MONITORING & METERING


SMART SOLUTIONS FOR MONITORING ENERGY


With smart meters providing utility companies and end users with a huge range of benefits, Cosimo Carriero, staff field applications engineer at Analog Devices, examines the technology and looks at advances in field diagnosis


A


fter more than one hundred years of energy transportation with minimal technological


variation, electricity distribution networks have recently seen a dramatic transformation. In a world dominated by technological evolution, the energy sector has evolved to include renewable energy sources such as wind and solar. We also have new challenges such as the bidirectional flow of energy, intermittence in generation from renewable sources, distribution of electrical power, and noise emission on power lines, resulting in potential network stability issues. To guarantee continuous and quality service to


end customers, energy distribution companies are incorporating smart meters to allow for real-time network diagnostics and immediate fault detection. This technology provides utility companies and end users with a multitude of benefits. So, in this article, I will illustrate smart meter fundamentals and advancements in field diagnostics.


THE SMART ELECTRICITY METER The smart electricity meter is a fundamental component of the energy distribution network. In addition to monitoring energy consumption, a smart meter can collect data on the quality of the power supplied. For example, it can measure the reactive energy, the total harmonic distortion, the harmonic content, the presence of voltage surges and transients, and changes in frequency, all of which are indicators of the state of the network. But how does an electricity meter work? Figure 1, right, shows a block diagram with the main components, both for a single-phase system


and for a 3-phase system electricity meter. In a smart meter, the basic electrical qualities


are derived from the voltage and current measurements. These measurements are processed by a special analog front end (AFE) and supplied to the microcontroller, which displays them or makes them available for the communication node for remote transmission. A power management unit completes the structure.


SENSORS TO MEASURE VOLTAGE AND CURRENT One critical aspect of an electricity meter is the measurement of current. Unlike voltage measurement, which may present only small deviations from the nominal value, the current has a very wide dynamic range, from a few milliamps up to hundreds of amps, and it must be measured with the utmost precision over the entire range. While a simple resistive divider, and more rarely a transformer, is used for voltage measurement, he sensors used to read the current can vary. Generally, the following four types of sensors are used: the shunt, the current transformer (CT), the Rogowski coil, and the Hall effect sensor. Each of these sensors has


advantages and disadvantages. For example, the shunt, widely used in domestic meters, is economically advantageous and practical. The biggest drawback of the shunt is Joule effect heating, which limits its use at high currents. In comparison, the current transformer supersedes


the limitations of the shunt in terms of maximum current and is intrinsically isolated, which is highly advantageous. The CT comes in the form of a toroid, and its primary winding is represented by the conductor, in which the current that you want to measure flows through the ring. The secondary winding is wound on a ferromagnetic material, and the number of turns establishes the transformer turns ratio. Compared with the shunt, the CT has a higher cost and a larger footprint. A significant limitation of a current transformer is its ferromagnetic core which, if saturated, seriously compromises the operation of the smart meter. Saturation can result from a DC offset in the AC, a high current peak, or an external magnetic field such as that generated by a permanent magnet. Because of this limitation, systems that use the


Figure 1. Block diagrams of single- and 3-phase smart electricity meters


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