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Reactive energy measurement made simple

Ballast lighting, computer monitors, air conditioners and industrial machines are welcome additions to our lives, but come with an additional burden. Utilities are concerned that inductive and capacitive loads are unaccounted for in KWh-only billing using traditional electromechanical meters, especially in a competitive, deregulated environment.

Analog Devices’ new energy metering ICs – the ADE7753 and ADE7758 – now allow utility companies to obtain accurate energy usage information more easily than ever before. Reactive energy, caused by nonlinear loads, requires energy suppliers to supply more volt-amps to customers than they can measure with a conventional watt-hour (active energy) meter. The ability to measure reactive energy enables utility companies to prevent revenue loss and improve power-generation capacity management.

Figure 1: Simplified Functional Block Diagram of ADE7758

Like all of Analog Devices’ energy ICs, the ADE7753 and ADE7758 are based on ADI’s industry leading, high-resolution analog-to-digital converter (ADC) technologies combined with a fixed-function DSP. The DSP performs all the necessary energy measurement calculations, allowing a low-cost microprocessor to be used for data management and supervisory functions. This architecture simplifies meter designs that previously relied on microprocessors to perform complex computations. The reduction in extensive code development significantly reduces cost and time-to-market.

About the ADE7758/ADE7753

The ADE7758, which features second-order sigma-delta ADCs, is designed for mid-range three-phase energy meters. For each phase, the chip measures reactive, active and apparent energy; as well as rms voltage and rms current. These measurements are accessed via a serial interface that allows a fully automated digital calibration. The ADE7758 interfaces with a variety of sensors, including current transformers and di/dt current sensors, such as Rogowski coils. Like other products in the ADE family, the ADE7758 provides accurate active energy measurements with less than 0.1 percent gain error over a current dynamic range of 1000:1. Its reactive energy measurement also surpasses the Class 2 IEC61268 accuracy requirement of VAR-hr meters.

Figure 2: Simplified Functional Block Diagram of ADE7758