Schneider Electric Usa, Inc.

Kurt H Copley

Ronald W Carter

Donovan Eugene Wilkerson

A method of measuring the total harmonic distortion in an electrical distribution system. The distribution system is sampled regularly to generate a set of data. The data is filtered using a narrow band filtering algorithm to measure the energy in fundamental and other harmonic frequencies. Due to the filtering, the energy in harmonic frequencies can be measured without interference from broadband noise, which provides an improvement in the measurement of total harmonic distortion at low current or voltage levels. A method is provided to sum the energy in identified frequencies in a multi-pass configuration, such that only a subset of all monitored frequencies are filtered and summed in each pass, with the balance being filtered and measured in subsequent passes. After all subsets are measured, the total harmonic distortion is calculated.

Method for measurement of total harmonic distortion

A system and methods for determining points for an algorithm to calculate the frequency of a waveform measured from a monitoring device. Data points are measured from the waveform. A last point of interest from the previous cycle of the waveform is referenced. Four points of interest at equally spaced phase angles from the current cycle of the waveform are determined by calculating the average of the data points around each of the respective equally spaced phase angles of the current cycle of the waveform. The average value of the points of interest in the current cycle is subtracted from the four points of interest and the last point of interest from the previous cycle to compensate for DC bias. A frequency of the waveform is determined based on the determined four points of interest of the current cycle and the last point of interest from the previous cycle. The correction factor for determining sample frequency may be reduced for subsequent cycles in order to increase stability.

System and method for frequency measurement based on quadratic forms

A system and methods for synchronizing quantized sampled data in a monitoring device. A variable frequency output signal is coupled to an analog to digital converter. A fixed frequency clock is coupled to the analog to digital converter. The analog to digital converter samples the output signal at a fixed frequency to produce high speed samples. A group of initial high speed samples is stored from the analog to digital converter over a fixed window of time. The group of initial high speed samples is interpolated to produce a group of fewer low speed samples from the initial group of high speed samples over the fixed window of time. The group of low speed samples is stored as a representation of the variable frequency output signal.

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Smyrna, TN, United States of America

Kurt H Copley