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Discover how the next generation of smart meters works!

Discover how the next generation of smart meters works!

[Introduction]For more than a hundred years, energy delivery has changed little in terms of technology, but in recent years, the distribution network has changed dramatically. In a world dominated by technological evolution, the energy sector has grown to include renewable energy sources such as wind and solar. We face new challenges such as bidirectional flow of electrical energy, intermittency of renewable energy generation, power distribution, noise on power lines, etc., which can lead to grid stability issues.

To ensure continuous and high-quality service to end customers, distribution companies are turning to smart meters to enable real-time diagnosis of the grid and instant detection of faults. This technology brings many benefits to power companies and end users. This article presents the basics of smart meters and advances in on-site diagnostics.

smart meter

Smart meters are a fundamental part of the distribution network. In addition to monitoring energy consumption, smart meters can also collect data on the quality of power supply. For example, it measures reactive energy, total harmonic distortion, harmonic content, the presence or absence of voltage surges and transients, and changes in frequency, all of which are indicators of grid status. But how does an electricity meter work?

The block diagram in Figure 1 shows the main components of a single-phase system and a three-phase system meter.

Discover how the next generation of smart meters works!

Figure 1. Block diagram of single-phase and three-phase smart meters

In smart meters, basic power quality is obtained from voltage and current measurements. These measurements are processed by a special analog front end (AFE) and provided to a microcontroller, which displays the results or provides them to a communication node for remote transmission. The complete structure also includes a power management unit.

Sensors that measure voltage and current

A key aspect of an electricity meter is current measurement. In voltage measurements, the measurement may have only a small deviation from the nominal value, but current measurement is different, the current has a very wide dynamic range, from a few milliamps to hundreds of amps, the whole range must be as high as possible Measure with accuracy. Voltage measurements can be made using a simple resistive divider (and less often a transformer), but there are many types of sensors used to read current. The following four types of sensors are generally used: shunts, current transformers (CTs), Rogowski coils, and Hall effect sensors. Each of these sensors has advantages and disadvantages. For example, shunts are widely used in household electricity meters for economical advantages and practicality. The biggest disadvantage of a shunt is the Joule heating effect, which limits its use at high currents.

In contrast, current transformers remove the shunt limitations in terms of maximum current and are inherently isolated, which is very beneficial. CTs are provided in a toroidal form with a primary winding represented by a conductor through which the current to be measured flows. The secondary winding is wound on a ferromagnetic material, and the number of turns determines the transformer turns ratio. Compared to shunts, CTs are more expensive and larger in size. A significant limitation of current transformers is their ferromagnetic core, and if saturated, the operation of smart meters can be severely affected. Saturation can be caused by DC bias in AC, high current peaks, or external magnetic fields such as those produced by permanent magnets. Due to this limitation, systems using current transformers must provide shielding or other protection mechanisms to avoid tampering.

Hall-effect sensors have excellent frequency response and can measure high currents. However, these advantages are diminished by high temperature drift; to obtain the required accuracy, system calibration must be performed at multiple points.

Like current transformers and Hall effect sensors, Rogowski coils are inherently isolated. A Rogowski coil is an Inductor that is mutually coupled to a conductor through which the current to be measured flows. Magnetic coupling occurs through an air core, so it does not introduce saturation problems common to ferromagnetic materials. The characteristic of Rogowski coils is that the signal produced by the sensor is proportional to the derivative of the current, so an integrator is required to reconstruct the original signal.

In order to achieve a wide dynamic range and high linearity, as well as being able to measure very high currents, current sensing with Rogowski coils requires the use of a stable integrator. In addition, Rogowski coils are particularly susceptible to external fields that allow end users to manipulate power measurements.

Introducing mSure technology for the next generation of smart meters

A smart meter must be able to perform its function accurately for a relatively long period of time, possibly more than 10 years. Good design and the stability of silicon electronics allow it to maintain a high level of precision for many years. However, environmental events such as lightning, current spikes or voltage transients can permanently alter sensor performance. This effect is difficult to detect without advanced diagnostic systems. mSureĀ® is a new meter diagnostic technology developed by Analog Devices that checks the status of the measurement chain in real time and protects sensors from environmental influences. mSure technology is unaffected by the environment and can be diagnosed with or without human manipulation.

The working principle of mSure technology is shown in Figure 2. Standard electricity meters operate in open loop without a feedback path. The current and voltage are converted by the sensor, there is a processing chain that adds gain, and finally an analog-to-digital conversion to extract the data directly in the digital domain. Each device contributes to the total error; off-line calibration is used to compensate for the initial error and to ensure that the meter accuracy remains within specifications for a particular class.

Discover how the next generation of smart meters works!

Figure 2. Comparison of open-loop and closed-loop systems with mSure technology

Once a standard meter is installed in the field, there is only one way left to test its accuracy, and that is to physically remove it and send it to a lab for testing. A less invasive alternative is to verify the performance of production batches, but this approach is costly. Compared to standard meters, meters with mSure technology can verify accuracy in real-time with a more complex closed-loop system in the field, as shown in Figure 2. The closed loop system consists of adding a voltage reference module that generates a stable and very accurate signal to inject into the sensor. This signal travels through the entire measurement chain and is picked up by the detection module. The entire signal chain is monitored in real time, and any errors (such as gain, drift, etc.) are captured, enabling continuous calibration to adjust for these errors. Additionally, one of the biggest advantages of mSure technology is fraud detection. Most tampering involves changing the gain of the measurement chain, so unlike open-loop systems, mSure is able to detect this change immediately.

mSure is non-intrusive and can be activated while the meter is running. To ensure accurate readings, an appropriate module detects and subtracts the contribution of the mSure device to the final energy measurement. Therefore, the accuracy of the meter depends on the accuracy of the reference voltage module. By definition, the accuracy of a voltage reference module is better than the accuracy of the sensors used in the system.

The automatic calibration function can be activated at any time. The calibration data consists of the gains of the current and voltage measurement chains. mSure technology can extract this data with high accuracy without resorting to expensive calibration benches. To perform a self-calibration, first connect the meter to a voltage source. Whether to add load is optional.

Once a smart meter with mSure technology is installed in the field, you can check the meter’s accuracy continuously or at predetermined intervals. If the meter has accuracy drift, the calibration data can be corrected to make the energy count accurate. To date, government regulations have not allowed the calibration data of standard electricity meters to be changed in the field. With mSure technology, power companies will be able to intervene in a timely manner when needed; if the intervention time is longer, there will be an accurate estimate of the power difference.

The ADE9153B and ADE9322B are mSureĀ®-embedded energy metering ICs with sensor monitoring and self-calibration for Analog Devices’ next-generation smart meters.

Energy Analytics Studio

The mSure product portfolio includes Energy Analytics Studio (EAS). EAS is a cloud analytics service that supports mSure technology that verifies the health of each meter (health monitoring), ultimately protecting the revenue of power companies. The mSure Manager software runs on the system microcontroller and reports data related to meter parameters. The reporting frequency can be determined by the operator. mSure Manager allows you to check the status of a single meter, of all meters in a geographic area (for example, those affected by some unusual weather event), or of all meters of a production batch.

Discover how the next generation of smart meters works!

Figure 3. Edge-to-cloud solutions for utility companies

in conclusion

The innovative mSure technology enables real-time diagnostics of on-site electricity meters. Combined with Energy Analytics Studio, it monitors meter health without intervention in the event of an actual failure and prevents fraud. The benefit to the utility is to optimize meter management, reduce losses, save costs, and extend the average lifespan of the meters.

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