3 which are connected between each phase lines R, Y, B of the current measuring unit 102 and the voltage measuring unit 104. The phase detecting means P1-P3 detects the phase angle drift between the phase lines and communicates to the microcontroller 106. The phase detecting means P1-P3 could be a phase angle measurement IC or the microcontroller 106 can internally derive it from respective voltage and current lines being diagnosed, i.e. cos _1(W1 / VA1). Wl is the active power in watt and VA1 is the apparent power for phase line R

[0018] The electricity meter 100 also includes an indication means 108, a display 110, and a communication means 112. The display 110 displays the measured power consumption received from the microcontroller 106. The indication means 108 is used to indicate the measurement uncertainty identified in the microcontroller 106. In one embodiment, the indication means 108 includes a memory device which stores the logs of measurement uncertainty detected in the microcontroller 106. For example, the log includes (a) a time at which the measurement uncertainty detected, (b) the type of measurement uncertainty detected such as the voltage drift, current drift and the phase angle drift and (c) phase line at which the measurement uncertainty is detected. In another embodiment, the indication means 108 is a visual indication which includes a light source to indicate the measurement uncertainty. In yet another embodiment, the indication means 108 is an audible indication which includes a buzzer to indicate the measurement uncertainty.

[0019] Figure 2 illustrates the current measuring unit 102 as shown in figure 1 in accordance to the preferred embodiment herein. The three phase lines R, Y, B and the neutral line N are connected to the microcontroller 106 through the current measuring unit 102. The current measuring unit 102 includes three controlling switches SW1-SW3 which are positioned in each of the three phase lines R, Y, B. The current measuring unit 102 also includes four measuring means CT1-CT4 (current measuring means) which are positioned in each of the phase lines R, Y, B and the neutral line N. Among the measuring means CT1-CT4, the measuring means CT4 should include the characteristics of a high integrity and a tighter tolerance. The measuring means CT1-CT4 are depicted as a current transformer but it can be replaced by any device which is suitable for measuring the current. The current measuring means CT1-CT4 are positioned prior to the controlling switches SW1-SW3. The controlling switches SW1-SW3 are depicted as relay and it can be replaced by any switching device which is operating similar to the switching device SW1-SW3. In the current measuring unit 102 the phase lines R, Y, B are positioned in parallel and connected in series with the neutral line N as shown in the figure 2. The each of the phase lines R, Y, B are include sub phase lines Rl, R2, Yl, Y2, Bl and B2. The controlling switches SW1-SW3 are positioned in each of the sub phase lines Rl, Yl and Bl respectively. The controlling switches is controlled to transfer the current received in the sub phase lines Rl, Yl and Bl to the sub phase line R2, Y2 and B2 via the measuring means CT4 or directly to the sub phase lines R2, Y2 and B2 respectively.

[0020] During the normal mode of operation, the controlling switches SW1-SW3 are maintained in the normally open (NO) position and thus allows the current received from the sub phase lines Rl, Yl and Bl are measured using the measuring means CT1-CT3 respectively. The measuring means CT4 measure the neutral current. During diagnostic mode, the microcontroller selectively changes the position of controlling switches from NO position to NC position to identify the measurement uncertainty i.e. the current drift. To measure the current drift in phase line R, the microcontroller controls the position of the controlling switches SW2 and SW3 from NO position to NC position and retains the other switches SW1 in the NO position. In this scenario, the current received in the sub phase line Rl is passed through the measuring means CT1 and the CT4. The current received from other phase lines Yl and Bl directly bypassed to the sub phase lines Y2 and B2. The microcontroller receives the measured current value from the CT1 and the CT4 and computes the variance of phase line R using the formula.

variance = ((Iphase - In) / In) * 100

Wherein,

In = measured current received from the neutral line Iphase = measured current received from the phase line.

[0021] To identify the current drift in the phase line Y, the microcontroller controls the position of the controlling switches SW1 and SW3 from NO position to NC position and retains the other controlling switches SW2 in the NO position. In this scenario, the current received in the sub phase line Yl is passed through the measuring means CT2 and the CT4. The microcontroller receives the measured current value from the CT2 and the CT4 and computes the variance of phase line Y. To identify the current drift in the phase line B, the microcontroller 106 controls the position of the controlling switches SW1 and SW2 from NO position to NC position and retains the other controlling switches SW3 in the NO position. In this scenario, the current received in the sub phase line Bl is passed through the measuring means CT3 and the CT4. The microcontroller 106 receives the measured current value from the CT3 and the CT4 and computes the variance of phase line B. The microcontroller 106 compares the variance computed for each of the phase lines with the threshold value. The threshold value is in the range of 0.1-1.0 which is defined by the manufacturer of the electricity meter during the production. The microcontroller 106 sends notification to indication means 108 when the variance of the at least one phase line R, Y, B exceeds the threshold value. The notification includes at which phase line the variance exceeds the threshold value. For example, when the variance of the phase line B exceeds the threshold value then the notification includes the current drift detected in the phase line B. In one scenario, the variance detected in the all phase lines R, Y, B are same then the drifting is occurred in the neutral line N. The microcontroller 106 notifies the indication means 108 about the neutral line drift in this scenario. The microcontroller 106 controls the mode of operation (i.e. switching from normal mode to diagnostic mode and vice versa) of the electricity meter 100 based on the predefined time interval which is specified in the microcontroller 106.

[0022] Figure 3 illustrates the voltage measuring unit 104 as shown in figure 1 in accordance to the preferred embodiment herein. The three phase lines R, Y, B and the neutral line N are connected to the microcontroller 106 through the voltage measuring unit 104. The voltage measuring unit 104 includes four controlling switches T1-T4 which are positioned in each of the three phase lines R, Y, B and the neutral line N. The voltage measuring unit 104 also includes an Analog to Digital converter (ADC) (voltage measuring means - not shown in figure) which is connected to the three phase lines R, Y, B and the neutral line N through the voltage limiting circuits Z1-Z4. As shown in the figure 2 the each of the phase lines R, Y, B are connected in series with a neutral line N. The controlling switches T1-T4 are depicted as transistor and it can be replaced by any device which is operating similar to the transistor Tl-T4. The controlling switches T1-T4 receive input from the phase lines R, Y, B and the neutral line N as well as receive the input from the microcontroller 106.

[0023] During the normal mode of operation, the controlling switches Tl is turned into saturation mode and the other controlling switches T2-T4 are turned off and thus allows the voltage received from the phase lines R, Y, B are transferred to the ADC through voltage limiting circuits Z2-Z4 respectively. During a diagnostic mode, the microcontroller selectively turns off the Tl and turns on one of the controlling switches T2-T4 (one at a time) from off mode to the saturation mode vice versa to identify the measurement uncertainty i.e. the voltage drift. To measure the voltage drift in phase line R, the microcontroller 106 turns the transistor T2 to a saturation mode and the other transistors Tl, T3 and T4 remain turned off. In this scenario, the same voltage is passed through the phase line R and the neutral line N i.e. the same voltage is passed to the ADC through the current limiting circuits Zl and Z2 from the phase line R and the neutral line N. The microcontroller 106 computes the variance for the phase line R using the ADC readings received from the phase line R and the neutral line N. The variance is calculated using the below formula

Variance = ((Vphase - Vn) / Vn) * 100

Wherein,

Vn = ADC readings received from the neutral line

Vphase = ADC readings received from the phase line

[0024] To identify the voltage drift in the phase line Y, the transistor T3 is turned to the saturation mode and other transistors Tl, T2 and T4 are turned off. The microcontroller 106 receives the ADC readings from the phase line Y and the neutral line N and computes the variance for phase line Y. To identify the voltage drift in the phase line B, the transistor T4 is turned to the saturation mode and other transistors T1-T3 are turned off. The microcontroller 106 receives ADC readings from the phase line B and the neutral line N and computes the variance for phase line B. The microcontroller 106 compares the variance computed for each of the phase lines R, Y, B with the threshold value. The threshold value is in the range of 0.1-1.0 which is defined by the manufacturer of the electricity meter 100 during the production. The microcontroller 106 sends notification to indication means when the variance of the at least one phase line exceeds the threshold value. The notification includes at which phase line the variance exceeds the threshold value. For example, when the variance of the phase line R exceeds the threshold value then the notification includes the voltage drift detected in the phase line R. In one scenario, the variance detected in the all phase lines R, Y, B are same then the drifting detected in the neutral line, The microcontroller 106 notifies the indication means 108 about the neutral line drift in this scenario.

[0025] The microcontroller 106 is the essential component which controls for the overall operation of the electricity meter 100. The microcontroller 106 controls the controlling switches SW1-SW3 and T1-T4 during the diagnostic mode to identify the measurement uncertainty. The microcontroller 106 is configured to operate the electricity meter 100 in a diagnostic mode and the normal mode. The measurement uncertainty is measured in the diagnostic mode of the electricity meter 100. The microcontroller 106 allows the user to define the time interval at which the electricity meter 100 has to be operated in the diagnostic mode. Once, the diagnostic mode is initiated based on the predefined interval stored in the microcontroller 106, then the microcontroller 106 controls the operation of the controlling switches SW1-SW3 and T1-T4 sequentially and identifies the measurement uncertainty in the negligible time period and the normal operation of the electricity meter 100 resumed immediately. The microcontroller requires only a few seconds to perform the diagnosing operation hence the normal operation of the electricity meter 100 is not disturbed.

