From Energy Audits to Monitoring Megawatt Loads: A Flexible and Deployable Power Metering System

Abstract

The U.S. Federal Government and commercial partners have identified a critical gap in today's measurement technology—the ability to accurately, inexpensively, and wirelessly submeter building electricity usage at the circuit-level. Such metering technology would enable building owners, operators, and occupants to characterize and curtail electricity use in buildings—a major cost and source of carbon emissions today. Existing circuit-level metering systems are too costly to deploy, due to difficult installation or cumbersome calibration processes, too inaccurate, due to an inability to faithfully calculate power from synchronized current and voltage channels, or too unreliable, due to a strong dependence on a frequently lossy wireless channel. We propose Triumvi, a standalone, self-powered, non-contact, true-power metering system to help make circuit-level metering affordable, accurate, and reliable—in short, usable. In a splitcore current transformer form factor, Triumvi harvests energy to power itself, monitors current and voltage, calculates power, encrypts data, and wirelessly transmits the results. Our prototype can sustain a sample rate of nearly 0.5 Hz when the load draws at least 360 W and exhibits an average error of 4.3% over a load power draw range of 150-600 W. Triumvi also supports rapid installation, incremental upgrades, metering three phase and high current loads, charge sharing between between meters, and current waveform analysis, creating a highly flexible metering system capable of energy audits, industrial equipment monitoring, and many applications in-between.