Field Measurement and Experimental Investigation of Harmonic Resonance, Voltage Rise, and Protection Miscoordination Impacts from Clustered Rooftop Solar PV Integration on a Weak Nigerian 11 kV Distribution Feeder
Keywords:
rooftop solar PV, harmonic resonance, voltage rise, protection coordination, weak distribution feederAbstract
Clustered rooftop solar photovoltaic (PV) systems are spreading rapidly across affluent Nigerian neighbourhoods, yet their interaction with the country's characteristically weak, long, radial 11 kV feeders remains almost entirely unquantified by field evidence. This study reports a comprehensive experimental investigation conducted on a live 11 kV distribution feeder in Yenagoa, Bayelsa State, hosting approximately 1.86 MWp of clustered rooftop PV. Class-A power quality analyzers were deployed at five feeder points for a twelve-week campaign, complemented by secondary-injection testing of the feeder's inverse definite minimum time (IDMT) overcurrent relays and synchronized solar irradiance logging. Voltage total harmonic distortion rose from a baseline of 1.8 % to 7.4 % at the feeder extremity during peak injection, breaching IEEE 519 limits, while current THD reached 19.7 %. Frequency-response sweeps identified a parallel resonance near 320 Hz that amplified fifth- and seventh-order harmonics by up to 2.6 times. Measured voltage rise correlated strongly with irradiance (R² = 0.93), producing sustained excursions above the +5 % statutory limit at three measurement points. Secondary injection demonstrated that PV infeed collapsed the 0.3 s grading margin between the source and feeder relays across a 180–340 A fault-current window, confirming miscoordination. Adaptive relay settings and a detuned harmonic filter specification are proposed and validated, restoring coordination and reducing THD below statutory thresholds. The findings furnish Nigeria's first field-quantified evidence base for updating distribution codes, interconnection standards, and quality-of-supply regulation governing distributed PV on weak feeders, and a replicable measurement methodology for utilities across Sub-Saharan Africa.
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