Voltage between 2 phases lower than others, while phase voltages equal

A measurement anomaly was observed in a company's electrical grid where the voltage between two phases (U31) appeared lower than other phase-to-phase voltages, despite phase-to-neutral voltages being nearly equal. The issue was initially unexplained by phase shift or lower phase voltage. The user shared measurement data via a link and later confirmed with the network analyzer manufacturer that the anomaly was due to a firmware bug requiring an update. Analysis of the measurement graph revealed inconsistent representation of voltages, with some traces overwritten or mis-scaled by the instrument. Additional explanations for voltage imbalance included unbalanced three-phase equipment such as induction motors with unequal winding reactance, large single-phase loads causing voltage drops, switching surges from heavy loads, and unequal impedances in the power distribution system. Firmware update was recommended to correct measurement display errors and obtain accurate phase-to-phase voltage readings.
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