(Source: Sagiam / stock.adobe.com; generated with AI)
The future of modern electrical grids is akin to most large-scale, industrial, and enterprise systems; they are becoming highly digitalized to use electronic optimization systems to better deploy services, troubleshoot, and enhance efficiency. While smart electricity meters on homes are just one element of electricity grid modernization, they represent a crucial part of the equation.
At the end of 2023, the smart electricity meter market reached 43 percent globally,[1] and by 2033, some sources predict the number of global smart meters will grow to 3.4 billion.[2] These smart meters are for electricity, water, or gas, with the vast majority being smart electricity meters. A primary reason for this growth is the way smart meters benefit utility service providers by enabling data-driven decision-making, reducing time- and cost-intensive manual operator intervention, and accounting for the complexity of modern heterogeneous grid technology, such as solar, wind, and various energy storage methods.
A key element of these smart meter systems is the high accuracy of their current sensors. Legacy mechanical systems and current transformers fall short of meeting modern requirements of current sensing. Rogowski coil current sensors, on the other hand, are ideal for smart meter and smart grid applications. This blog discusses the three main methods of meter and grid current sensing and reveals why Rogowski coil current sensors are the go-to solution for modern smart meter and smart grid applications.
A home electricity meter system consists of electromechanical or electronic systems that continuously measure the instantaneous voltage and current from which the total energy usage—typically in kilowatt-hours (kWh)—is derived over time. For most residential applications, these meters are in line between the service conductors and the customer's electrical distribution system. For high-load applications, generally beyond 200 amperes of current load, a current transformer allows the meter to be located in a position other than the service conductors.
Historically, the electromechanical kWh meter is the most common type of electricity meter. These meters are an electromagnetic induction technology that uses the electrical conductivity of a non-magnetic disk to rotate the disk at a rate proportional to the electrical power conducted by the meter. This system has a voltage coil and a current coil that consume power separately, though this isn't registered by the meter. The voltage and current coils induce magnetic flux proportional to the voltage and current signal, essentially creating a two-phase linear induction motor with the power meter disk. A permanent magnet is used as an eddy current brake, which exerts a force proportional to the disk’s speed and allows for calibration of the disk rotation to correspond with the amount of power passing through the meter.
With current transformer meters, all of the previous system is in place. However, the service conductors are passed through a current transformer that couples with the service lines and extracts a smaller but proportional current to the current passing through the main service lines. This allows for a smaller, proportional current to be sent to the electromechanical kWh meter, which is calibrated to account for the exact proportional difference presented by the current transformer.
These current transformers are constructed using ferromagnetic cores. This presents some issues when attempting to extract highly accurate current signals across broad current ranges. Mainly, ferromagnetic core-based transformers experience nonlinear effects due to core saturation, meaning they are designed to operate within specific ranges of current levels determined by the physical characteristics of the transformer and the burden, which is the load connected to the secondary winding.
A Rogowski coil is a toroidal-like coil of conductive wire that encircles a current-carrying conductor. The current passing through the surrounding conductor induces a voltage in the Rogowski coil. The induced voltage is a function of both the current in the conductor and the AC frequency of the current. Using a simple equation, V = k*(dI/dt), where k is the constant derived from the coil's physical characteristics (length of winding, number of turns, loop size, etc.), we see that the voltage in the coil is dependent on the time-varying current. Using simple electronics that convert the induced voltage in the coil to a linear and frequency-independent output voltage, the output voltage can be used along with a calibrated scaling factor to derive the current carried by the primary conductor.
Unlike iron-core ferromagnetic current transformers, Hall effect, and fluxgate current probes, Rogowski coil current sensors are highly resistant to external electromagnetic interference, do not experience saturation when measuring high currents, are low weight and compact, and can be designed with an extremely wide dynamic sensing range. Moreover, these current sensors can be left unterminated while the current passes through the primary conductor without developing dangerous voltage levels (load-free operation). This is because Rogowski coils can be designed to develop millivolts per ampere, which means 1,000 amperes are required to develop 1 volt in the coil. The compact and flexibility of this coil design allow for a diverse range of integration methods and designs that facilitate installation.
Given the need for highly precise, compact, and flexible current sensors in modern electricity meters, Rogowski coil current sensors are the ideal technology for the future of smart meters. Yageo Pulse RC Series Rogowski Coil Current Sensors, in particular, are designed to exceed industry standards and ensure full compliance with the demanding requirements of smart meter and smart grid applications. (Figure 1).
Figure 1: Pulse Electronics Rogowski RC01/03/05 Coil Current Sensors meet the needs of modern energy management systems and are available in three different sizes, with sensitivity levels ranging from 100mV/kA to 600mV/kA at 50Hz. (Source: Mouser Electronics)
As smart grid and smart meter industries evolve, it's clear that there's a need for accurate and adaptable current sensing technologies, with legacy systems no longer meeting these demands. However, Rogowski coil current sensors provide a solution that offers flexibility, precision, and durability. These sensors can handle a broad range of current and offer resistance to electromagnetic interference that, when combined with their ease of integration, make them the right option for the next generation of energy management systems.
Principal of Information Exchange Services: Jean-Jacques DeLisle Jean-Jacques (JJ) DeLisle attended the Rochester Institute of Technology, where he graduated with a BS and MS degree in Electrical Engineering. While studying, JJ pursued RF/microwave research, wrote for the university magazine, and was a member of the first improvisational comedy troupe @ RIT. Before completing his degree, JJ contracted as an IC layout and automated test design engineer for Synaptics Inc. After 6 years of original research—developing and characterizing intra-coaxial antennas and wireless sensor technology—JJ left RIT with several submitted technical papers and a US patent.
Further pursuing his career, JJ moved with his wife, Aalyia, to New York City. Here, he took on work as the Technical Engineering Editor for Microwaves & RF magazine. At the magazine, JJ learned how to merge his skills and passion for RF engineering and technical writing.
Sources
[1] https://iot-analytics.com/smart-meter-adoption/ [2] https://transformainsights.com/news/global-smart-meters-2033
Pulse Electronics is a leader in technology, design, and manufacturing of passive electronic components, including power and networking magnetics, current sensing, cable harnesses, power supplies, antennas, connectors, and inductors, as well as a complete offering of power transformers, RF components and ethernet transformer products. With both catalog parts and custom design capability, Pulse is a complete source for electronic OEMs and CEMs worldwide.