The integration of distributed photovoltaic (PV) systems alters the traditional radial topology of distribution networks and increases the flexibility of electrical characteristics, causing the original protection devices to malfunction. Taking a typical 16‑node medium‑voltage distribution network as an example, this paper builds a simulation model in PSCAD and adopts the control‑variable method to investigate the effects of different PV capacities and different access locations on line protection. The results show that when a fault occurs near the bus‑side line end (e.g., the end of line 1‑2), as the PV capacity increases, the fault current flowing through the downstream protection (e.g., protection 2) rises significantly; when the capacity exceeds about 8.5 MW, it may exceed the setting value and cause maloperation. When a fault occurs near the load‑side line end (e.g., the end of line 3‑4), the currents of upstream protections (protections 1 and 2) decrease with increasing PV capacity, leading to possible refusal to trip. When the fault is close to the PV access point, a surge current occurs, severely disrupting the coordination between upstream and downstream protections. Moreover, the closer the PV access point is to the fault point, the larger the injected current; when the access point is at node 2, a surge of 31.8 kA appears, aggravating the risk of downstream protection maloperation. Based on these findings, two optimisation methods—directional overcurrent protection and pilot protection—are proposed for distribution networks with PV integration, aiming to mitigate the adverse effects and ensure stable operation.
 

distributed photovoltaic; distribution network; current protection; PSCAD; 16‑node system