How WB-MAP calculates line-to-line voltage

WB-MAP metering chips measure RMS phase voltages and the angles between them. Firmware calculates line-to-line voltages trigonometrically. For strictly sinusoidal inputs, this is mathematically equivalent to direct line-voltage measurement, including unbalanced phase amplitudes and angles.

Harmonic distortion can introduce additional error. Manufacturer tests with an Energoforma 3.3 programmable three-phase generator found that, at harmonic distortion up to 10%, the displayed line-voltage error stayed below 0.5%, typically 0.2–0.3%. In an extreme test with 15% distortion and an A–B angle of 45° rather than 120°, Ua–Ub error remained below 1.5%.

These results concern the batches discussed by the source. Older batches and firmware could have additional errors associated with ERRMAP0007, ERRMAP0010 and ERRMAP0012. Consult the known issues.