The rapid integration of large-scale solar photovoltaic (PV) plants into high-voltage transmission networks introduces new vulnerabilities to grid disturbances, particularly lightning strikes. This paper investigates the propagation of lightning-induced overvoltages from transmission lines to connected solar power plants, a critical issue given the geographical overlap of high solar irradiance and high lightning activity regions. The study employs Electromagnetic Transients Program (EMTP) simulations to model the system and evaluates the effectiveness of surge arresters as a primary protective measure.
The research is based on a simulation-driven methodology using the industry-standard EMTP-RV software for accurate modeling of electromagnetic transients.
The entire system—comprising the transmission line, solar plant collection grid, transformers, and surge protection devices—was modeled in EMTP. This allows for time-domain analysis of fast-front surges with nanosecond-to-microsecond resolution.
The lightning stroke is modeled using the Heidler current source function, a standard for representing the channel current: $i(t) = \frac{I_0}{\eta} \frac{(t/\tau_1)^n}{1+(t/\tau_1)^n} e^{-t/\tau_2}$. Parameters $I_0$ (peak current), $\tau_1$ (front time), and $\tau_2$ (tail time) were varied. The solar plant was modeled as an aggregate equivalent circuit, including DC cables, inverters, and step-up transformers.
Metal-Oxide Varistor (MOV) surge arresters were modeled at key locations: at the transmission line tower near the strike point and at the solar plant's main AC connection point. Their non-linear V-I characteristic is given by $i = k \cdot V^{\alpha}$, where $k$ and $\alpha$ are device constants.
Simulations covered a range of realistic lightning parameters:
Lightning strikes were simulated at varying distances (e.g., 0.5 km, 1 km, 2 km) from the solar plant's grid connection point along the transmission line. Both direct strikes to the phase conductor (shielding failure) and backflashovers due to tower strikes were considered.
The primary metric was the transient overvoltage magnitude at the solar plant's AC bus. Without surge arresters, overvoltages frequently exceeded 3.0 p.u. (per unit) of the system's nominal voltage for strikes within 1 km, posing a severe risk to inverter insulation. The overvoltage waveform is a superposition of the incoming surge and reflections within the plant's internal cabling network.
Beyond time-domain magnitude, the study performed spectral analysis.
The surge arresters demonstrated high effectiveness, typically limiting overvoltages to below 1.8 p.u., a level generally within the withstand capability of modern PV inverters (typically rated for 2.0-2.5 p.u. for short durations). The energy absorption requirement for the arresters was quantified, which is critical for proper sizing.
> 40%
Average reduction with arresters installed
< 1 km
Strikes within this range cause highest risk
The core of the EMTP model relies on solving the telegraph equations for the transmission line, coupled with non-linear component models:
Scenario: A 100 MW solar plant connected to a 230 kV transmission line via a 230/33 kV step-up transformer. A lightning stroke with Ip = 50 kA, tf = 2 µs hits a tower 0.8 km away, causing a backflashover.
Framework Application:
The findings have direct applications in the design and grid codes for large-scale solar facilities:
This paper correctly identifies a critical, yet often underestimated, fault line in the energy transition: the inherent conflict between optimal renewable siting and grid resilience. The authors pinpoint that the very regions boasting the highest solar yield (sunbelt areas) are frequently co-located with high isokeräunic levels (thunderstorm days per year). This isn't a minor coincidence; it's a fundamental siting dilemma. The research effectively shifts the narrative from viewing solar plants as passive, benign loads to recognizing them as active, vulnerable nodes that import and amplify grid-borne transients, threatening their own expensive power electronics—the inverters being the Achilles' heel.
The paper's logic is robust and follows a classic engineering risk-assessment pathway: Hazard Identification → System Modeling → Consequence Simulation → Mitigation Evaluation. It starts with the plausible hazard (lightning on the transmission corridor), models its propagation through the complex RLC network of lines and plant cabling (using the industry-validated EMTP tool), quantifies the damaging consequence (overvoltage exceeding inverter BIL), and finally tests a standard mitigation tool (surge arresters). The inclusion of both Fourier and Hilbert-Huang Transform analysis adds a valuable layer, moving beyond simple peak voltage to understand the frequency-domain signature of the threat, which is more relevant for semiconductor durability.
Strengths: The methodological rigor is commendable. Using EMTP, the gold standard for transient studies, lends immediate credibility. Parameter variation (current, distance) provides a useful sensitivity analysis. The focus on spectral analysis is a step above many purely time-domain studies.
Critical Flaws & Missed Opportunities:
For utilities, developers, and OEMs: