Pacific Power Source, Inc., a manufacturer of AC Power Sources and Power Conversion Equipment has published an informative white paper titled "Line to Line Voltage Considerations with Line Injected Harmonics." The note, which clarifies why various harmonics injected on individual phases of a waveform may produce unexpected results when observed Line to Line rather than Line to Neutral, is available for free download from the company's website at: http://www.pacificpower.com/infocenter/white_papers.html
The white paper describes how engineers can use Pacific Power's AMX Series power source to synthesize waveforms for applications such as simulating AC power line harmonics and other power perturbations. It outlines how engineers can use the company's UPC 32 Programmable Controller with the Harmonic Analysis and Synthesis (HAS) option, which permits specifying the waveform and amplitude of each phase of a signal independently and creating harmonics through the 50th order. It also illustrates how the company's UPC Software is used to create custom waveforms of varying harmonic content and phase angles. These synthesized waveforms can then be downloaded to the AMX power source for execution. The white paper is extensively illustrated with waveform captures that demonstrate the differences in power line signals that become apparent when observing results as line to neutral rather than as line to line.
The white paper explains why the calculation of line to line results, either in harmonic or transient conditions, may not be intuitive. In any three-phase application, a disturbance placed on a single vector will always affect both adjacent phase to phase vectors. Careful planning and a thorough understanding of vector addition and line interaction are necessary to fully appreciate the power of Pacific Power's arbitrary waveform capabilities.
These capabilities allow creating line to line results where the integer harmonics can be forced to add to the peak of the waveform. Pacific Power's HAS option also offers the ability to specify the starting phase angle of the harmonic in addition to the harmonic order and percent harmonic. By using three different waveforms that have the same harmonic content but which are offset by the normal 120 degree phase angle, the zero crossing of the harmonic order is moved off the 120 degree point of the fundamental.