[0026] Advantages of the present embodiment are as follows:

1. The propose system and method uses non invasive method to identify measurement uncertainty, therefore no interruption in service.

2. Effortless continuous online monitoring, tracking and trending by the installed metering device, no additional cost of monitoring.

3. Early detection of measurement uncertainty, which can trigger realistic calibration alerts.

4. Error tracker and drift trending enable accurate planning and schedule re-calibration.

5. localizing the measurement uncertainty to functional / system blocks which enable the quicker servicing.

[0027] The present embodiment facilitates that the electricity meter 100 capable of detecting the measurement uncertainty without disturbing its normal operation. The electricity meter 100 includes the current measuring unit 102 and the voltage measuring unit 104 which are configured as shown in the figure 2 and figure 3 respectively. The controlling switches (SW1-SW3 & T1-T4) positioned in the current measuring unit and the voltage measuring unit is controlled by the microcontroller to identify the measurement uncertainty in each of the phase lines with respect to neutral line. The proposed electricity meter is cost effective. Since it uses only a few high precision electrical components to provide overall reliable operation of the electricity meter. Further, the electricity meter 100 includes the indication means 108 which stores logs of the identified measurement uncertainty along with its category such as voltage drift, current drift and a phase angle drift. The electricity meter 100 also locates where the measurement uncertainty is detected i.e. it also provides the information about at which phase line the measurement uncertainty is detected.

[0028] The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only. It is evident to those skilled in the art that although the invention herein is described in terms of specific embodiments thereof, there exist numerous alternatives, modifications and variations of the invention. It is intended that all such modifications and alterations be included insofar as they come within the spirit and scope of the invention as claimed or the equivalents thereof. Hence all variations, modifications and alternatives that falls within the broad scope of the appended claims comes under the gamut of the invention.

We claim:

1. An electricity meter (100) capable of detecting a measurement uncertainty without disturbing a normal operation, said electricity meter comprising:

a plurality of phase lines (R, Y, B) and a neutral line (N);

a plurality of current measuring means (CT1-CT4) which are positioned in a current measuring path (102);

a voltage measuring means (ADC) which is positioned in a voltage measuring path (104);

a plurality of controlling switches (SW1-SW3 & T1-T4) which are positioned prior to each of said current measuring means and said voltage measuring means; and

a microcontroller (106) which is configured (i) to selectively control at least one of said plurality of controlling switches at a predefined interval and (ii) to detect said measurement uncertainty in said electricity meter.

2. The electricity meter as claimed in claim 1, wherein said plurality of phase lines comprising a first phase line, a second phase line, and a third phase line, wherein said voltage measuring means connected to said plurality of phase lines and said neutral line through a plurality of voltage limiting circuit (Z1-Z4).

3. The electricity meter as claimed in claim 2, wherein in said current measuring path, said first phase line, said second phase line and said third phase line are positioned in parallel to each other and said first phase line, said second phase line and said third phase line are connected in series with said neutral line.

4. The electricity meter as claimed in claim 2, wherein in said voltage measuring path, said first phase line, said second phase line, said third phase line and said neutral line are positioned in parallel to each other.

5. The electricity meter as claimed in claim 2, wherein said microcontroller selectively controls at least one of said plurality of controlling switches (i) to measure a current passed through each of said first phase line, said second phase line, said third phase line and said neutral line by said current measuring means (ii) to measure a voltage passed through each of said first phase line, said second phase line, said third phase line and said neutral line by said voltage measuring means.

6. The electricity meter as claimed in claim 5, wherein said microcontroller receive and compare (a) said current and said voltage measured in said first phase line, said second phase line and said third phase line with (b) said current and said voltage measured in said neutral line individually.

7. The electricity meter as claimed in claim 6, wherein said microcontroller provides an alert when a difference between said current and said voltage measured in at least one of said plurality of phase lines and said neutral line is exceeds a threshold.

8. The electricity meter as claimed in claim 7, wherein said alert comprises a visual indication, an internal log or an audio indication.

9. The electricity meter as claimed in claim 1, comprises a plurality of phase detecting means (P1-P3) which are positioned between each of said plurality phase lines of said current measuring path and said voltage measuring path, wherein said plurality of phase detecting means detects a phase angle drift and communicates to said microcontroller.

10. The electricity meter as claimed in claim 1, wherein said uncertainty comprises a current drift, a voltage drift and a phase angle drift.