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HARMONIC MEASUREMENTS

The subject of power quality has gained tremendous attention over the past decade. Harmonic currents generated in the distribution systems due to the growing use of non-linear load equipment and new technologies in buildings pose a new, serious problem for electrical engineers, where power quality is a prime concern. The trouble is because of some nonlinear loads showing different current waveforms when supplied by a distorted voltage. It is widely accepted that careful planning and design can minimise the risk of harmonic-related losses in electrical systems. In broad terms, power quality refers to the degree to which voltages and currents in a system represent sinusoidal waveforms. Harmonics have become a serious issue for electrical engineers around the world following the extensive use of electronic appliances. It is an accepted fact that the quality of electrical power in commercial and industrial installations is decreasing seriously.

 

Several conclusions useful in the design of electrical distribution systems are yielded by an assessment of the harmonics found in an electrical distribution system. In harmonic measurements, a preliminary survey to determine where the significant amounts of harmonic currents or voltages existed in the distribution system is performed by comparing readings taken with true root-mean-square multimetres and averaging multimetres. Facilities that appeared to have significant levels of harmonics present can be analysed from these measurements and subsequent calculations, with a power analyser that could record waveforms and give the spectrum and magnitude of harmonics.

 

For a number of reasons, harmonic measurements are an important part of the overall investigation of an electrical system. These measurements must be used, most importantly, to characterise the level of harmonic generation for the existing nonlinear loads. To accomplish this, voltage and current harmonic levels are measured at multiple sites by elensol. System conditions at the time of the measurements have to the accurately documented so that the results can be used to verify analytical results. One of the specific objectives of the harmonic measurements is the determination of the harmonic generation characteristics of the nonlinear loads, which is done by performing current measurements at a variety of locations within the facility. Three-phase measurements are made so that characteristic and non-characteristic harmonic components can be determined.

 

Another specific objective of the harmonic measurement is the determination of the system response characteristics for particular conditions, where voltage measurements are used in conjunction with the current measurements to characterise system response for specific system conditions. The basis for verifying the analytical models are these conditions. Third specific objective of the harmonic measurement is the determination of the background harmonic voltage and current levels. The measurements are typically performed by elensol in order to assure that adequate data is collected to characterise the system operation and for verification of the analytical models.