K2U-NODE: DESIGN AND VALIDATION METHODOLOGY OF AN OPEN-SOURCE TWO-GENERATION DEVICE FOR THREE-PHASE VOLTAGE-UNBALANCE MONITORING, K2U-NODE: ПРОЕКТИРОВАНИЕ И МЕТОДИКА ВАЛИДАЦИИ ДВУХПОКОЛЕННОГО УСТРОЙСТВА С ОТКРЫТЫМ ИСХОДНЫМ КОДОМ ДЛЯ МОНИТОРИНГА НЕСИММЕТРИИ ТРЁХФАЗНЫХ НАПРЯЖЕНИЙ, K2U-NODE: UCH FAZALI KUCHLANISHLAR NOSIMMETRIKLIGINI MONITORING QILISH UCHUN OCHIQ KODLI IKKI AVLODDAN IBORAT QURILMANI LOYIHALASH VA VALIDATSIYA METODIKASI

<jats:p>This article presents the design and validation methodology of the open-source two-generation K2U-Node device intended for voltage-unbalance monitoring in three-phase electrical networks. The theoretical limitations of determining the negative-sequence voltage unbalance factor (K₂U) using only phase-voltage RMS magnitudes are analyzed. The Gen-1 device, based on an ESP32 and three PZEM-004T v3.0 modules, is proposed for preliminary screening and distributed monitoring of voltage unbalance. The Gen-2 device, based on the ATM90E32AS metering IC, measures both voltage magnitudes and phase angles, enabling calculation of the complex symmetrical components and the K₂U factor. Numerical examples demonstrate that angular unbalance can produce a significant K₂U value even when all phase-voltage magnitudes are equal. A three-stage calibration and validation methodology is proposed, together with 10-minute aggregation of measurement results in accordance with GOST 32144-2013 and IEC 61000-4-30 requirements. The proposed solution provides a promising basis for multi-point power-quality monitoring, identification of voltage-unbalance sources, and technical assessment of distributed energy facilities.</jats:p>