Power Electronics

Energy Metering May Link Grids and Chips

For ages, utility companies have relied on mechanical watt-hour meters to measure their customers' energy usage. But in recent years, spurred on by deregulation and new technology, these companies have increasingly turned to electronic designs for their energy meters. There are many compelling economic reasons for doing so.

In parts of the developing world, where many new residential customers are being connected to the grid, the cost of the meter itself is a prime concern. For these markets, a basic electronic meter can be built for less money than a mechanical meter. This type of electronic meter typically consists of a current-sensing shunt or transformer, an energy metering IC, and a stepper-motor display or mechanical counter. The IC measures voltage and current, and generates a pulse output proportional to power, which drives the display. These meters are sometimes called stepper-motor display meters.

However, the greater lure of electronic energy metering stems from its versatility and precision. When the stepper-motor display is replaced with an LCD display, which currently costs more than a stepper-motor display, the energy meter is empowered to measure and output a variety of energy-related data. The so-called LCD display energy meter can record energy usage at different times of day or even different forms of power (ex. real versus reactive) to enable multi-rate billing.

But those benefits are the tip of the metering iceberg. An electronic meter can provide an order of magnitude improvement in measurement accuracy over that of a mechanical meter, while lowering the meter's power consumption by two orders of magnitude. Another plus is the electronic energy meter's ability to detect and guard against meter tampering.

Because some type of compute engine is required for various calculations, the LCD display energy meter is inherently programmable. Therefore, a basic hardware design can be reconfigured in software for different applications and calibrated with ease. Another major benefit is the option of designing in automatic meter reading (AMR), the ability to collect data over an RF or power-line link.

Although these advanced function meters now cost more than a mechanical meter, this discrepancy should disappear as semiconductor vendors and LCD display makers steadily reduce the cost of their metering ICs and displays. (More details on energy metering ICs will be presented in an upcoming “Analog Feedback”.)

For many applications, the higher cost of the full-function meter is already justified by its performance. Utilities in the Unites States, Europe and other areas with established infrastructure are adopting the LCD display meters, both in industrial and residential applications. In these applications, multi-rate billing and AMR are often cited as the key drivers of electronic energy metering.

According to the vendors that make energy metering ICs, around 40 to 50 million electronic energy meters were installed worldwide last year. That figure represented about one-third of the total for all new meters (both mechanical and solid-state). Note that most of the electronic models were installed outside the Unites States. However, the growth for electronic metering is high as the costs keep coming down. Before long, most of the new meters being installed will be electronic.

This trend has many implications. For power supply and system designers, the impact of electronic energy metering may be how it raises awareness of power-quality issues. Metering studies could influence the development of performance standards for power supply noise or efficiency.

At some point, energy management at the grid level may even converge with power management at the system- or pc-board level. One aspect of that could be “sub-metering” — extending energy measurement to the individual operating units within a large facility. This concept can be extended to encompass the measurement of energy consumed by a single piece of equipment. Submetering might lead to some form of interactive power management involving the ac lines and the equipment on those lines. We can only imagine the added complexity that this might bring to power system design.

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