This paper reviews the design and implementation of hardware and software tools for nonintrusive electrical load monitoring. Estimates of spectral content in measured waveforms can be used to determine in real time the operating schedule of loads at a target site. Techniques for transient event detection are reviewed. These techniques can detect the turn-on and turn-off transients of individual loads, and can be used to easily determine the energy usage of loads that draw constant power in steady-state operation. Techniques for monitoring the power consumption of smoothly varying loads (e.g., variable speed drives) using spectral estimates are also discussed.

This paper describes two hardware prototypes and estimation schemes for determining the parameters of a simple, physically based, point-of-use electric utility model using transient measurements. Parameters of the utility model are estimated using data collected by the prototypes. Frequency-dependent effects observed in previous work in this area are modeled. Performance of the techniques given is demonstrated by comparison of measured and predicted line voltage distortion during current transients created by several loads. Index Terms-Estimation, power distribution testing, prediction methods. I. BACKGROUNDF ROM A SERVICE outlet, the electrical utility can be approximated as a sinusoidal voltage source in series with an inductor and a resistor. In a commercial or industrial building, impedances seen at the "user interface" arise predominantly from an upstream transformer, protection circuitry, and cabling. Harmonic currents generated by loads flow through these impedances, creating voltage drops that result in a distorted voltage waveform at the service outlet.In [1], an interesting technique for determining the local apparent impedance of the electrical utility service is presented. The impedance is identified by briefly closing a capacitor across the electrical service at a precise point in the line voltage waveform. The shape and decay of the transient current in the resulting RLC circuit can be used to estimate the line impedance.In this paper, the technique in [1] is reformulated in two point-of-load impedance characterization and voltage distortion prediction systems. The first system (method A) uses the RLC transient excitation technique from [1], but features a digitally programmable test capacitor, a phase-programmable switch, and a data collection interface. The second system (method B) consists of a programmable current source, providing more flexibility in test transients. The two systems, and their associated estimation procedures, share a point-of-load model of the electric utility. This model, motivated by theory, accounts for the measured increase in resistance as a function of test transient frequency observed in [1] and [2]. Ultimately, the model and estimated parameters are used to predict voltage distortion from transient currents.

No abstract