Wave Tracking Simplifies Load Harmonic Measurements
Microstar Laboratories announced the Wave Synchronization Module software, now available with DAPtools Standard software. This module provides a real-time software-oriented approach to the problem of aligning data streams to the local power system frequency, obtaining greatly improved load harmonic measurements by avoiding data corruptions that are otherwise caused by sampling rate misalignment or power frequency drift. This software runs on xDAP data acquisition systems and is hosted by the DAPL 3000 embedded operating system, included with the DAPtools Software.
|Wave Synchronization Module aligns measurements to local power frequency. (Electrical power transformer in high voltage substation: emel82/Shutterstock.com)|
Bellevue, WA – The Wave Synchronization Module (WSM) software from Microstar Laboratories, Inc., maker of Data Acquisition Processor (DAP) systems for PC-based high-performance measurement applications, applies a mathematical alignment of data streams to power system cycles at the prevailing frequency, making harmonic analysis for power distribution systems as easy as it gets.
Hazards for Load Harmonic Measurements
Power harmonics in loaded power distribution systems occur because of nonlinearity -- in magnetic windings, switching power supplies, and so forth. Distortions become worse as feeder voltages droop, and can result in costly penalties or restrictions on service. The first step to controlling harmonic distortions is to measure them.
A standard technique is to measure 4096 voltage points, spanning 10 power cycles, and then apply an FFT analysis with power spectral density post-processing. This supplies enough data to distinguish the harmonic frequencies from each other and from random noise events. However, if this data set doesn't match an exact number of power system cycles, the phenomenon of spectral leakage attenuates sharp harmonic lines of the spectrum into smeared wedge shapes, with variously reduced amplitudes.
Even if you could configure the data acquisition clocking to perfectly match the power system frequency, the short-term operating frequency of the power system routinely drifts 0.1% or more from nominal frequency, particularly under stressed conditions when accuracy is most needed. These disturbances are enough to shift some of the harmonics to the wrong locations in the calculated power spectrum. The DSP technique of windowing can be used to mitigate this problem somewhat, but at the cost of further attenuation and smearing of the harmonic terms. Using this conventional approach, a net measurement error of +/-20% through the first 40 harmonics might be considered success.
The Wave Synchronization Module Solution
All of the above problems result because the data acquisition system operates at one frequency while the power system operates at another. The harmonic analysis requires strict alignment. That is exactly what the Wave Synchronization Module gives you. You configure it for the number of samples you want, equally spaced per wave cycle, and that is exactly what you get, regardless of frequency drift. Once your data set aligns with the power cycles, you don't get the leakage distortions, you don't need the windowing, and you get maximum accuracy. No special equipment is required beyond the minimum necessary to observe the voltage waveform.
If you just want results, and don't want to deal with some kind of complicated software environment for the FFT power spectrum analysis, you have additional options to stream your raw data sets to embedded processing commands, so that the spectral analysis is done before delivering data to your application. Or, if you want to be even more elegant and selective, you can isolate and deliver only the relevant FFT power spectrum terms corresponding to the harmonic frequencies.
The Wave Synchronization Module is available with the purchase of DAPtools Standard software with a new xDAP data acquisition system from Microstar Laboratories, or as a software upgrade for an existing xDAP system. The DAPtools Standard software includes the DAPL 3000 system, the processing engine that controls all of the real-time processing within the embedded xDAP environment. The current DAPtools release supports Windows 10, Windows 8, Windows 7, Windows XP, and Windows Server on the PC host system. Also included with the DAPtools Standard software are modules for digital countermeasures to aliasing, and various data management, transform, and filtering operations.
The Wave Synchronization Module is available now. Contact Microstar Laboratories to obtain a copy for your xDAP system. The one-time license fee for the DAPtools Standard package, with the Wave Synchronization Module, is $195.00 USD.
The Wave Synchronization Module from Microstar Laboratories provides a modern, DSP-based approach that can align data samples to a power system frequency, enabling straightforward and accurate measurement of harmonic distortion. The results are better than you can get using conventional measurement methods, such as specialized frequency-tracking clock-oscillator hardware or DSP windowing compensation, and the method is simpler to configure and apply.