Use of on-load tap changers in distribution transformers for enhanced renewable energy integration and acquisition : case study

Abstract

The increasing integration of rooftop solar PV systems into low-voltage (LV) distribution networks has introduced significant voltage regulation challenges. This study focuses on a real-world distribution transformer within the Sri Lankan electricity distribution network, where high solar penetration has led to persistent overvoltage issues across multiple feeders. Using OpenDSS modeling and field data, a range of mitigation strategies was analyzed, including power factor correction, parallel feeder installation, and fixed tap setting adjustments. Simulation results revealed that traditional approaches such as manual tap changes were either insufficient or impractical for sustained voltage control. While power factor correction helped reduce peak voltages, it also increased system losses and required deviations from grid standards. Parallel feeder installations, although technically viable, were cost-prohibitive and lacked demand justification. The study identifies the adoption of On-Load Tap Changers (OLTC) as the most effective solution. OLTCs offer real-time voltage regulation without the need for major infrastructure changes or policy modifications. The selected OLTC solution, which uses vacuum-based switching, was found to be cost-efficient, operationally reliable, and thermally robust, making it highly suitable for addressing the identified voltage issues. This thesis concludes that OLTC technology provides a scalable and sustainable pathway to enhance hosting capacity and ensure voltage stability in LV networks with high solar PV penetration