Harmonic Distortion and Distribution Transformer Thermal Risk in Low-Voltage Networks: Feeder Impedance Sensitivity for Sustainable Renewable Energy Integration

The increasing penetration of distributed energy resources (DERs) in low-voltage networks is central to the clean energy transition but introduces coupled challenges in voltage regulation, harmonic distortion, and distribution-transformer operation that impact grid sustainability and asset longevity. This paper isolates feeder impedance as a controlled variable and evaluates whether remote-network power-quality severity and transformer consequence follow the same sensitivity trend. A time-domain model used a factory-matched 200 kVA, 11 kV/420 V Dyn11 transformer with 40% DER connected at remote Node S3. The DER current contained prescribed fifth, seventh, eleventh, and thirteenth harmonics, while the LV feeder resistance and inductance were co-scaled from 0.5 to 2.0 pu. Across the DER-connected sweep, Node S3 line-to-line RMS voltage increased from 420.45 V to 428.95 V, and the voltage-rise magnitude increased from 3.03 V to 11.55 V. Selected-order Node S3 VTHD increased monotonically from 1.104% to 1.395%. Baseline-corrected harmonic transfer impedance also increased at every assessed harmonic, supporting a feeder-impedance-driven voltage-response mechanism. In contrast, transformer loading remained within 14.44–14.52%, total transformer loss within 350.26–350.93 W, hot-spot temperature within 38.229–38.246 °C, and common-baseline relative aging within 0.2863–0.2871. The results demonstrate that feeder weakness can materially increase remote-node voltage and harmonic sensitivity without producing a corresponding increase in transformer thermal severity. Network voltage response and transformer consequence should therefore be assessed as related but non-equivalent engineering domains. By separating power quality management from transformer thermal risk, distribution utilities can avoid premature asset replacement, enabling targeted, resource-efficient investments that support sustainable grid planning and long-term renewable integration (SDG 7 and SDG 9).